Impacts of Conservation Adoption on Cultivated Acres of Cropland in the Chesapeake Bay Region

Conservation Effects
Assessment Project
(CEAP)
Conservation Progress
Report

DECEMBER 2013

Impacts of Conservation
Adoption on Cultivated
Acres of Cropland in the
Chesapeake Bay Region,
2003-06 to 2011

This page intentionally left blank.

Cover Image: Land cover in the Chesapeake Bay region. Source: National Agricultural Statistics Service (NASS, 2007).
Suggested Citation: USDA NRCS. United States Department of Agriculture, Natural Resources Conservation Service. 2013. Impacts
of Conservation Adoption on Cultivated Acres of Cropland in the Chesapeake Bay Region, 2003-06 to 2011. 113p.

CEAP—strengthening the science base for natural resource conservation
The Conservation Effects Assessment Project (CEAP) was initiated by USDA’s Natural Resources Conservation Service (NRCS),
Agricultural Research Service (ARS), and National Institute of Food and Agriculture (NIFA) [formally known as Cooperative State
Research, Education, and Extension Services (CSREES)] in 2002 as a means by which to analyze societal and environmental benefits
gained from the 2002 Farm Bill’s substantial increase in conservation program funding. The original goals of CEAP were to estimate
conservation benefits for reporting at the national and regional levels and to establish the scientific understanding of the effects and
benefits of conservation practices at the watershed scale. As CEAP evolved, the scope was expanded to assess the impacts and
efficacy of various conservation practices on maintaining and improving soil and water quality at regional, national, and watershed
scales.
CEAP activities are organized into three interconnected efforts:
• Bibliographies, literature reviews, and scientific workshops to establish what is known about the environmental effects of
conservation practices at the field and watershed scale.
• National and regional assessments to estimate the environmental effects and benefits of conservation practices on the landscape
and to estimate conservation treatment needs. The four components of the national and regional assessment effort are Cropland;
Wetlands; Grazing lands, including rangeland, pastureland, and grazed forestland; and Wildlife.
• Watershed studies to provide in-depth quantification of water quality and soil quality impacts of conservation practices at the
local level and to provide insight on what practices are the most effective and where they are needed within a watershed to achieve
environmental goals.
CEAP benchmark results, currently published for six watersheds, provide a scientific basis for interpreting conservation practice
implementation impacts and identifying remaining conservation practice needs. These reports continue to inform decision makers,
policy makers, and the public on the environmental and societal benefits of conservation practice use.
Additional information on the scope of the project can be found at http://www.nrcs.usda.gov/technical/nri/ceap/.

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This report was prepared by the Conservation Effects Assessment Project (CEAP) Cropland Modeling Team and published by the
United States Department of Agriculture (USDA), Natural Resources Conservation Service (NRCS). The modeling team consists of
scientists and analysts from NRCS, the Agricultural Research Service (ARS), the University of Massachusetts, and Texas A&M
AgriLife Research.
Natural Resources Conservation Service, USDA
Lee Norfleet, Project Coordinator, Temple, TX, Soil Scientist
Jay Atwood, Temple, TX, Agricultural Economist
Tim Dybala, Temple, TX, Civil Engineer
Ann Graham, Temple, TX, Senior Editor
Maria Hrebik, Temple, TX, Civil Engineer
Kevin Ingram, Beltsville, MD, Agricultural Economist
Mari-Vaughn Johnson, Temple, TX, Agronomist
Chris Lester, Temple, TX, Soil Conservationist
Daryl Lund, Beltsville, MD, Soil Scientist
Loretta Metz, Temple, TX, Rangeland Management Specialist
Evelyn Steglich, Temple, TX, Natural Resource Specialist
Agricultural Research Service, USDA, Grassland, Soil, and Water Research Laboratory, Temple, TX
Jeff Arnold, Agricultural Engineer
Daren Harmel, Agricultural Engineer
Mike White, Agricultural Engineer
Blackland Research and Extension Center, Texas A&M AgriLife Research, Temple, TX
Tom Gerik, Director
Santhi Chinnasamy, Agricultural Engineer
Mauro Di Luzio, Research Scientist
Arnold King, Resource Conservationist
David Moffitt, Environmental Engineer
Theresa Pitts, Programmer
Xiuying (Susan) Wang, Agricultural Engineer
Jimmy Williams, Agricultural Engineer
University of Massachusetts Extension, Amherst, MA
Stephen Plotkin, Water Quality Specialist
The study was conducted under the direction of Micheal Golden, Deputy Chief for Soil Science and Resource Assessment, Michele
Laur, Director for Resource Assessment Division, and Douglas Lawrence, former Deputy Chief for Soil Survey and Resource
Assessment, NRCS. Executive support was provided by NRCS Chief Jason Weller, and former NRCS Chief Dave White.

Acknowledgements
The team thanks Shiela Corley, Torey Lawrence, Esmerelda Dickson, and Julia Klapproth, USDA National Agricultural Statistics
Service, for leading the survey data collection effort; Mark Siemers and Todd Campbell, CARD, Iowa State University, for
providing I-APEX support; NRCS field offices for assisting in collection of conservation practice data; Dean Oman, USDA NRCS,
Beltsville, MD, for geographic information systems (GIS) analysis support; Armen Kemanian, Penn State University, for improving
the denitrification routine in APEX; Peter Chen, Susan Wallace, George Wallace, and Karl Musser, Paradigm Systems, Beltsville,
MD, for graphics support, National Resources Inventory (NRI) database support, Website support, and calculation of standard errors;
and many others who provided advice, guidance, and suggestions throughout the project.
Last, but certainly not least, our gratitude is owed to the producers, land operators, farmers and ranchers, without whose continued
cooperation the CEAP effort, including this report, would not be possible.

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Foreword
This report marks the first revisit of a region originally surveyed and assessed by the USDA NRCS through the Conservation Effects
Assessment Project (CEAP) (USDA NRCS 2011). The original Chesapeake Bay report was the second report released in the national
CEAP series of regional reports, continuing the tradition within USDA of assessing the status, condition, and trend of natural
resources to determine how to improve conservation programs to best meet the Nation’s needs. The regional CEAP reports use a
sampling and modeling approach to quantify the environmental benefits that farmers and conservation programs currently provide to
society, and to explore prospects for attaining additional benefits with further or alternative conservation treatment.
The original report, based on a 2003-06 survey and published in 2011, provides quantified reference points against which to compare
subsequent studies, including this report. The revisit to the region allows examination of the changes and trends in conservation
practice use over time by comparing the baseline 2003-06 survey results with the results from the 2011 survey. The comparison
illuminates changes in patterns and impacts of voluntary conservation adoption in the Chesapeake Bay region. This resurvey improves
our scientific understanding of the effects and benefits of conservation practices at the watershed scale and increases the scientific
knowledge base helping policy makers implement appropriate programs and helping land managers and farmers apply appropriate
practices to best meet conservation goals in the region.
This report differs from the 2011 published “Assessment of the Effects of Conservation Practices on Cultivated Cropland in the
Chesapeake Bay Region” in several key aspects. The two reports cover the same areal extent, but the survey data for the original
report was collected over a multi-year period (2003-06) as part of the original CEAP national survey, while the resurvey activity
occurred only in the Chesapeake Bay region and solely in the fall of 2011. During the interim between the publication of the
benchmark report in 2011 and this report, there have been numerous improvements and updates performed on the Agricultural
Policy/Environmental eXtender (APEX) and Soil Water Assessment Tool (SWAT) models, improvements in soils input data,
increased weather data availability, and refinement of analytical techniques for evaluating the model results. As these changes
impacted data interpretation, model function, and results, the 2003-06 data was reanalyzed alongside the 2011 data. The more robust
approach utilized in this analysis produced results that differ from the results reported in the original USDA NRCS CEAP report for
the Chesapeake Bay region (USDA NRCS 2011). Therefore, readers of both reports will notice differences in certain results,
procedures, and interpretations.
The United States Department of Agriculture (USDA) has a rich tradition of working with farmers and ranchers to enhance
agricultural productivity and environmental conservation through voluntary programs. Many USDA programs provide financial
assistance to producers to encourage adoption of conservation practices appropriate to local soil and site conditions. Other USDA
programs, in tandem with state and local programs, provide technical assistance to design, install, and implement conservation
practices that are consistent with farmer objectives and policy goals. By participating in USDA conservation programs, producers are
able to:




install structural practices such as riparian buffers, grass filter strips, terraces, grassed waterways, and contour farming, all of
which reduce erosion, sedimentation, and nutrients leaving the field;
adopt conservation systems and practices such as conservation tillage, comprehensive nutrient management, integrated pest
management, and irrigation water management, which conserve resources and maintain the long-term productivity of crop and
pastureland; and
retire land too fragile for continued agricultural production by planting and maintaining on them grasses, trees, or wetland
vegetation.

As soil and water conservation remain a national priority, it is imperative to quantify the effectiveness of current conservation
practices and identify the potential for improving conservation gains. Over the past several decades, as the relationship between crop
production and the environment in which it occurs has become better understood, goals have shifted from solely preventing erosion to
achieving sustainable agricultural productivity by balancing the trade-offs associated with agricultural production and other potential
ecosystem services. Expansion of our scientific understanding of agroecological systems has contributed to a broadening of USDA
conservation policy objectives and development of more sophisticated conservation planning, practice design, and implementation.
These more holistic conservation goals and management approaches enable the Natural Resources Conservation Service (NRCS) to
work with farmers and ranchers to plan, select, and apply conservation practices that enable their operations to produce food, forage,
and fiber while conserving the Nation’s soil and water resources.

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Impacts of Conservation Adoption on Cultivated Acres of Cropland in
the Chesapeake Bay Region, 2003-06 to 2011
Contents

Page

Key Findings ...................................................................................................................................................................5
Executive Summary .......................................................................................................................................................6
Chapter 1: Sampling and Modeling Approach ...........................................................................................................13
Scope of Study ..........................................................................................................................................................13
Sampling and Modeling Approach ...........................................................................................................................13
Sampling: The NRI-CEAP Cropland Survey ...........................................................................................................14
Modeling Changes, Issues, and Assumptions ...........................................................................................................15
Simulating the Effects of Weather ............................................................................................................................16
Watersheds................................................................................................................................................................16
Chapter 2: Evaluation of Changes in Conservation Practice Use – 2003-06 to 2011 ...............................................18
Historical Context for Conservation Practice Use ....................................................................................................18
Structural Conservation Practices .............................................................................................................................19
Residue and Tillage Management Practices .............................................................................................................20
Conservation Crop Rotation .....................................................................................................................................23
Cover Crops and Winter Cover ................................................................................................................................24
Irrigation Management Practices ..............................................................................................................................26
Nutrient Management Criteria ..................................................................................................................................26
Survey Results: Nutrient Management Practices ......................................................................................................28
Nutrient Application Management Treatment Levels ...............................................................................................34
Manure Management ................................................................................................................................................35
Chapter 3: Onsite (Field-Level) Effects of Conservation Practices ...........................................................................38
The Field-Level Cropland Model—APEX ...............................................................................................................38
Effects of Practices on Fate and Transport of Water ................................................................................................39
Effects of Practices on Water Erosion and Sediment Loss .......................................................................................39
Effects of Practices on Soil Organic Carbon ............................................................................................................44
Effects of Practices on Nitrogen Loss .......................................................................................................................48
Effects of Practices on Phosphorus Loss ..................................................................................................................53
Chapter 4: Assessment of Conservation Treatment Needs ........................................................................................57
Conservation Treatment Levels ................................................................................................................................57
Inherent Vulnerability Factors ..................................................................................................................................66
Estimation of Remaining Conservation Treatment Needs ........................................................................................66
Changes in Conservation Treatments and Treatment Needs, by Resource Concern ................................................70
Chapter 5: Offsite Water Quality Effects of Conservation Practices ........................................................................73
The Soil and Water Assessment Tool—SWAT ........................................................................................................73
Source Loads and Instream Loads ............................................................................................................................76
Conservation Practice Effects on Water Quality ......................................................................................................78
Summary of Conservation Practice Effects on Water Quality in the Chesapeake Bay Watershed ..........................93
References .......................................................................................................................................................................97
Appendices ......................................................................................................................................................................99

Documentation Reports
There are a series of documentation reports and associated publications by the modeling team posted on the CEAP website at:
http://www.nrcs.usda.gov/technical/nri/ceap.

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Impacts of Conservation Adoption on Cultivated Acres of Cropland in
the Chesapeake Bay Region, 2003-06 to 2011
Key Findings
The voluntary, incentives-based conservation approach continues to be effective. Historic levels of conservation implementation are
achieving unprecedented results in the Chesapeake Bay region. Farmers, ranchers, and forestland owners voluntarily install or adopt
conservation practices on their lands as part of a conservation plan, in partnership with USDA’s Natural Resources Conservation
Service (NRCS), soil and water conservation districts, state agencies, and private organizations. These voluntary and collaborative
investments help support agricultural producers and rural economies, protect wildlife habitat, and improve water quality in the
Chesapeake Bay region.
The first national Conservation Effects Assessment Project (CEAP) farmer surveys documented the conservation and production
practices in place from 2003-06 and informed the original Chesapeake Bay region CEAP report, the “Assessment of the Effects of
Conservation Practices on Cultivated Cropland in the Chesapeake Bay Region” (USDA NRCS 2011). This report demonstrated that
during the time period 2003-06, most cropland acres in the Chesapeake Bay region were treated with structural or residue management
conservation practices, or both, with the goal of controlling erosion, reducing nutrient losses, and improving soil and water quality. In
order to provide more up-to-date information and assess the benefits of more recent conservation investments in the Chesapeake Bay
region, NRCS performed a second CEAP survey in the region during the fall of 2011 and covered the conservation and production
practices in use from 2009 to 2011.
This new report, “Impacts of Conservation Adoption on Cultivated Acres of Cropland in the Chesapeake Bay Region, 2003-06 to
2011,” using the data collected in 2003-06 and 2011, demonstrates that during the time between the two surveys, agricultural
producers have significantly increased their use of an array of conservation measures to improve and protect water and soil quality in
the Chesapeake Bay region. These conservation practices are generating substantial natural resource benefits for producers and the
communities of the Chesapeake Bay region.
These additional conservation measures have resulted in reductions in rill erosion rates by 57 percent and edge-of-field sediment
losses by 62 percent since 2006. In addition, the average annual rate of soil carbon loss was reduced by 50 percent. The 2011 survey
results indicate that edge-of-field nitrogen losses in surface runoff were reduced by 38 percent, nitrogen losses in subsurface flows
were reduced by 12 percent, and phosphorus losses were reduced by 45 percent compared to 2003-06 loss rates. The edge-of-field
conservation achievements on the Chesapeake Bay watershed’s cropped acres ultimately helped the Chesapeake Bay itself by
reducing the total cumulative instream delivery from all sources (urban, rural, point, and non-point). In fact, achievements in
agricultural conservation adopted between 2003-06 and 2011 reduced the cumulative instream loads delivered to the Chesapeake Bay
by 8 percent for sediment, 6 percent for nitrogen, and 5 percent for phosphorus. These percentage reductions equate to annual
reductions of 15.1 million tons of sediment and 48.6 million pounds and 7.1 million pounds of nitrogen and phosphorous, respectively.
Structural practices, including buffers or terraces, play important controlling and trapping functions in the “Avoid, Control, Trap”
(ACT) conservation system approach for reducing losses of sediment and nutrients from cropland acres. Structural practices were in
use on 52 percent of cropped acres in 2003-06. By 2011, structural practices were adopted on 66 percent of cropped acres, or a 27
percent increase between the survey periods.
Annual practices such as cover crops and conservation tillage serve all three important avoiding, controlling, and trapping functions in
the ACT conservation system approach. Conservation tillage adoption on one or more crops in rotation increased from occurring on
74 percent of cropped acres in 2003-06 to 90 percent of cropped acres in 2011. As for cover crop use, farmers substantially expanded
their use of this core ACT practice. In the 2003-06 survey, only 5 percent of cropped acres in the Chesapeake Bay region used cover
crops every year and 88 percent of cropped acres were never planted to cover crops; in the 2011 survey, however, the number of
cropped acres that farmers planted to cover crops every year more than tripled (to 18 percent of cropped acres) and more than half of
all cultivated acres in the region (52 percent) had cover crops applied at least one out of every four years.
Livestock and poultry producers have improved their manure management practices in recent years, leading to manure being spread
on more acres in the region in 2011 than it was in 2003-06. The number of acres receiving manure increased almost 30 percent
(growing from 37 percent to 48 percent of cropped acres receiving manure between the 2003-06 and 2011 surveys). Likewise, as an
indicator of enhanced nutrient management, there was nearly a 147 percent increase in soil testing on manured acres prior to applying
more manure (increasing from 15 percent to 37 percent of cropped acres between the surveys). There are also indications of a growing
manure market in the region. Manured acres applied with purchased, rather than manure produced-on-farm, nearly quadrupled,
increased from 57,000 acres in 2003-06 to 203,000 acres in 2011.

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Progress has been made toward addressing conservation needs, and opportunities exist to increase conservation on cropped acres
in the Chesapeake Bay region. The conservation efforts of the region’s farmers on their own and with support from local, state, and
Federal programs, especially focused programs like the Chesapeake Bay Watershed Initiative (CBWI), have generated significant
progress in addressing conservation concerns on cropland acres with a high potential benefit for protecting and improving water
quality. Acres with high potential benefits are those that could respond well to additional conservation treatments and have the greatest
potential for losses of sediment and nutrients. Conservation measures adopted between 2003-06 and 2011 reduced the number of
cropped acres with high potential benefits by 80 percent, dropping from the 2003-06 level of 813,000 acres (19 percent of all cropped
acres) to 157,000 acres (4 percent of all cropped acres) in 2011. As of 2011, more than half the acres in the region were classified as
having low needs for additional conservation treatment. Compared to 2003-06 conditions, the additional conservation practices in
place in 2011 increased the number of acres with low conservation needs by almost 32 percent (or increasing from 41 percent of
cropped acres in 2003-06 to 54 percent in 2011).
Although significant gains were made in the controlling and trapping components of the ACT conservation system approach,
opportunities remain for progress in avoiding nutrient losses through improved nutrient application management. Specifically,
avoidance could be better achieved through better incorporation of the 4Rs (the right rate, the right timing, the right method, and the
right form) into nutrient management plans. Improvement in 4Rs implementation would be particularly beneficial on acres on which
manure application occurs because manure requires different application strategies than do commercial fertilizers.
Comprehensive conservation planning that incorporates targeting is essential for effectiveness and efficiency. Prioritizing one or
more conservation goals, identifying acres with the highest potential for conservation gains per conservation dollar investment, and
identifying the appropriate suites of treatments for each acre significantly improves the effectiveness of conservation practice
implementation and increases the value of the conservation dollar. Suites of practices that comprehensively address all three
components of the ACT strategy are required to adequately address soil erosion, nutrient losses in runoff, and nitrogen losses through
leaching. This study shows that the increased use of additional conservation practices on acres with high potential benefits
significantly reduced losses due to runoff. The increased use of cover crops and winter annuals decreased leaching losses. Additional
gains will depend on continued use of current practices and continuing improvement in the application rate, timing, method, and form
of nutrients.

Executive Summary
Background on This Report
Historic levels of conservation implementation are achieving unprecedented results in the Chesapeake Bay region. Farmers, ranchers,
and forestland owners voluntarily install or adopt conservation practices on their lands as part of comprehensive conservation
planning, in partnership with USDA’s Natural Resources Conservation Service (NRCS), soil and water conservation districts, state
agencies, and private organizations. These voluntary and collaborative investments help support agricultural producers and rural
economies, protect wildlife habitat, and improve water quality in the Chesapeake Bay region.
The Conservation Effects Assessment Project (CEAP) is a multi-agency USDA effort to quantify the environmental effects of the
conservation practices adopted by producers. CEAP cropland reports integrate farmer surveys (conducted by NASS), natural resource
information (land use and soils), and modeling to estimate the impact of conservation practices on nutrient and sediment loadings. The
lead CEAP partners are USDA’s Natural Resources Conservation Service (NRCS) and Agricultural Research Service (ARS) and
Texas A&M AgriLife Extension Services.
NRCS released the first Chesapeake Bay region CEAP cropland assessment in March 2011, which relied on data gathered through
farmer surveys conducted from 2003 to 2006. The first report demonstrated that conservation practices and systems were delivering
benefits for the Bay watershed. The surveys informing for the first CEAP report were conducted too early to capture the growth in use
of cover crops in the Bay watershed, and also did not capture the impact of accelerated conservation implementation made possible
through the increased funding provided by State and Local partners, and by the Chesapeake Bay Watershed Initiative (CBWI),
authorized in the 2008 Farm Bill.
There was considerable interest among Chesapeake Bay stakeholders in updating the 2011 report with new farmer surveys to evaluate
the progress made by Bay farmers since 2006. NRCS conducted a new set of farmer surveys in late 2011, and also updated the CEAP
models and improved soils and weather data. This is the first time NRCS has updated a CEAP cropland report for a particular region,
allowing for comparison in conservation effects between two points in time. The results indicate that conservation planning and
practice implementation being adopted by Chesapeake Bay farmers are producing substantial water quality benefits by reducing
sediment and nutrient delivery to the Chesapeake Bay. Because NRCS conservation efforts complement those of private landowners,
non-governmental organizations, other Federal, State, and local agencies working toward natural resources conservation and reduction
of nutrient and sediment losses into the Chesapeake Bay, this report considers impacts of all conservation practices, regardless of
NRCS involvement.

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Cultivated Cropland Acres in the Chesapeake Bay Region Receiving Conservation Treatment Under USDA Programs. Data
are broken out by program or initiative. Totals are not summed by year because the same acreage may be counted under multiple
programs or initiatives and acres treated over multiple years were counted in each year of treatment. Treatment costs vary by acre and
treatment applied.
Acres Receiving Federal Assistance
Chesapeake Bay Watershed Initiative
Conservation Reserve Program
Financial Assistance Programs
Conservation Technical Assistance

2003-06
36,337
131,122
250,760

2007
20,083
130,504
278,538

2008
11,481
125,995
302,096

2009
4,349
5,939
133,748
294,370

2010
89,321
5,050
95,486
305,454

2011
111,350
4,057
66,648
292,813

This report demonstrates substantial conservation practice adoption and improvement of conservation benefits between the 2003-06
and 2011 sampling periods. However, this report does not capture the full impact of the conservation partnership’s focused
conservation efforts in the Chesapeake Bay region since 2008, or the full impacts of the 2008 Farm Bill’s financial contributions to the
region. Since 2011, when the farmer survey informing this report was conducted, various Federal, State, and local agencies and
entities in the District of Columbia and the six states in the Chesapeake Bay region have continued to work with farmers to accelerate
conservation practice adoption. State and Federal programs have expanded incentives for cover crop adoption, manure incorporation,
use of variable rate applications, side-dressing of nutrients, and other production techniques targeted at reducing losses of sediment
and nutrients from farm fields. Based on the analyses in this report, we anticipate that the focused funding efforts will continue to
accelerate conservation gains in the region.

Overview of Data Collection and Modeling
In March 2011, the NRCS released the “Assessment of the Effects of Conservation Practices on Cultivated Cropland in the
Chesapeake Bay Region”, the benchmark USDA NRCS CEAP report on the Chesapeake Bay region (USDA NRCS 2011). This report
relied on data collected between 2003-06 and provides an historical point of reference by which to measure progress in conservation
adoption and conservation practice efficacy in the region. Due to stakeholder interest and an increased focus on farmer conservation
adoption since the last survey was completed in 2006, NRCS prioritized a second assessment of the state of conservation practice
adoption and achievements on cropped acres in the Chesapeake Bay region. Farmer surveys for this assessment were conducted in the
fall of 2011.
The benchmark survey (2003-06), in combination with the resurvey in 2011, enables this report’s statistically based identification and
quantification of emergent trends in agricultural conservation impacts in the Chesapeake Bay region between 2003-06 and 2011. This
is the first CEAP report in which a watershed is revisited for a second round of analyses. This study reports on changes in
conservation adoption, estimates the impact of these changes on reduction of both edge-of-field losses and instream sediment and
nutrient loads delivered to the Chesapeake Bay, and evaluates the need for additional conservation treatment on cropland in the region.
The analyses reflect the environmental impact of management of the region’s cropped acres, which makes up 10 percent of the
Chesapeake Bay region (4.35 million acres). Changes in and impacts of agricultural conservation practices were isolated from other
land use changes and impacts by holding other land uses (hay, pasture, urban point and non-point, forests, etc.) and their management
constant at 2003-06 conservation levels for analyses of both the 2003-06 and 2011 data. Therefore, all changes in nutrient and
sediment dynamics observed in the simulations comparing the 2003-06 baseline condition with the 2011 conservation condition are
solely attributable to changes in agricultural practices. It is not the intent of this report to estimate progress toward the overall regional
goals related to conservation practice changes on land uses other than cultivated cropland.
Simulation models were used to estimate the effects of conservation practices. During the interim between the publication of the
original report in 2011 and this report, there have been numerous improvements and updates performed on the Agricultural
Policy/Environmental eXtender (APEX) and Soil Water Assessment Tool (SWAT) simulation models, improvements in soils input
data, increased weather data availability, and refinement of analytical techniques for evaluating the model results. The 2003-06 data
was reanalyzed using the same model version and data interpretation used to analyze the 2011 data in order to allow the 2003-06 data
to inform a baseline condition by which to assess changes between the two survey periods. The more robust approach used in this
analysis produced results that differ from the results reported in the original USDA NRCS CEAP report for the Chesapeake Bay
region (USDA NRCS 2011). Therefore, readers of both reports will notice differences in certain results, procedures, and
interpretations.
The National Resources Inventory (NRI), a statistical survey of conditions and trends in soil, water, and related resources on U.S. nonFederal land conducted by USDA NRCS, provides the statistical framework for the analyses. The same framework was used for both
sets of data collections, although the data collection informing the 2003-06 conservation practice use assessment was part of a national
survey and the data collection informing 2011 practice trends was collected in a regional survey. This statistical framework allows for
comparison between the original survey and all resurveys, all of which represent the region and are not subject to bias due to land-use
conversion at any sample point (i.e., conversion of cropland to urban land).

7

Information on farming activities and conservation practices was obtained primarily from a farmer survey designed for CEAP by the
USDA National Agricultural Statistics Service (NASS). Additional practice information was obtained from USDA Farm Services
Agency, the USDA NRCS NRI, and USDA NRCS field office records. This assessment is not directly reflective of Federal
conservation program benefits, as it includes impacts of the conservation efforts of local, State, and regional governmental agencies
and independent organizations, as well as those of individual landowners and farm operators.

Farmer Survey Summary
A 2011 farmer survey obtained information on the extent of conservation practice used in the Chesapeake Bay region for the period
2009 to 2011. The most extensive change observed since the 2003-06 survey was the increased adoption of structural practices,
conservation tillage, and cover crops. Nutrient management changes are best characterized as largely being maintained at 2003-06
conservation levels, with progress in some aspects countered by declines in others. While most acres have evidence of some nitrogen
or phosphorus management, there is opportunity to enhance existing nutrient management practices on most acres, especially on those
receiving manure. Consistent application of the 4Rs (right rate, right timing, right method, and right form) of nutrient application
management across all crops in a rotation is still a priority need. Skilled management is required to shift conservation planning to
match current production goals with soil types and effective nutrient application strategies. Maintaining production goals while
adopting new nutrient management strategies increases management complexity and risk to the farmer. The 2003-06 survey data
provides the baseline against which conservation gains could be measured; the following is an overview of key trends:
Changes in adoption of conservation tillage, structural practices, residue management, and cover crops on cultivated cropland
in the Chesapeake Bay region, 2003-06 to 2011:
 Structural practices for controlling water erosion: 14 percentage point increase, from 52 to 66 percent of cropped acres;
 Practices designed to trap sediment and nutrients at the edge-of-field: 17 percentage point increase, from 14 percent to 31
percent of cropped acres;
 Some form of conservation tillage without any conventional tillage: 23 percentage point increase, from 56 to 79 percent of
cropped acres;
 Continuous No-till on all crops in a rotation: 16 percentage point increase, from 38 to 54 percent of cropped acres; and
 Cover crops use at some point in rotation: 40 percentage point increase, from 12 to 52 percent of cropped acres.
Changes in nitrogen management, including commercial fertilizer and manure applications on cultivated cropland in the
Chesapeake Bay region, 2003-06 to 2011:
 Annual nitrogen application: 10 percent increase, from 95.0 to 104.5 pounds per acre per year, including a 9 percent increase
in commercial fertilizer application (6.7 pound per acre per year increase) and a 13 percent increase in manure nitrogen
application (2.8 pound per acre per year increase).
On cropped acres receiving commercial nitrogen and/or manure based nitrogen in 2003-06 and 2011:


Appropriate nitrogen application rate on all crops in rotation, including manure applications: 9 percentage point decline,
from 32 to 23 percent of cropped acres; appropriate nitrogen application timing on all crops in rotation, including manure
applications: 14 percentage point decline, from 50 to 36 percent of cropped acres; and appropriate nitrogen application
method on all crops in rotation, including manure applications: 7 percentage point decline, from 34 to 27 percent of cropped
acres.



Appropriate nitrogen application rate on none of the crops in rotation, including manure applications: 7 percentage point
decline, from 13 to 6 percent of cropped acres; appropriate timing on none of the crops in rotation, including manure
applications: maintained 2003-06 conservation level, 11 percent of cropped acres for both 2003-06 and 2011; and appropriate
nitrogen application method on none of the crops in rotation, including manure applications: maintained 2003-06
conservation level, 21 and 18 percent of cropped acres in 2003-06 and 2011, respectively.



Appropriate rate, timing, and method of nitrogen application, including manure applications:
 on some, but not all crops in rotation: 6 percentage point increase, from 87 to 93 percent of cropped acres;
 on all crops in the rotation: 6 percentage point decline, from 13 to 7 percent of cropped acres.

Changes in phosphorus management, including commercial fertilizer and manure applications on cultivated cropland in the
Chesapeake Bay region, 2003-06 to 2011:
 Annual phosphorus application: 6 percent increase, from 23.8 to 25.2 pounds per acre per year, including a 5 percent increase
in commercial fertilizer application (1.0 pound per acre per year increase) and an 11 percent increase in manure nitrogen
application (0.4 pound per acre per year increase).

8

On cropped acres receiving commercial phosphorus and or manure based nitrogen between 2003-06 and 2011:
 Appropriate phosphorus application rate on all crops in rotation, including manure applications: maintained 2003-06
conservation level, 54 and 57 percent of cropped acres in 2003-06 and 2011, respectively; appropriate phosphorus application
timing on all crops in rotation, including manure applications: 11 percentage point decline, from 53 to 42 percent of cropped
acres; and appropriate phosphorus application method on all crops in rotation, including manure applications: maintained
2003-06 conservation level, 42 and 37 percent of cropped acres in 2003-06 and 2011, respectively;


Appropriate phosphorus application timing on none of the crops in rotation, including manure applications: 6 percentage
point increase, from 13 to 19 percent of cropped acres; appropriate phosphorus application method on none of the crops in
rotation, including manure applications: maintained 2003-06 conservation level, 30 and 32 percent of cropped acres in 200306 and 2011, respectively; and



Appropriate rate, timing, and method of phosphorus application, including manure applications:
 on some, but not all crops in rotation: maintained 2003-06 conservation levels, 78 and 79 percent of cropped acres in
2003-06 and 2011, respectively; and
 on all applications in the crop rotation: maintained 2003-06 conservation levels, 22 and 21 percent of cropped acres in
2003-06 and 2011, respectively.

Changes in manure management (with or without supplemental commercial nutrient inputs) on cultivated cropland in the
Chesapeake Bay region, 2003-06 and 2011:
 Manure application rate: 25 percent increase, from 12.6 to 16.8 tons per acre per year;
 Manure application at some point in the crop rotation: 10 percentage point increase, from 38 to 48 percent of cropped acres;
 Manured acres applied with off-farm-sourced manure: 17 percentage point increase, from 17 to 34 percent of manured
cropped acres;
 Manured acres applied with purchased manure: 6 percentage point increase, from 4 to 10 percent of manured cropped acres;
and
 Management of manure as a nitrogen source on manured acres:
 Appropriate application rates for all crops in rotation: 8 percentage point decline, from 17 to 9 percent of manured
cropped acres; appropriate application timing for all crops in rotation: 6 percentage point decline, from 18 to 12 percent
of manured cropped acres; and appropriate application method on all crops: 6 percentage point decline, from 22 to 16
percent of manured cropped acres;
 Appropriate application rates for none of the crops in rotation: 15 percentage point decline, from 24 to 9 percent of
manured cropped acres; appropriate application timing for none of the crops in rotation: 6 percentage point decline,
from 16 to 10 percent of manured cropped acres; and appropriate application method for none of the crops in rotation:
maintained 2003-06 conservation levels, 16 and 17 percent of manured cropped acres in 2003-06 and 2011, respectively;
 Management of manure as a phosphorus source on manured acres:
 Appropriate application timing for none of the crops in rotation: 12 percentage point increase, from 16 to 28 percent of
manured cropped acres; appropriate application method for none of the crops in rotation: 14 percentage point increase,
from 30 and 44 percent of manured cropped acres; and
 Appropriate application timing for all crops in rotation: maintained 2003-06 conservation level, 16 and 13 percent of
manured cropped acres in 2003-06 and 2011, respectively; appropriate application method on all crops in rotation: 7
percentage point decline, from 28 to 21 percent of manured cropped acres.

Conservation Accomplishments
Compared to edge-of-field conservation accomplishments in the 2003-06 baseline condition, model scenarios suggest that practices
adopted in the 2011 conservation condition have further reduced agricultural impacts in the Chesapeake Bay region. Specifically,
compared to the 2003-06 baseline condition, the 2011 conservation condition has reduced:
 sediment loss from fields: 63 percent reduction, from 5.1 to 1.9 tons per acre per year;
 acres with sheet and rill erosion greater than soil loss tolerance (T): 17 percentage point reduction, from 28 to 11 percent of
acres;
 nitrogen loss with surface runoff, including nitrogen attached to sediment and nitrogen in solution: 38 percent reduction, from
15.7 to 9.7 pounds per acre per year;
 nitrogen loss in subsurface flows by leaching: 12 percent reduction, from 25.9 to 22.9 pounds per acre per year;
 total phosphorus loss from fields: 44 percent reduction, from 3.4 to 1.9 pounds per acre per year;
 acres losing soil organic carbon: 20 percentage point reduction, from 66 to 46 percent of cropped acres; and
 soil carbon loss from fields: 50 percent reduction, from 189 to 95 pounds per acre per year.
The comprehensive Avoid, Control, Trap (ACT) conservation system approach requires that all three aspects of the system be
accommodated with appropriate and complementary conservation practice adoption. Nutrient applications and tillage management are
necessary for crop production and even when appropriately applied will have losses of sediment and nutrients. Therefore losses that
9

cannot be avoided with these management approaches should be controlled within the field with practices such as terraces, grassed
waterways, or contouring. Some practices may serve the ACT strategy in multiple ways. For example, conservation tillage can both
serve to avoid losses and control losses. Practices designed to trap sediment and nutrients at the edge-of-field (e.g., filter strips and
buffers) are necessary for a complete approach to reducing the impacts of cultivated cropland on water quality. In the Chesapeake Bay
region, achievements in nutrient management have largely come from the control and trap components of the ACT system. Future
conservation practice success requires a renewed emphasis on the avoidance aspect of the system. Specifically, significant
improvements can be realized with more focus on implementing the 4Rs of nutrient application. Key among these is timing, with a
need to shift more nutrient applications to the time after crop has been planted, which matches nutrient application and availability
temporally with nutrient demand.
The simulated change in nitrogen dynamics between the 2003-06 baseline condition and the 2011 conservation condition demonstrate
the potential pitfalls of focusing on only one or two parts of the ACT strategy. Water erosion control practices were very effective at
controlling and trapping sediment and nutrients on farm fields. The widespread adoption of structural erosion control practices,
residue management practices, and reduced tillage slowed the flow of surface water runoff, allowing more sediment and nutrients to
remain into the field, as well as allowing more water to infiltrate into the soil. This re-routing of surface water to subsurface flows
redirects the soluble nitrogen into subsurface flows and may potentially extract additional nitrogen from the soil as the water filters
through the soil profile. Although the 2011 conservation condition reduced nitrogen losses via subsurface flow by 12 percent on
cropped acres as compared to the 2003-06 baseline condition, high losses of nitrogen in subsurface flows remain a challenge in the
region.

Gains Related to Cover Crop and Winter Cover Use
In the context of this report, cover crops are considered a unique subset of winter cover. Cover crops are planted for agroecological
purposes, including soil and nutrient conservation and soil health benefits. Cover crops are grown when principal crops are not
growing (this typically includes, but is not limited to, winter months). Cover crops are not planted with the intent to harvest and are
generally terminated by tillage or herbicide application prior to maturity. Winter cover includes crops (mostly small grains planted for
spring harvest) that may be grazed and or harvested for grain, hay, or both.
In 2003-06, only 5 percent of cropped acres in the Chesapeake Bay region had cover crops planted every year and 88 percent of acres
never had any cover crops planted. In 2011, 52 percent of acres had cover crops planted at least once every 4 years and 18 percent of
acres had cover crops planted every year. It was estimated that relative to the 2003-06 baseline condition, the increased annual use of
cover crops in the 2011 conservation condition enhanced reduction in sediment loss by an average of 78 percent, surface loss of
nitrogen by 35 percent, subsurface nitrogen loss by 40 percent, and total phosphorus loss by 30 percent. In the 2011 conservation
condition, the average annual rate of carbon change due to annual application of cover crops improved by an average 148 percent as
compared to carbon dynamics in the 2003-06 baseline condition. State incentive programs have been pivotal in the continued
increases in cover crop adoption. For example, in 2011 Maryland farmers, supported through the state’s Cover Crop Program,
voluntarily planted nearly 430,000 acres to cover crops.
Winter cover adoption, other than cover crops, increased as well. In 2003-06 only 3 percent of cropped acres in the region were
planted with winter cover annually, but by 2011 annual winter cover was grown on 17 percent of cropped acres. In 2003-06 winter
cover was a part of crop rotations at least 1 out of every 4 years on only 47 percent of acres and by 2011, 65 percent of cropped acres
in the region had the soil covered during at least one winter in a 4-year crop rotation. The increased use of winter annuals in the crop
rotation may be attributed to market forces and the flexibility in cover crop programs, such as those which allow farmers to opt to
manage their intended cover crop for grain harvest in return for a reduced or no cost share on the cover crop.
For 2011, a comparison between acres with no winter cover and those adopting some form of cover during the winter months for at
least part of the crop rotation, show that winter cover adoption, solely or along with other conservation activities as shown in table 2.4:
 reduced sediment losses by 37 percent;
 reduced surface losses of nitrogen by 28 percent;
 reduced subsurface losses of nitrogen by 18 percent;
 reduced total phosphorus losses by 29 percent; and
 reduced carbon losses by 46 percent.

Reductions in Conservation Treatment Needs
The conservation practices reported in the 2011 survey of the Chesapeake Bay region were compared to the conservation practice
conditions reported in the 2003-06 survey to evaluate remaining conservation treatment needs. Acres with high potential benefits to
water quality (“high conservation needs acres”) are the most vulnerable of the acres, have the least conservation treatment, and have
the highest losses of sediment and/or nutrients. Acres with moderate potential benefits to water quality (“moderate conservation
needs acres”) generally have lower levels of inherent vulnerability or have more existing conservation practices in use than do high

10

conservation needs acres. For the purposes of this report, acres with currently low potential benefits to water quality (“low
conservation needs acres”) are considered to be sufficiently treated; combinations of conservation practices on these acres address all
the inherent vulnerability factors that determine the potential for sediment and nutrient losses.
Simulations and analyses show conservation treatment needs for the Chesapeake Bay region were reduced between the 2003-06
baseline condition and the 2011 conservation condition, but opportunities for improvement remain on nearly half of the acres in the
region:
 Cropped acres with high needs for additional conservation treatment for one or more resource concern: 15 percentage point
decline, from 19 to 4 percent of cropped acres;
 Cropped acres with moderate needs for additional conservation treatment for one or more resource concern: maintained 200306 conservation levels, at 40 and 42 percent of cropped acres in 2003-06 and 2011, respectively; and
 Cropped acres with adequate conservation treatment, or low needs for additional conservation treatment for one or more
resources concern: 13 percentage point increase, from 41 to 54 percent of acres. 1
Significant progress was made on adoption of complementary structural and vegetative practices, such as cover crops, edge-of-field
filters, and buffers, all of which reduce sediment and nutrient losses associated with runoff. Under the 2011 conservation condition,
only 15 percent of cropped acres were in need of additional treatments to prevent sediment loss and only 11 percent of acres required
treatment for sheet and rill erosion to prevent exceedance of the soil loss tolerance (T). In the 2003-06 baseline condition, 42 percent
of acres had additional need for erosion control treatment and 28 percent were in need of further treatment to prevent exceedance of T.
In the 2011 conservation condition, only 3 percent of cropped acres had a high need for additional soil erosion control and 12 percent
had a moderate need. Adoption of the complementary structural and vegetation practices also contributed to a shift in carbon trends on
cropped acres in the Chesapeake Bay region, which were, on average, losing carbon in the 2003-06 baseline condition, but were, on
average, maintaining carbon in the 2011 conservation condition. Conservation gains made largely via adoption of practices such as
cover crops, conservation tillage, and high residue crop rotations require careful planning and persistence in order to maintain the
levels of erosion reduction, sediment loss reduction, and carbon gain realized in 2011 conservation condition.
The greatest conservation need in the region in 2003-06 remained the greatest opportunity for increased conservation gains in 2011:
adoption of consistent nutrient application management adhering to the 4Rs: right rate, timing, method, and form of application. In
some cases, only minor adjustments to an existing nutrient management plan are needed to bring the management up to current
standards (590 practice code for Nutrient Management), while other acres require more extensive adjustments.
As of 2011, most cropped acres had some nutrient application management practices in use, but 46 percent of cropped acres in the
region would benefit from additional treatment to better prevent sediment, nitrogen, or phosphorus loss from fields. Although all acres
with high needs for subsurface flow losses were treated in the 2011 conservation condition, 36 percent of cropped acres still needed
conservation treatments to address nitrogen loss in subsurface flow pathways, most of which returns to surface water through drainage
ditches, tile drains, natural seeps, and groundwater return flow. Adoption of erosion control prevention practices reduced acreage
needing treatment for surface nitrogen losses from 35 to 14 percent of cropped acres between the 2003-06 baseline condition and 2011
conservation condition, respectively.

Effects of Conservation Treatment on Water Quality in the Chesapeake Bay
Reductions in edge-of-field losses translate into potential improvements in water quality in streams and rivers in the region. Transport
of sediment and nutrients from farm fields to streams and rivers and ultimately into the Bay involves a variety of processes and timelags. Nutrient and sediment dynamics at the edge-of-field do not directly or immediately relate to instream loads measured in rivers,
streams, and the Bay, all of which may be impacted by storm events, tidal surges, and the legacy of past land use and management.
2011 Agricultural Achievements in Conservation
Relative to conditions simulated in the “no-practice scenario”, in which no conservation practices were applied to cultivated cropland,
the 2011 conservation condition reduced total loads delivered from the edge-of-field to rivers and streams by:
 82 percent for sediment;
 44 percent for nitrogen; and
 75 percent for phosphorus.
As compared to the 2003-06 baseline condition, the 2011 conservation condition reduced delivery by:
 60 percent for sediment;
 20 percent for nitrogen; and
 41 percent for phosphorus.

1

Rounding causes apparent mathematical discrepancies.

11

Sediment and nutrients being delivered to the Chesapeake Bay come from a variety of sources, including cultivated cropland, hayland,
forestland, and urban lands. This is not an assessment of overall progress in conservation on all acreage in the Chesapeake Bay.
Rather, this report holds the sediment and nutrient contributions of all other land uses at their 2003-06 levels for all analyses, enabling
an unencumbered comparison of gains made due to changes on cultivated cropland between the 2003-06 and 2011 surveys. Relative to
the no-practice scenario, the 2011 conservation condition reduced total loads delivered to the Bay (all sources – instream loads) by:
 22 percent for sediment;
 17 percent for nitrogen; and
 21 percent for phosphorus.
As compared to the 2003-06 baseline condition, the 2011 conservation condition reduced delivery by:
 8 percent for sediment;
 6 percent for nitrogen; and
 5 percent for phosphorus.
Targeting
Not all acres suffer the same losses and not all acres provide the same benefit from conservation treatment. Some acres are inherently
more vulnerable, such as those that are highly erodible or have leaching-prone soils. These more vulnerable acres tend to lose more
sediment and/or nutrients than do less vulnerable acres. Therefore greater per-acre benefits can be attained with focused
comprehensive conservation treatment on these most vulnerable acres. One strategy of conservation treatment is to target the soils
with the highest inherent erosion and leaching risks for enhanced treatment with a comprehensive conservation treatment plan. In the
case of the Chesapeake Bay, the region as a whole has been targeted with an intensification of conservation practices and conservation
programming, including the Chesapeake Bay Watershed Initiative. Analyses included in this report demonstrate that this regional
targeting approach is working. However, while substantial progress has been achieved, there are still undertreated acres on which
improved conservation practice adoption could make significant impacts on sediment and nutrient losses.

12

Chapter 1
Sampling and Modeling Approach
Scope of Study
This study was designed to provide a regional-scale evaluation
of the trends in and effects of conservation practice adoption
in the Chesapeake Bay region in 2003-06 as compared to
2011. This report considers conservation practice impacts at
two scales: at the edge-of-field and on instream water quality.
Simulated sediment, soil carbon, nitrogen, and phosphorus
dynamics related to reported changes in conservation practice
adoption are analyzed. This report:
 Evaluates the extent of conservation practice adoption
in the region as of 2011, with specific comparison to
the benchmark condition observed in 2003-06 and a
hypothetical “no-practice” condition in which no
conservation practices are applied;
 Estimates the anticipated long-term environmental
benefits and effects of conservation practices in use in
2011, with specific comparison to anticipated longterm effects of practices in place in 2003-06 and a
hypothetical “no-practice” condition in which no
conservation practices are applied; and
 Estimates conservation treatment needs on cropped
acres in the region as of 2011, with specific
comparison to conservation treatment needs on
cropped acres identified during the benchmark period
of 2003-06.
This study quantifies and compares the anticipated long-term
impacts of conservation practices in place in 2003-06 and
2011, regardless of how, when, or why the practices came to
be in use. It includes practices adopted by farmers on their
own, as well as practices that are the result of state or local
programs. Because it is not restricted to practices associated
with Federal conservation programs, this report should not be
considered an evaluation of Federal conservation programs.
The model results provide estimates of average benefits
achievable through long-term adoption of the conservation
practices surveyed to be on the ground in 2003-06 or 2011.
These long-term estimates are based on the assumption that
weather patterns observed over the last half century continue
into the future. The long-term nature of the simulations also
produces results that may be expected once conservation
practices on the ground in 2003-06 and 2011 actually take
effect. This report was designed to provide a long-term view
of conservation practice impacts, rather than to simulate water,
sediment, and nutrient dynamics actually observed in the years
2003-06 and 2011. Due to the impacts of legacy sediments and
legacy nutrients, the benefits of conservation practices are
often not measureable for a number of years post-installation.
To put this another way, the instream measurements taken in
2003-06 and 2011 reflect the legacy of prior management
rather than the benefits of conservation practices on the
ground during the two survey periods. Legacy impacts and
associated time-lags are further addressed in Chapter 5, which
also addresses benefits of agricultural conservation practices
on sediment and nutrient loads delivered to the Chesapeake
Bay.

It is beyond the scope of this report to estimate gains that
could be attained with adoption of additional conservation
treatments beyond those in use in 2011. A subsequent
publication will explore the potential impacts of enhanced
conservation practice adoption and targeting of specific
acreage for various natural resource goals. The subsequent
publication will also consider more specific economic aspects
of natural resource management in the Chesapeake Bay
region, including estimation of benefits associated with
various investment strategies and increments of investment in
conservation on cropped acres in the region.
National Resources Inventory (NRI) data were updated
between the two survey periods, enabling the update of
cropped acres for the 2011 period. The 2003-06 cropped acre
estimates are based on acreage weights derived from the 2003
NRI, while the estimates for cropped acres in 2011 are based
on acreage weights from the 2007 NRI. Cropped acreage
amounts, management of cropped acres, and conservation
treatments applied to the cropped acres were the only changes
simulated between the two survey periods. Impacts of all other
land uses were held constant across all analyses. Therefore,
this report provides a focused analysis on conservation gains
due to changes in conservation practices on cropped acres at
both the edge-of-field and instream scales.
The 2007 NRI indicates the Chesapeake Bay region has about
4.4 million acres of cultivated cropland. The estimated
cropped acreage was 4.28 million acres for the 2003-06 period
and 4.35 million acres for the 2011 survey, a difference of less
than 2 percent, and within the margins of error for both
surveys.
For purposes of this report, cropped acres include land in row
crops or close-grown crops, and hay and pasture in rotation
with row crops and close-grown crops. Cultivated cropland
does not include land that has been in hay, pasture, or
horticulture for 4 or more consecutive years. This report does
not consider conservation gains made between 2003-06 and
2011 on any other land use other than cultivated cropland.
The timing of this report is not coincident with a release of
information on land use by the USGS National Land Cover
Dataset (NLCD). Therefore, acreage estimates in this report
derived from both the National Census of Agriculture and
NLCD are identical to data applied in the original USDA
NRCS CEAP report for the Chesapeake Bay region (USDA
NRCS 2011; Appendix A).

Sampling and Modeling Approach
The assessment uses a statistical sampling and modeling
approach to estimate the environmental effects and benefits of
conservation practices (fig. 1.1). The following methods were
used:
 The 771 points sampled for the 2003-06 baseline are a
2
subset of sample points from the 2003 NRI. The 904
points sampled for the 2011 dataset are a subset drawn
from the 2007 NRI. These collections provide two
Information about the CEAP sample design is in “NRI-CEAP Cropland
Survey Design and Statistical Documentation,” available at
http://www.nrcs.usda.gov/technical/nri/ceap.
13
2

statistical samples selected from the same population of
points representing the diversity of soils and other
conditions for cropped acres in the Chesapeake Bay
region. All NRI sample points are linked to NRCS Soil
Survey databases and are linked spatially to climate
databases for these analyses;
 During both sampling periods, a farmer survey—the
NRI-CEAP Cropland Survey—was conducted at the
NRI sample points to determine what conservation
practices were in use and to collect detailed
information on farming practices;
 The field-level effects of the crop management and
conservation practices were estimated with a fieldscale physical process model—the Agricultural
Policy/Environmental eXtender (APEX)—which
simulates day-to-day farming activities, wind and water
erosion, loss or gain of soil organic carbon, and edgeof-field losses of water, soil, and nutrients; and
 The SWAT model (Soil and Water Assessment Tool)
was used to simulate non-point source loadings from
land uses other than cropland and to route instream
loads from one watershed to another.
Figure 1.1. Flow diagram of statistical sampling and modeling
approach used to simulate effects of conservation practices.

as in the 2003-06 baseline conservation condition
scenario. This scenario provides perspective on the
benefits of all conservation practices on cultivated
cropland and the loads that would impact the
Chesapeake Bay if no conservation practices were
adopted on cultivated cropland in the watershed
(Appendix B).
The approach captures the diversity of land use, soils, climate,
and topography from the two NRI sampling periods; accounts
for site-specific farming activities; estimates the loss of
materials at the field scale where the science is most
developed; and provides a statistical basis for aggregating
results to the regional and national levels. Both 2003-06 and
2011 scenarios relied heavily on four sources of conservation
practice information:
1. NASS CEAP Farmer Surveys;
2. National Resources Inventory (NRI);
3. Conservation Plans on file at NRCS district field
offices; and
4. Reports on Conservation Reserve Enhancement
Program (CREP) and Continuous Conservation
Reserve Program (CCRP) practices from USDA FSA
offices.
The CEAP sample was designed to enable reporting of results
for the four subregions (4-digit HUCs) within the Chesapeake
Bay region. The acreage weights were derived to approximate
total cropped acres by 4-digit HUC, as estimated by the full
2003 and 2007 NRI. The sample size restricts reliable and
defensible reporting of results to the subregion level. Acres
reported using the CEAP sample are estimated acres. Margins
of error for estimated acres used in this report are provided in
Appendix C.

Sampling: The NRI-CEAP Cropland Survey

The modeling strategy for estimating the long-term effects of
conservation practices in place during the benchmark survey
of 2003-06 as compared to long-term effects of conservation
practices in place in 2011 consists of three model scenarios
produced for each sample point:
1. The “2011 current conservation condition” scenario
provides model simulations that account for cropping
patterns, farming activities, and conservation practices
as reported in the 2011 NRI-CEAP Cropland Survey
and other sources;
2. The “2003-06 baseline conservation condition”
scenario provides model simulations that account for
cropping patterns, farming activities, and conservation
practices as reported in the 2003-06 NRI-CEAP
Cropland Survey and other sources; and
3. A “no-practice” scenario simulates the impact of not
adopting any conservation practices on croplands, but
holds all other model inputs and parameters the same

Analyses for cropped acres in this report, with the exception of
Table A1 in Appendix A and Chapter 5, are based on an NRICEAP Cropland Survey administered by the USDA National
Agricultural Statistics Service (NASS). Farmer participation
was voluntary, and the information gathered is confidential.
The survey content was specifically designed to provide
information on farming activities for use with a physical
process model to estimate field-level effects of conservation
practices.
Data from the original 771 sample points collected in 2003-06
provide a 2003-06 baseline condition against which to
compare the 2011 conservation condition, which was based on
analyses of 904 sample points collected in 2011.3 Of the 904
sample points visited in 2011, 364 had been sampled in the
2003-06 survey. The selection of these 364 points was purely
coincident in the random sample draw. These re-sampled
points were not preferentially selected, as that would violate
the principles of the statistical framework designed to
3

The surveys, the enumerator instructions, and other documentation can be
found at
http://www.nrcs.usda.gov/wps/portal/nrcs/detail/national/technical/nra/ceap/?c
id=nrcs143_014163

14

represent the Chesapeake Bay region. Selecting specific points
for resampling would not only violate the rigorous statistical
approach derived for NRI sampling, but would also shift the
focus of the report away from a regional analysis to
consideration of changes at those specific points. Intentional
point resampling might also lead to bias due to changing land
use, ownership, or tenure, and landowner/operator refusal to
participate in future surveys.
Relevant to this report, the survey obtained information on:
 crops grown in the survey year and the 2 previous
years, including double crops and cover crops;
 field characteristics, such as proximity to a water body
or wetland and presence of tile or surface drainage
systems;
 conservation practices associated with the field;
 crop rotation plan;
 application of commercial fertilizers (rate, timing,
method, and form) for crops grown in the survey year
and the 2 previous years;
 application of manure (source and type, nutrient
content, consistency, application rate, method, and
timing) on the field in the survey year and the 2
previous years;
 irrigation practices (system type, amount, and
frequency);
 timing and equipment used for all field operations
(tillage, planting, cultivation, and harvesting) in the
survey year and the 2 previous years; and
 general characteristics of the operator and the
operation.
In a separate survey, NRCS field offices provided information
on the practices specified in conservation plans for the
selected points in the region.
The 771 sample points from 2003-06 were a subset of a
national survey; data collection was necessarily a multi-year
effort due to the large number of sample points surveyed
nationally. In the fall of 2011 the Chesapeake Bay region was
the only area of the country where points were resampled,
enabling all points to be sampled in a single year. In each
sampling period, surveys were obtained for a statistically
appropriate, representative set of sample points. The final
CEAP sample was constructed by pooling the set of usable,
completed surveys from each survey period.

Modeling Changes, Issues, and Assumptions
APEX Model Version Changes
In this report, the 2003-06 and 2011 datasets were each
analyzed with the newest version of the APEX model,
APEXv1307. The APEX model is dynamic and APEX
developers continuously upgrade, amend, or add to its
modeling routines as new technologies emerge, as the science
of modeling natural processes improves, and as the needs of
new users introduce the model to new applications. The APEX
simulation results reported in the original USDA NRCS CEAP

report for the Chesapeake Bay region were analyzed with an
older version of APEX, APEXv2110 (USDA NRCS 2011).
Changes in the model versions contribute to the differences
between simulated results reported here for 2003-06 and those
reported in the original report for the same survey period
(USDA NRCS 2011).
The APEX model version 1307 used in this report
incorporates significant improvements in the routing of
surface and subsurface losses of nutrients and sediments from
one subarea to the next. The upgrades also enable
APEXv1307 to more accurately simulate the mitigating effects
of buffers, filters, and drainage water management on edge-offield losses. The new model version also better addresses
changing conservation practice needs and impacts due to
climate change predictions.

Erosion Equation Changes
The APEX component for water-induced erosion simulates
erosion caused by rainfall, runoff, and irrigation. APEX
contains eight equations capable of simulating rainfall and
runoff erosion: the Universal Soil Loss Equation (USLE);
Onstad-Foster modification of the USLE; the Revised
Universal Soil Loss Equation (RUSLE); RUSLE2; the
Modified Universal Soil Loss Equation (MUSLE); two
variations of MUSLE; and a MUSLE structure that accepts
input coefficients. In any given simulation, the model user
specifies only one of the equations to interact with other
APEX components.
This report uses the soil loss equation MUSLE, rather than
MUST (Modified Universal Soil loss equation-Theoretical),
which was used in the original Chesapeake Bay region CEAP
report (USDA NRCS 2011). This change contributes to
differences in model outputs used for analyses in each of the
two reports. This improvement is one reason that the
simulation results reported here for 2003-06 data differ from
those in the original report (USDA NRCS 2011).
In the original report, MUST, a theoretical version of the
modified universal soil loss equation (MUSLE), was the
erosion driver in APEX (USDA NRCS 2011). Compared to
MUSLE, the MUST equation tends to be more sensitive to
lower, less intense rainfall and runoff events, and generates
higher sediment yields for these events. MUST also tends to
deliver slightly more sediment for areas smaller than 40 acres.
This report, and future CEAP modeling efforts, will use the
MUSLE equation as the specified driver in APEX. MUSLE
enables better simulation of variable field dimensions and
sizes and provides better sediment yield estimates for more
significant events. MUSLE sensitivity also facilitates a better
determination of conservation treatment needs in relation to
the potential for increasing frequency and intensity of storm
events associated with climate change. However, the adoption
of MUSLE over MUST will tend to increase model estimates
of nutrient loss via surface runoff pathways and decrease
estimates of nutrients lost by subsurface pathways for all
climate scenarios.

15

Soil Data Changes
Each NRI CEAP point is linked to a soil map unit and the
interpretive soils information contained in the National Soil
Information System (NASIS). This database was designed to
support NRCS conservation planning needs and provide inputs
for the agency’s empirical erosion and engineering models.
NASIS data was not designed to meet the needs of many of
the process-based equations in the APEX model. The NASIS
data for soil properties is organized in layers which may be
composed of one or more soil horizons. The surface layers
have the properties of the first horizon throughout the layer.
Subsequent layers usually have the properties associated with
the most limiting horizon within the layer. Although useful in
empirical models, this approach creates unnatural boundaries
between soil layers, which, when input into process-based
models, unrealistically impact water flow, root growth, soil
organic carbon, pH, and bulk density. NASIS also tends to
overestimate soil carbon stores since the surface carbon
content is assumed to extend throughout the entire first soil
layer. Further, construction of the NASIS database is land-use
independent; therefore, some map unit values may not be
reflective of the land uses being modeled.
In the modeling process used in the original Chesapeake Bay
region CEAP report (USDA NRCS 2011), NASIS challenges
were addressed by adjusting the affected model parameters
and/or soil data inputs. The adjustments for the soil layer data
were obtained from the national soil characterization database,
which is derived from point data and organized by horizons. It
is the core data upon which the interpretive data in NASIS is
based. Adjustments applied to overcome the idiosyncrasies of
the NASIS data, such as the aforementioned issue with
artificial boundaries between soil layers, often disallowed
appropriate simulation of the effects of a limiting horizon
within a layer. To eliminate this problem, this and future
CEAP reports will use horizon-based data from the soil
characterization database or a close taxonomic representative
for each map unit. This improvement is one reason that the
simulation results in this report are slightly different for 200306 data than they were in the original report (USDA NRCS
2011).
All other interpretive data elements from NASIS for key
model inputs were used without modification. These
properties are for interpretations such as water table depth,
flood frequency, ponding, soil albedo, and other properties
used by some of the more empirical model relationships and
equations. These properties are also used for categorization
and data analysis.

Simulating the Effects of Weather
Weather is the predominant factor determining the loss of soil
and nutrients from farm fields; weather also plays a large role
in determining the effects of conservation practices. To
capture the effects of weather, each scenario was simulated
using 52 years of actual daily weather data. Thus, in this
report, the weather period provides data on 5 more years of

weather than were available during the analyses conducted for
the original Chesapeake Bay region CEAP report (USDA
NRCS 2011). This improvement in weather input data
contributes to slight differences in model outputs used for
analyses in each of the two reports.
The 52-year serially complete daily weather dataset for the
Chesapeake Bay region used in this report is the extent of the
data available from the National Climatic Data Center
(NCDC). Weather was recorded for the period 1960 to 2011,
including precipitation, temperature maximum, and
temperature minimum (Eischeid et al. 2000). These weather
station data were combined with the respective PRISM
(Parameter–Elevation Regressions on Independent Slopes
Model) (Daly et al. 1994) monthly map estimates to construct
daily estimates of precipitation and temperature (Di Luzio et
al. 2008). The same 52 years of weather data were applied to
both the 2003-06 and the 2011 datasets used in the APEX and
SWAT model simulations.
Annual precipitation over the 52 years ranged from 31 to 59
inches, and averaged about 42 inches for cropped acres in this
region. Annual precipitation varied spatially within the region
and between years. Reported estimates of the average effects
of conservation practices include consideration of
effectiveness in extreme weather years, such as during floods
and prolonged droughts, as captured in the natural variability
inherent in the 52-year weather record.
Throughout most of this report, model results are presented in
terms of the 52-year model runs, where weather is the only
input variable that changes from year to year. We did not
simulate actual losses expected to be observed during 2003-06
and 2011. Rather, model outputs predict average long-term
impacts of cropping patterns and conservation practices
reported to be in use during 2003-06 or 2011, assuming
weather patterns observed from 1960 to 2011 continue.

Watersheds
According to the U.S. Geological Survey’s hydrologic
accounting system, the Chesapeake Bay region includes four
subregions within the Mid-Atlantic Water Resource Region.
Each water resource region is designated with a 2-digit code,
and may be divided into 4-digit subregions, which may be
further subdivided into 8-digit watersheds, or Hydrologic Unit
Codes (HUCs) (USGS 1980).
Agricultural land use within each of the four subregions in the
Chesapeake Bay region is summarized in Table 1.1. The
Upper Chesapeake Bay subregion is the smallest subregion
and has the highest concentration of cropped acres (18
percent). About 11 percent of the largest subregion, the
Susquehanna River subregion, is maintained in cropped acres.
About three-fourths of the cropped acres in the region are in
the Susquehanna River and Upper Chesapeake Bay

16

subregions. The remaining two subregions, the Potomac River
Basin and the Lower Chesapeake Bay, have 8 and 5 percent of
their land base in cropped acres, respectively.
Estimates presented in this report for field-level effects of
conservation practices (chapters 2-4) are for the Chesapeake
Bay region, whereas estimates of instream water quality
effects (Chapter 5) are for the Chesapeake Bay watershed. The

Chesapeake Bay watershed excludes two 8-digit watersheds in
the Upper Chesapeake Bay subregion that drain to the Atlantic
Ocean (8-digit HUCs 02060010 and 02080110). The area that
includes these two watersheds is referred to as the Chesapeake
Bay region.

Table 1.1. Agricultural land use in the four subregions of the Chesapeake Bay region, 2011.
Subregion
code
0205
0206
0207
0208

Subregion name
Susquehanna River
Upper Chesapeake Bay
Potomac River Basin
Lower Chesapeake Bay
Total

Total
Acres (thousands)*
17,596
5,773
9,404
11,080
43,853

Cropped acres
(thousands)**
1,996
1,021
733
603
4,353

Percent of subregion
in cropped acres
11
18
8
5
10

Percent of
Chesapeake Bay
region’s cropped
acres
46
23
17
14
100

* Source: 2001 National Land Cover Database for the Conterminous United States (Homer et al. 2007)
** Source: 2007 National Resources Inventory. Does not include acres in long-term conserving cover (i.e., CRP general signups).

17

Chapter 2
Evaluation of Changes in Conservation
Practice Use—2003-06 to 2011
This study assesses the long-term effects of conservation
practices in use in the Chesapeake Bay region in 2011. It
further provides a 2011 conservation condition for the region,
against which changes in conservation gains and needs since
the 2003-06 benchmark survey may be gauged.
The original Chesapeake Bay region CEAP report applied
APEX to 2003-06 survey data to construct a baseline
conservation condition (USDA NRCS 2011). However, model
improvements and changes in soils and weather data made it
imperative that the 2003-06 data be reanalyzed for this report.
The 2003-06 and 2011 data have both been analyzed with the
most current version of the APEX model in order to provide a
revised baseline and to enable comparisons between the two
survey periods. Conservation practices evaluated include
structural, vegetative, and annual practices. Methods for
counting practices and thresholds were revised and improved
during the time between the two reports, which also
contributes to slightly different classifications between the two
reports.

The USDA NRCS promotes a comprehensive
conservation plan to address all resource
concerns, recognizing there are no single
practice solutions to address all resource
concerns and that some positive actions for one
resource concern may require additional efforts
to offset any negative impacts on another
resource. It is not the intent of this report to
parse or isolate the individual effects of each
conservation practice adopted. This report was
designed to assess the impacts of the
conservation systems in place at the time of the
two surveys. Simulation modeling was applied to
predict the anticipated long term impacts of
these practices if they are maintained into the
future.

Historical Context for Conservation Practice
Use
Conservation practices have long been used in the Chesapeake
Bay region. The first numeric goals for nutrient pollution
reduction were set in the 1987 Chesapeake Bay Agreement. In
the early 1990s the Chesapeake Bay region states prioritized
addressing the issue of nutrient management. Similarly, during
the 1990s, NRCS conservation efforts began to broaden from
prevention of soil erosion and enhancement of production
sustainability to encompass goals of reducing other
environmental impacts associated with agricultural
production, including reducing nutrient export from farm
fields. Although traditional conservation practices used to
control surface water runoff and erosion mitigate a significant
portion of potential nutrient losses, additional gains can be
achieved with adoption of appropriate practices designed for
nutrient management. For example, management strategies
that adopt the 4Rs (right rate, right timing, right method, and
right form of nutrient application) help achieve the avoidance
component of an Avoid, Control, Trap (ACT) conservation
system approach by minimizing nutrient losses to the
environment while maximizing availability of nutrients for
crop growth.
The Avoid, Control, Trap approach operates on the concept
that land managers adopt conservation systems that include
practices that Avoid excess tillage and nutrient application in
order to avoid sediment and nutrient losses. Some losses
cannot be avoided. In these instances practices such as terraces
or contouring help Control losses from the crop field.
Complementing the Avoid and Control components of the
system a third layer of conservation protection practices are
designed to Trap runoff or leaching losses from the production
area. The Trap practices includes filter strips, buffers, or in the
case of subsurface losses, drainage water management. Under
certain circumstances, wetlands may be constructed or
restored to trap both surface and subsurface losses.
Given the long history of conservation in the Chesapeake Bay
region, it is not surprising that nearly all cropped acres in the
region have evidence of some kind of conservation practice,
especially erosion control practices. Conservation practices
continue to make headway in important, measurable ways.
The most striking changes in conservation practice adoption
noted between the two survey periods include significant
increases in adoption of structural practices, conservation
tillage, and cover crops.
Structural and vegetative conservation practices (referred to
as “structural practices” herein), once implemented, are
usually kept in place for several years. Designed primarily for
erosion control, structural practices also mitigate edge-of-field
nutrient losses, providing both the controlling and trapping
benefits in a comprehensive Avoid, Control, Trap (ACT)
conservation plan. Structural practices include:
 in-field practices for water erosion control, divided into
two groups:
1. practices that control overland flow (terraces,
contour buffer strips, contour farming,
stripcropping, and contour stripcropping); and

18

2. practices that control concentrated flow (grassed
waterways, grade stabilization structures,
diversions, and other structures for water control);
 edge-of-field practices for buffering and filtering
surface runoff before it leaves the field (riparian forest
buffers, riparian herbaceous cover, filter strips, and
field borders);
 irrigation practices (irrigation method and irrigation
water management); and
 wind erosion control practices (windbreaks,
shelterbelts, crosswind trap strips, herbaceous wind
barriers, and hedgerow planting).
Annual conservation practices are management practices that
are an active part of the crop production system each year.
These practices are designed to promote soil quality, reduce
in-field erosion, and reduce the availability of sediment and
nutrients for transport by wind or water. They include:
 residue and tillage management;
 conservation crop rotations;
 nutrient management; and
 cover crops.

Structural Conservation Practices
Structural practices and conservation tillage have been
adopted on nearly all cropped acres in the region and typically
provide the control and trap components of the ACT system
approach. These practices were the primary drivers behind
reductions in sediment and nutrient losses from farm fields
between 2003-06 and 2011. Cover crop adoption was also a
significant driver of improved conservation management.
Cover crops, especially when used in combination with
conservation tillage or structural practices, had significant
impacts on reducing edge-of-field losses.
Data on structural practices associated with each sample point
were obtained from four sources:
1. The 2003-06 and 2011 NRI-CEAP Cropland Surveys,
which included questions about the presence of structural
practices: terraces, grassed waterways, vegetative buffers
(in-field), hedgerow plantings, riparian forest buffers,
riparian herbaceous buffers, windbreaks or herbaceous
wind barriers, contour buffers (in-field), field borders,
filter strips, critical area planting, grassed waterways,
and grade stabilization structures;
2. For fields with conservation plans, NRCS field offices
provided data on all structural practices included in the
plans;
3. The USDA Farm Service Agency (FSA) provided
practice information for fields enrolled in the Continuous
Conservation Reserve Program (CCRP) and
Conservation Reserve Enhancement Program (CREP) for
the following structural practices: contour grass strips,
filter strips, grassed waterways, riparian buffers (trees),
and field windbreaks (Rich Iovanna, USDA FSA,
personal communication, 2013); and
4. The 2003 and 2007 National Resources Inventory
(NRI) provided additional information for practices that
could be reliably identified from overhead photography
as part of the NRI data collection process. These
practices include contour buffer strips, contour farming,

contour stripcropping, field stripcropping, terraces,
crosswind stripcropping, crosswind trap strips,
diversions, field borders, filter strips, grassed waterways
or outlets, hedgerow planting, herbaceous wind barriers,
riparian forest buffers, and windbreak or shelterbelt
establishment.
The methods for identifying and developing modeling
techniques for the practices reported in these four sources
were improved in the interim between this and the original
Chesapeake Bay region CEAP report (USDA NRCS 2011).
These improvements, which altered practice counts in the
2003-06 data as compared to the original report, also required
that the 2003-06 and 2011 data both be analyzed under the
same constraints to enable comparison in this report.
Overall, adoption of structural practices for water erosion
control increased in the Chesapeake Bay region during the
interim between the two reports (table 2.1). In the Chesapeake
Bay region, between 2003-06 and 2011, the following changes
were noted on all cropped acres:
 Adoption of one or more structural practice for water
erosion control: 14 percentage point improvement,
increasing from occurring on 52 to 66 percent of
cropped acres;
 Cropped highly erodible land (HEL) acres treated with
one or more structural practice for water erosion
control: maintained 2003-06 conservation levels, at 70
percent;
 Cropped acres with adoption of two or more structural
practices for water erosion control: 16 percentage point
improvement, increasing from occurring on 17 to 33
percent of cropped acres; and
 Cropped HEL acres treated with two or more structural
practice for water erosion control: 6 percentage point
improvement, increasing from 23 to 29 percent of
cropped HEL acres.
Additionally, the surveys suggest a positive trend in adoption
of all three erosion control practices (overland flow,
concentrated flow, and edge-of-field mitigation) on all
cropped acres and cropped HEL acres. However, throughout
this report changes of 5 percent or less are considered to be
maintaining 2003-06 conservation levels.
Overland flow control practices are designed to slow the
movement of water across the soil surface, thereby reducing
both surface water runoff and sheet and rill erosion. NRCS
practice standards for overland flow control include terraces,
contour farming, stripcropping, in-field vegetative barriers,
and field borders. Overland flow control practices are the most
commonly implemented structural practice in the Chesapeake
Bay region. Between 2003-06 and 2011, the following
changes in overland flow control practice adoption were noted
(table 2.1):
 Overland flow control practice adoption on all cropped
acres: 7 percentage point improvement, increasing
from occurring on 38 to 45 percent of cropped acres;
 Overland flow control practice adoption on non-highly
erodible lands (NHEL): 13 percentage point

19

improvement, increasing from occurring on 29 to 42
percent of cropped NHEL acres; and
 Overland flow control practice adoption on highly
erodible lands (HEL): 6 percentage point decline,
decreasing from occurring on 55 to 49 percent of
cropped HEL acres.
For the purposes of this report tillage management, residue
management, and cover crop adoption are not analyzed as
solely overland flow control practices. However, these
practices are often used in conjunction with overland control
practices or in lieu of overland control practices, especially
when slopes are gentler or fields have complex contours,
which make the more engineered overland flow control
practices difficult to implement and maintain.
Concentrated flow control practices are designed to prevent
the development of gullies along flow paths within a field.
NRCS concentrated flow control practice standards include
grassed waterways, grade stabilization structures, diversions,
and water and sediment control basins. These practices are
typically installed to control both ephemeral and classic
gullies. Concentrated flow control practices used in
conjunction with overland flow control practices can have a
significant impact on sediment loss from cultivated cropland.
Between 2003-06 and 2011, the following changes in
concentrated flow control practice adoption were noted (table
2.1):
 Concentrated flow control practice adoption on all
cropped acres: 11 percentage point improvement,
increasing from occurring on 20 to 31 percent of
cropped acres;
 Concentrated flow control practice adoption on nonhighly erodible lands (NHEL): 10 percentage point
improvement, increasing from occurring on 13 to 23
percent of cropped NHEL acres; and
 Concentrated flow control practice adoption on highly
erodible lands (HEL): 8 percentage point improvement,
increasing from occurring on 35 to 43 percent of
cropped HEL acres.
Edge-of-field buffering and filtering practices are designed to
capture the surface runoff losses that are not mitigated by the
in-field conservation practices. NRCS practice standards for
edge-of-field mitigation include edge-of-field filter strips,
riparian herbaceous buffers, and riparian forest buffers.
CCREP and CREP buffer practices are included in this
category. Between 2003-06 and 2011, the following changes
in edge-of-field mitigation practice adoption were noted (table
2.1):
 Edge-of-field mitigation practice adoption on all
cropped acres: 17 percentage point improvement,
increasing from occurring on 14 to 31 percent of
cropped acres;
 Edge-of-field mitigation practice adoption on nonhighly erodible lands (NHEL): 21 percentage point
improvement, increasing from occurring on 15 to 36
percent of cropped NHEL acres; and
 Edge-of-field mitigation practice adoption on highly
erodible lands (HEL): 13 percentage point

improvement, increasing from occurring on 11 to 24
percent of cropped HEL acres.
Wind erosion is not a significant problem for most cropland
acres in this region. Wind erosion control practices are
generally found on acres on which crops such as vegetables
and melons are produced. Soils prone to wind erosion are
commonly found in the coastal plain region and tend to be
sandy or organic. Simulations show in 2003-06 and 2011, 93
and 96 percent of cropped acres had average annual wind
erosion rates less than 0.1 ton, respectively. The simulated
maximum average annual amount of soil lost per acre to wind
erosion under the 2003-06 baseline condition or 2011
conservation condition was 3.3 tons, but some acres in some
years can lose as much as 25 tons of soil to wind erosion. The
few acres in the region vulnerable to wind erosion due to their
combinations of cropping systems and soil types show
significant improvement with conservation practices. There
are so few of these acres in this regional context that analysis
of the benefits of wind erosion control practices are
impractical in the scope of this report. It should be noted,
however, that many of the practices intended to reduce
sediment loss to water erosion also have beneficial impacts on
reducing wind erosion losses.

Residue and Tillage Management Practices
Tillage type impacts conservation goals for several reasons:
 Tillage may provide better aeration and weed control,
but there are also potential negative effects, including
increased respiration rates, which contribute to soil
organic carbon loss, a decline in agroecological
diversity, and a decline in density of soil organisms;
 Tillage breaks up and buries plant residues, reducing
the soil surface protection against erosion;
 Tillage may compact the soil, decreasing soil health
and possibly stressing crop roots;
 Tillage operations require time and energy inputs,
which increase operational costs and increase carbon
dioxide emissions; and
 Periodic use of more intense tillage alternated with
conservation tillage can significantly reduce or
eliminate the positive effects of conservation tillage.
Simulations of the use of residue and tillage management
practices were based on the field operations and machinery
types reported in the NRI-CEAP Cropland Survey for each
sample point. The survey obtained information on the timing,
type, and frequency of each tillage implement used during the
previous 3 years, including the crop to which the tillage
operation was applied.
The Soil Tillage Intensity Rating (STIR) (USDA NRCS 2007)
was used to determine the soil disturbance intensity for each
crop at each sample point for each year included in the NRI
CEAP Cropland Surveys (2003-06 and 2011). STIR values are
a function of the kinds of tillage, the frequency of tillage, and
the depths of tillage. Analyzing the STIR values for each crop
year in conjunction with model output on long-term soil
organic carbon (SOC) trends elucidated the connections
between tillage intensity and carbon dynamics, including
carbon gain, maintenance, or loss.
20

Table 2.1. Structural conservation practices in use in the Chesapeake Bay region, 2003-06 and 2011.

Structural practice
category
Overland flow control
practices

Conservation practice
Terraces, contour buffer strips, contour
farming, stripcropping, contour
stripcropping, field border, in-field
vegetative barriers

2003-06
Percent
of NHEL

2011
Percent
of NHEL

2003-06
Percent
of HEL

2011
Percent
of HEL

2003-06
Percent
of all
cropped
acres

2011
Percent
of all
cropped
acres

29

42

55

49

38

45

Concentrated flow control
practices

Grassed waterways, grade stabilization
structures, diversions, other structures
for water control

13

23

35

43

20

31

Edge-of-field buffering and
filtering practices

Riparian forest buffers, riparian
herbaceous buffers, filter strips

15

36

11

24

14

31

One or more water erosion
control practice

Either overland flow, concentrated flow,
or edge-of-field practice

43

64

70

70

52

66

Two or more water erosion
control practices

Two practices, to include overland flow,
concentrated flow, or edge-of-field
practice

11

24

23

29

17

33

All three water erosion
control practices

Overland flow, concentrated flow, and
edge-of-field practice

2

6

4

9

2

7

Note: In the 2003-06 survey there were an estimated 1.87 million HEL acres (44 percent). The subset of NRI points for the 2011 survey had 1.75 million HEL acres (40
percent); a difference within the margins of error. The full set of 2007 NRI points for cropped acres in this region indicate 40 percent of the acres are HEL. Soils are
classified as HEL if they have an erodibility index (EI) score of 8 or higher. A numerical expression of the potential of a soil to erode, EI considers the physical and
chemical properties of the soil and climatic conditions where it is located. The higher the index, the greater the investment needed to maintain the sustainability of the
soil resource base if intensively cropped.

Tillage management and conservation tillage adoption was
assessed on a crop by crop basis for each cropping system.
Each crop was classified according to its average annual Soil
Tillage Intensity Rating (STIR). For the purpose of these
analyses, crops produced with a STIR rating exceeding 80
were considered conventionally tilled, crops produced with a
STIR value between 20 and 80 were considered mulch-till,
and crops with a STIR value less than 20 were considered notill. These classifications differ from those used in the 2003-06
assessment and reflect improvements in the NRCS residue and
tillage management practice standards. Previously, crops
produced with a STIR value of 30 or less were considered notill and conventional tillage was determined by STIR values
greater than 100.
The benefits of adopting less intense tillage are realized only
with consistent use of reduced tillage for all crops in a
rotation. Many farmers will employ “rotational tillage”, in
which they apply one type of tillage on one crop and use a
different intensity of tillage on the succeeding crop. Use of
conventional tillage on one crop in a rotation can diminish or
negate many of the positive aspects associated with adoption
of conservation tillage, especially no-till. However, no-till is
not the tillage solution for all crops on all acres. In particular,
appropriate manure management requires a means of
incorporation in the application method. This can generally be
accomplished with some form of mulch-tillage or specially
developed low impact methods of manure incorporation.

To assess the conservation tillage adoption trends between the
two survey periods the following classifications were
developed for cultivated cropland in the Chesapeake Bay
region:
 Continuous Conventional Tillage: all crops
conventionally tilled (STIR >80);
 Seasonal Conventional Tillage: at least one crop in
rotation conventionally tilled and at least one crop
conservation tilled;
 Continuous Mulch-tillage: all crops in rotation mulchtilled, with STIR values for each crop between 20 and
80;
 Seasonal No-till: at least one crop produced with no-till
(STIR <20) and no crop in rotation conventionally
tilled; and
 Continuous No-till: all crops in rotation are no-till and
produced with STIR values <20.
Adoption of conservation tillage, especially no-till, made rapid
gains in the Chesapeake Bay region between 2003-06 and
2011 (fig. 2.1). Findings related to tillage practice changes on
cultivated cropland between 2003-06 and 2011 include:
 Management using either continuous or seasonal
conventional tillage decreased by half, dropping from
being practiced on 44 to 21 percent of acres;
 Acres on which continuous conventional tillage was
applied decreased by half, dropping from 13 to 6
percent of acres;

21

 Seasonal use of conventional tillage declined by half,
dropping from being practiced on 31 to 15 percent of
acres;
 Use of some form of conservation tillage without any
conventional tillage increased from being in use on 56
to 79 percent of acres;
 Management using either continuous or seasonal notill, without the use of conventional tillage on any crop,
increased from occurring on 50 to 75 percent of acres;
 Acres on which seasonal no-till was applied nearly
doubled, increasing from 12 to 21 percent of acres; and
 Use of continuous no-till increased from 38 to 54
percent of acres.
The decreased use of conventional tillage at any point in the
rotation enables the retention of more residue, which protects
the soil and associated nutrients from being lost to wind and
water erosion. The increased residue associated with adopting
conservation tillage over conventional tillage not only protects
the soil surface from erosion, but also improves infiltration,
increases water availability for the crops, and builds soil
health.

The effectiveness of conservation tillage and structural erosion
control practices are both improved by inclusion of the other
in a comprehensive conservation plan. The use of conservation
tillage without structural practices and the use of structural
practices without conservation tillage both declined between
2003-06 and 2011 (table 2.2). Adoption of suites of
conservation practices that combine conservation tillage and
structural practices now occurs on a majority of the cropped
acres in the region. Between 2003-06 and 2011, the following
changes were noted on cropped acres in the Chesapeake Bay
region (table 2.3):
 Adoption of some kind of water erosion control
practice, either reduced tillage, structural practice(s), or
both: 10 percentage point improvement, increasing
from occurring on 87 to 97 percent of cropped acres;
and
 Adoption of some kind of water erosion control
practice and conservation tillage: 24 percentage point
improvement, increasing from occurring on 39 to 63
percent of cropped acres.

Percent of cultivated cropland in each
tillage class

Figure 2.1. Changes in tillage management, as calculated from average annual STIR values for each crop in the rotation in the
4
Chesapeake Bay region, 2003-06 and 2011.
60
50
40
30
20
10
0

CCT

SCT

CMT

SNT

CNT

2003-06

13

31

6

12

38

2011

6

15

4

21

54

Note: CCT = continuous conventional tillage; SCT = seasonal conventional tillage; CMT = continuous mulch-tillage; SNT = seasonal no-till; CNT = continuous no-till.

4
Average Soil Tillage Intensity Rating (STIR) over all crop years in the rotation less than or equal to 20 is considered no-till; STIR less than or equal to 80 is
considered mulch-till; and a STIR value greater than 80 is considered conventional tillage.

22

Table 2.2. Conservation tillage, including no-till and mulch-till, applied singularly or in conjunction with structural practices in the
Chesapeake Bay region, 2003-06 and 2011.

Combination of conservation practice

2003-06
Acres
(thousands)

2011
Acres
(thousands)

Acres
(percent)

Acres
(percent)

Conservation tillage only*

1,477.1

35

1,164.3

27

Conservation tillage with structural practices*

1,660.3

39

2,755.6

63

Structural practices only

602.6

14

296.6

7

No water erosion control treatment

539.9

13

136.9

3

4,279.9

100

4,353.4

100

Total

Note: Percent may not add to totals because of rounding.
* NRCS practice standards for residue and tillage management have been revised since the publication of the original report (USDA NRCS 2011). Average Soil Tillage
Intensity Rating (STIR) over all crop years in the rotation must be less than or equal to 20 for no-till; average STIR less than or equal to 80 is considered mulch-till; and
a STIR value greater than 80 is considered conventional tillage. These STIR criteria are different from those applied in the original report, under which a value of 30 or
less was classified and no-till and 100 or greater was classified as conventional tillage.

Table 2.3. Cropped acres in the Chesapeake Bay region, 2003-06 and 2011.

Cropping System

2003-06
Acres
(thousands)

Corn only

690

Acreage
(percent)

2011
Acres
(thousands)

16.1

364

Acreage
(percent)
8.4

Soybean only

161

3.8

128

2.9

Corn-Soybean

1,175

27.4

880

20.2

Corn with wheat or close-grown crop

272

6.4

336

7.7

Soybean-Wheat

125

2.9

120

2.8

7

0.2

45

1.0

Corn-Soybean with wheat or close-grown crop

798

18.6

1,252

28.7

Vegetables or Tobacco, excluding hay

143

3.3

209

4.8

Hay and any other

627

14.7

701

16.1

282

6.6

318

7.3

Soybean with close-grown crop

Remaining mix of crops
Totals

4,280

4,353

Note: The difference between 2003-06 and 2011 cropping systems represent land-use changes in the 4-year time period between the two surveys. The 200306 estimates are based on acreage weights derived from the 2003 NRI, while the 2011 estimates are based on acreage weights derived from the 2007 NRI.
Estimates for 2011 cropped acres do not account for cover crops applied to the rotations, while the 2003-06 estimates do account for cover crops applied to
the rotations.

Conservation Crop Rotation
Conservation crop rotation (NRCS practice code 328) involves
growing various crops on the same piece of land in a planned
sequence to deliver conservation benefits. For example, this
sequence may contribute to development of soil organic
carbon pools by growing high residue-producing crops such as
corn or wheat in rotation to offset the effects of growing low
residue-producing crops, such as vegetables or soybeans. The
rotation may also involve growing forage crops or cover crops
in rotation with various field crops, which may increase the
multi-functionality of the land and diversify the farmer’s
economic base while also conserving soil. Increasing adoption
of high residue crop rotations in the Chesapeake Bay region

between 2003-06 and 2011 reflects the increasing
diversification of cropping systems, concurrent with a
reduction in low residue monocultures and simple cornsoybean rotations (table 2.3). This positive trend in
conservation crop rotation adoption has markedly improved
annual residue scores in the region (fig. 2.2). Cover crop
adoption has become an important complementary practice to
conservation crop rotation. However, it should be noted that
cover crop adoption is only one part of an effective
conservation management plan. To produce consistent and
beneficial results, conservation management plans must be
reevaluated and applied appropriately and consistently.

23

Percent of cultivated cropland in each
residue class

Figure 2.2. Average annual residue scores in the Chesapeake Bay region, 2003-06 and 2011.
60
50
40
30
20
10
0

Score <1

Score 1 to 2

Score 2 to 3

Score 3 to 4

2003-06

2

51

37

10

2011

2

35

37

26

To allow numerical comparison of the residue level of various
crop rotations, a simple scoring system was developed using
relative values to represent a crop’s residue production value.
Hay crops scored the highest possible score of 4, as they are
typically established for two or more years and hay crop
residue confers excellent erosion protection. High residue
annual crops like corn and wheat have a score of 2 and low
residue crops, such as silage, soybeans, or cotton, score only 1.
Vegetable crop management tends to provide low residue and
include heavy tillage following removal of the entire plant.
Such cropping systems score 0.25, as the residue contribution
of four such crops in a year would be required to provide the
conservation value derived from one low residue crop.
On a given acre, total points for all the crops in rotation,
including cover crops, are summed and divided by the length
of the rotation. For example, the 1.5 corn-soybean rotation
score can be increased to 2.5 via the addition of a cover crop
between the corn and soy. Use of a cover crop after each
commodity crop would raise the rotation score to 3.5.
Changing crop rotations and adoption of conservation
practices that increase residue scores occurred between 200306 and 2011 (fig. 2.2). The acreage maintained as
monocultures of corn or soybeans or a simple corn-soybean
rotation declined from 47 to 32 percent of cropland acres
between 2003-06 and 2011 (table 2.2). Crop rotations
increased in complexity, primarily due to the addition of
wheat or other close-grown winter annuals, including cover
crops. Crop diversification improved residue scores between
2003-06 and 2011. During that interim, acreage with scores
between 1 and 2, typical of a corn-soybean rotation, declined
from 51 percent to 35 percent of acres. This 16 percentage

point decline in acreage scoring 1 to 2 was accompanied by a
16 percentage point increase in acres scoring 3 to 4. The
increase is in large part due to the increase in cover crop
adoption and inclusion of winter annual small grains.

Cover Crops and Winter Cover
Cover cropping consists of planting grass, small grains, or
legumes between primary crop intervals, enabling farmers to
better manage nutrient inputs, enhance soil quality, and/or
reduce soil erosion. In the context of this report cover crops
are considered a unique subset of winter cover. Cover crops
are planted when principal crops are not growing, which may
include, but is not limited to, winter months. Cover crops are
not planted with the intent to harvest and are generally
terminated by tillage or herbicide application prior to maturity.
Winter cover includes crops that may be grazed and/or
harvested for grain, hay, or both. Cover crops and
conservation crop rotations that include winter annuals are
critical to protecting soil and water quality in the Chesapeake
Bay region. Local emphasis on these practices has helped
make significant improvements towards reducing the impacts
of cropped acres on the Chesapeake Bay. The benefits of
including cover crops in crop rotations most notably include
reduction in runoff losses and erosion (table 2.4). Simulations
suggest that increased adoption of winter cover observed in
2011 reduced 2003-06 loss rates by 37 percent for sediment,
28 percent for nitrogen via surface water, 18 percent for
nitrogen via subsurface flow, 29 percent for phosphorus, and
46 percent for carbon (table 2.4).
Conservation crop rotation has contributed to more acres
being protected by vegetation during the late fall and winter
months. Some rotations also promote soil health and water
quality by reducing nutrient input requirements for crop

24

production or by utilizing “leftover” nutrients from previous
crops, making them less available to losses via erosion. Cover
crops and winter cover also contribute to soil quality by
converting atmospheric carbon into plant tissue, which
eventually becomes soil organic matter and contributes to soil
carbon pools. Additionally, depending on management, cover
crops may provide pollinator or wildlife benefits, including
habitat and food production.
Table 2.4. Reduction in specified losses due to adoption of
winter cover in at least part of the crop rotation, between
2003-06 and 2011 conditions.
Loss Category
Sediment

Reduction (percent)
37

Nitrogen via Surface Water

28

Nitrogen via Subsurface Water

18

Total Phosphorus

29

Carbon

46

Benefits of cover cropping specific to individual conservation
crop rotation practices could not be assessed as cover crops
were often adopted as part of a suite of conservation practices
in a comprehensive conservation plan. Benefits of cover crops,
conservation crop rotations, conservation tillage, structural
practices, and nutrient management strategies are often
intertwined.
The major distinction between cover crops and other types of
winter cover is the approach to nutrient management. Winter
annuals grown for grain are generally “top dressed” with
nitrogen in early spring to ensure availability of nutrients
necessary for grain production. When appropriately applied to
an actively growing crop, the majority of these nutrients tend
to be taken up quickly by the plants, so that the fertilizer
application usually has very little impact on offsite water
quality.
The presence or absence of cover crops and winter cover was
determined from farmer responses in the NRI-CEAP Cropland
Survey. The following criteria were used to identify use of a
cover crop and to differentiate winter cover from cover crops:
 Winter cover is limited to close-grown crops grown
over the winter months and subsequently harvested for
hay or grain or both. These crops may be grazed.
 A cover crop is not harvested as a principal crop. If it is
harvested, it must have been specifically identified in
the NRI-CEAP Cropland Survey as a cover crop
harvestable for an acceptable purpose (such as biomass
removal or use as mulch or forage material). 5
 Spring-planted cover crops are inter-seeded into a
growing crop or are followed by the seeding of a
summer or late fall crop that may be harvested during
that same year or early the next year.

 Late-summer-planted cover crops are followed by the
harvest of another crop in the same crop year or the
next spring.
 Fall-planted cover crops are followed by the spring
planting of a crop for harvest the next year.
Some cover crops are planted for soil protection during
establishment of spring crops such as melons, spinach, and
potatoes. Early-spring cover crop vegetation protects both soil
and young crop seedlings.
In recent years both state and Federal programs have
contributed to significant increases in voluntary adoption of
cover crops and winter cover in the Chesapeake Bay region.
Cover crop adoption rose dramatically in the subregions
encompassing Maryland (Upper Chesapeake Bay–subregion
0206 and the Potomac River Basin–subregion 0207). Between
2003-06 and 2011 cropped acreage receiving cover crops at
some point in the rotation in the Upper Chesapeake Bay
subregion more than tripled, increasing from 14 to 65 percent
of cropped acres. During the same interim, acreage receiving
cover crops at some point in the rotation in the Potomac River
Basin subregion nearly tripled as well, increasing from 17 to
62 percent of cropped acres (table 2.5).
Between 2003-06 and 2011, the following trends related to
cover crops and winter cover were noted in the Chesapeake
Bay region’s cultivated cropland (tables 2.5 and 2.6):
 Annual use of cover crops: 13 percentage point
improvement, increased from occurring on 5 to 18
percent of cropped acres;
 Annual use of winter cover, which protects the soil
over the winter months: 14 percentage point
improvement, increased from occurring on 3 to 17
percent of cropped acres;
 Cover crops used at some point in the crop rotation: 40
percentage point improvement, increased from
occurring on 12 to 52 percent of cropped acres; and
 Cropped acres including winter cover as part of the
crop rotation, which protects the soil over the winter
months: 18 percentage point improvement, increased
from occurring on 47 to 65 percent of cropped acres.
The increased use of winter annuals in the crop rotation may
be attributed to market forces (e.g., higher wheat prices) and
the flexibilities of some of the region’s cover crop programs,
which allow farmers to opt to manage their cover crop for
grain harvest in return for a reduced cost share on the cover
crop. State programs also continue to contribute to winter
cover and cover crop adoption. For example, the Maryland
Department of Agriculture cover crop program reported
414,000 acres were planted to cover crops in 2012.

5

Except for the 2003 survey, the questionnaire allowed the respondent to list
the purpose for which a crop was grown, including cover crop. This
information was not a reliable indicator of a cover crop for conservation
purposes for all sample points, based on other information in the survey on
crops planted and field operations.

25

Table 2.5. Percent of cropped acres that apply cover crops as a conservation practice in the Chesapeake Bay region by subregion,
2003-06 and 2011.
Subregion Name:
Cover crop strategy

Susquehanna River
Basin (0205)
2003-06
2011
percent
percent

Upper Chesapeake
Bay (0206)
2003-06
2011
percent
percent

Potomac River
Basin (0207)
2003-06
2011
percent
percent

Every year

5

13

4

26

10

26.

2 of every 3 years

2

5

2

20

<1

Every other year
Less than every other
year

0

0

1

0

0

3

17

7

20

91

65

86

35

None

Lower Chesapeake
Bay (0208)
2003-06
2011
percent
percent
3

13

16

2

0

<1

7

20

83

38

2003-06
Chesapeake
Bay Region

2011
Chesapeake
Bay Region
5

18

23

2

13

0

<1

0

1

33

4

20

93

30

88

48

Table 2.6. Percent of cropped acres that utilize winter cover as part of their crop rotation in the Chesapeake Bay region by subregion,
2003-06 and 2011.
Subregion Name:
Winter cover strategy
Every year
2 of every 3 years

Susquehanna River
Basin (0205)
2003-06
2011
percent
percent

Upper Chesapeake
Bay (0206)
2003-06
2011
percent
percent

Potomac River
Basin (0207)
2003-06
2011
percent
percent

Lower Chesapeake
Bay (0208)
2003-06
2011
percent
percent

2003-06
Chesapeake
Bay Region

2011
Chesapeake
Bay Region

5

14

2

20

4

24

2

10

3

17

15

18

5

16

12

17

10

8

11

16

Every other year
Less than every other
year

6

9

16

16

9

11

15

28

11

14

24

16

23

21

19

22

16

21

22

19

None

49

42

55

27

56

25

57

33

53

35

Irrigation Management Practices
In the Chesapeake Bay region, irrigation applications are
sometimes used to supplement natural rainfall. Irrigation is
performed with either a gravity system or a pressure system.
Gravity systems utilize gravitational energy to move water
from higher elevations to lower elevations, such as moving
water from a ditch at the head of a field, across the field to the
lower end. Pumps are most often used to create the pressure in
pressurized systems, and the water is delivered through
nozzles or emitters.
Proper irrigation involves efficient use of water such that plant
water stress is alleviated and minimal water is lost. The
widespread trend of converting gravity irrigation systems to
pressure systems and the advent of pressure systems in rainfed agricultural areas has reduced the volume of irrigation
water lost to deep percolation and end-of-field runoff, but has
increased the volume of water lost to evaporation due to the
sprinkling process associated with most pressure systems.
Between 2003-06 and 2011, irrigated acreage in the
Chesapeake Bay region increased from 209,000 acres to
261,000 acres. Pressure systems were used on 97 percent of
irrigated acres in the region during both survey periods. The
most common and efficient pressure systems, center-pivot or
linear move systems with low pressure spray, were in use on
34 percent of irrigated acres in 2003-06 and 46 percent of

irrigated acres in 2011. Center-pivot or linear move systems,
with less efficient impact sprinklers, declined from being in
use on 44 to 28 percent of irrigated acres between 2003-06 and
2011.
As of 2011, low flow irrigation systems such as drip, trickle,
or micro emitters were used on 13 percent of the irrigated
acres in the region. Irrigated acreage on which highly efficient,
state of the art systems (e.g., center pivot or linear move
systems with low pressure, near-ground emitters, or low flow
systems such as drip and trickle) were applied increased from
39 to 60 percent of cropped acres between 2003-06 and 2011.

Nutrient Management Criteria
Nitrogen and phosphorus are essential inputs for profitable
and sustainable crop production. Farmers supply these
nutrients to the land with commercial fertilizers and/or
manure. A large portion of the nutrients applied to the land are
taken up by the crops and removed from the fields at harvest.
However, crops do not use all of the applied nutrients; some
are lost to the environment through various pathways,
including leaching, erosion, and, in the case of nitrogen,
volatilization. When edge-of-field losses are combined with
naturally occurring nutrients, nutrients from past losses, or
nutrients from other sources, they can contribute to offsite
water quality problems.

26

Nutrient management is an active management practice and
plays an important role in the Avoid, Control, Trap (ACT)
conservation system approach. Nutrient management planning
should be used in conjunction with conservation practices
designed to control and trap nutrients and sediment.
Appropriate nutrient application management must be utilized
each year and on each crop in the rotation in order for the
conservation benefits of the 4Rs (the right rate, the right
timing, the right method, and the right form) to persist in the
region.
Sound nutrient management systems can minimize nutrient
losses from the agricultural management zone while providing
adequate soil fertility and nutrient availability to ensure
realistic yields. The agricultural management zone is defined
as the zone surrounding a field that is bounded by the bottom
of the root zone, edge of the field, and top of the crop canopy.
Nutrient management systems are tailored to address the
specific cropping system, nutrient sources, and site
characteristics of each field. However, the 4Rs provide basic
criteria for appropriate application of commercial fertilizers
and manure:
1. Apply nutrients at the right rate based on soil and
plant tissue analyses and realistic yield goals.
2. Apply nutrients at the right time to supply the crop
with nutrients when the plants have the most active
uptake and biomass production; avoid applying
nutrients when adverse weather conditions can result in
large losses of nutrients from the agricultural
management zone.
3. Apply nutrients using the right method of application
for the nutrient source being applied in order to enable
rapid, efficient plant uptake and reduce the exposure of
nutrient material to forces of wind and water.
4. Apply the right form of commercial fertilizer and/or
manure, with compositions and characteristics that
resist nutrient losses from the agricultural management
zone.
Depending on the field characteristics, nutrient management
techniques can be coupled with other conservation practices
such as conservation crop rotations, cover crops, residue
management practices, and structural practices to minimize
the potential for nutrient losses from the agricultural
management zone. Even though nutrient transport and losses
from agricultural fields cannot be completely eliminated, they
can be minimized with careful ACT conservation planning
and implementation of complementary conservation practices.
Determination of appropriate nutrient management practices
was based on information on the rate, timing, and method of
application for manure and commercial fertilizer, as reported
by the producer in the NRI-CEAP Cropland Survey. The
appropriateness of nutrient form was not evaluated due to
insufficient survey data. Although it is not discussed in this
report, the appropriateness of nutrient form should be
considered in conjunction with rate, timing, and method of
nutrient application in the development of sound nutrient
management plans.

The following criteria enable comparison of changes in
conservation benefits due to changing nutrient management
plans between 2003-06 and 2011. Criteria used here to classify
nutrient management practices, while consistent with NRCS
standards, do not necessarily represent the best possible set of
nutrient management practices for these acres. These nutrient
management criteria are intended to represent practice
recommendations commonly found in comprehensive nutrient
management conservation plans. The following criteria were
used to identify appropriate rate, timing, and method of
nutrient applications for each crop or crop rotation.

Appropriate Rate Criteria

 Nitrogen application rate criteria apply to each crop in
the rotation.
 The rate of nitrogen application, including the sum of
commercial nitrogen fertilizer and manure nitrogen
available for crops in the year of application, is—
• less than 1.4 times the amount of nitrogen removed
in the crop yield at harvest for each crop, except for
cotton and small grain crops;
• less than 1.6 times the amount of nitrogen removed
in the crop yield at harvest for small grain crops
(wheat, barley, oats, rice, rye, buckwheat, emmer,
spelt, and triticale); and
• less than 60 pounds of nitrogen per bale of cotton
harvested.
 Phosphorus application rate criteria apply to the full
crop rotation to account for infrequent applications
intended to provide phosphorus for multiple crops or
crop years, which is often the case with manure
applications.6
 The rate of phosphorus application, including both
manure and commercial fertilizer, summed over all
applications and crops in the rotation is less than 1.2
times the amount of phosphorus removed in the crop
yields at harvest summed over all crops in the rotation.

It should be noted that in the analysis of the 2003-06 survey in
the original Chesapeake Bay region CEAP report, the
phosphorus application rate threshold criterion was 1.1 times
the phosphorus removed at harvest and for the 2011 analysis
this value has been increased to 1.2 (USDA NRCS 2011). This
change was necessary due to improvements in the phosphorus
adsorption/desorption routine in APEXv1307. The 1.1
criterion produced extensive phosphorus stress and
significantly reduced yields in the simulation. The incremental
increase of simulated phosphorus rate application to 1.2 times
the amount of phosphorus removed in the crop at harvest
reduced phosphorus stress and maintained expected yields.

Appropriate Timing Criteria
Timing application close to planting supplies nutrients closer
to the time when the crop needs them, thereby reducing the
risk of loss. The analyses in the original report required proper
timing of all commercial fertilizer and manure applications to
be within 21 days before or after planting. In the analyses for
6

For this reason the appropriateness of rate of application for phosphorus
cannot be analyzed in the same manner used for nitrogen, resulting in slightly
different information being presented in tables 2.7 and 2.8.

27

this report the criteria was changed to evaluate the length of
time between the application dates only prior to planting. The
change was made to eliminate the erroneous classification of
acres where spring applications of nutrients were appropriately
applied to winter annuals outside of the 42-day window.

Appropriate Method Criteria
To meet nutrient application method criteria, application of
commercial fertilizer or manure must include some form of
incorporation, banding, spot treatment, or foliar application.

Survey Results: Nutrient Management
Practices
Survey results suggest that although some conservation gains
achieved between 2003-06 and 2011 could be attributed to
improved nutrient management practices, there is still ample
opportunity to improve nutrient management planning in the
region. Differences between values reported here as compared
to those in the 2011 report are in large part attributable to
improvements in the APEX model related to nutrient cycles
for both nitrogen and phosphorus. Interpretation of application
timing values also differs between the two reports due to a
change in evaluation criteria.

Nitrogen – Appropriate Rate
Between 2003-06 and 2011, the following trends related to
nitrogen application rates were noted in the Chesapeake Bay
region’s cultivated cropland (table 2.7):
 Nitrogen receiving acres on which nitrogen application
rate criteria were met for all crops in rotation: 9
percentage point decline, decreased from 32 to 23
percent of cropped acres;
 Nitrogen receiving acres on which nitrogen application
rate criteria were met for some but not all crops in
rotation: 17 percentage point improvement, increased
from 54 to 71 percent of cropped acres;
 Nitrogen receiving acres on which nitrogen application
rate criteria were not met on any crop in the rotation: 7
percentage point improvement, decreased from 13 to 6
percent of cropped acres; and
 Cropped acres with no nitrogen application:
maintained 2003-06 conservation levels (5 and 2
percent of cropped acres in 2003-06 and 2011,
respectively).
When rate criteria were applied by crop rather than by
management over the entire rotation, adherence to appropriate
nitrogen application rates maintained conservation levels
achieved in 2003-06 (52 and 55 percent of crops in 2003-06
and 2011, respectively).
Commercial fertilizer was the only source of nitrogen for 2.5
and 2.2 million cropped acres in 2003-06 and 2011,
respectively. Between 2003-06 and 2011, the following trends
related to nitrogen application rates were noted in the
Chesapeake Bay region’s cultivated cropland acres receiving
commercial fertilizer as their sole nitrogen source, with no
manure inputs (table 2.7):
 Commercial nitrogen receiving acres (no manure
inputs) on which nitrogen application rate criteria were

met on all crops in rotation: 7 percentage point decline,
decreased from 42 to 35 percent;
 Commercial nitrogen receiving acres (no manure
inputs) on which nitrogen application rate criteria were
met on some but not all crops in rotation: 10
percentage point improvement, increased from 52 to 62
percent; and
 Commercial nitrogen receiving acres (no manure
inputs) on which nitrogen application rate criteria were
not met on any crop in the rotation: maintained 200306 conservation levels (6 and 3 percent of cropped
acres in 2003-06 and 2011, respectively).
The most significant changes to nitrogen application rates
occurred on acreage on which manure is applied to one or
more of the crops in rotation, either as a sole nutrient source or
in conjunction with commercial fertilizers. Between 2003-06
and 2011, the practice of applying manures as a nitrogen
source increased from occurring on 38 percent (1.6 million
acres) to 48 percent (2.1 million acres) of cropped acres in the
region. Between 2003-06 and 2011, the following trends
related to nitrogen application rates were noted in the
Chesapeake Bay region’s cultivated cropland acres receiving
manure inputs as a nitrogen source, with or without additional
commercial fertilizer inputs (table 2.7):
 Manured acres on which nitrogen application rate
criteria were met on all crops in rotation: 8 percentage
point decline, decreased from 17 to 9 percent;
 Manured acres on which nitrogen application rate
criteria were met on some but not all crops in rotation:
23 percentage point improvement, increased from 59 to
82 percent; and
 Manured acres on which nitrogen application rate
criteria were not met on any crop in the rotation: 15
percentage point improvement, decreased from 24 to 9
percent.

Nitrogen – Appropriate Timing
Between 2003-06 and 2011, the following trends related to
nitrogen application timing were noted in the Chesapeake Bay
region’s cultivated cropland (table 2.7):
 Nitrogen receiving acres on which nitrogen application
timing criteria were met for all crops in rotation: 14
percentage point decline, decreased from 50 to 36
percent of cropped acres;
 Nitrogen receiving acres on which nitrogen application
timing criteria were met for some but not all crops in
rotation:16 percentage point improvement, increased
from 34 to 50 percent of cropped acres; and
 Nitrogen receiving acres on which nitrogen application
timing criteria were not met on any crop in the
rotation: maintained 2003-06 conservation levels (11
percent in both surveys).
Between 2003-06 and 2011, the following trends related to
nitrogen application timing were noted in the Chesapeake Bay
region’s cultivated cropland acres receiving commercial
fertilizer as their sole nitrogen source, with no manure inputs
(table 2.7):
 Commercial nitrogen receiving acres (no manure
inputs) on which nitrogen application timing criteria

28

were met on all crops in rotation: 10 percentage point
decline, decreased from 69 to 59 percent;
 Commercial nitrogen receiving acres (no manure
inputs) on which nitrogen application timing criteria
were met on some but not all crops in rotation: 10
percentage point improvement, increased from 15 to 25
percent; and
 Commercial nitrogen receiving acres (no manure
inputs) on which nitrogen application timing criteria
were not met on any crop in the rotation: maintained
2003-06 conservation levels (9 and 13 percent of
cropped acres in 2003-06 and 2011, respectively).
Between 2003-06 and 2011, the following trends related to
nitrogen application timing were noted in the Chesapeake Bay
region’s cultivated cropland acres receiving manure inputs as
a nitrogen source, with or without additional commercial
fertilizer inputs (table 2.7):
 Manured acres on which nitrogen application timing
criteria were met on all crops in rotation: 6 percentage
point decline, decreased from 18 to 12 percent;
 Manured acres on which nitrogen application timing
criteria were met on some but not all crops in rotation:
12 percentage point improvement, increased from 66 to
78 percent; and
 Manured acres on which nitrogen application timing
criteria were not met on any crop in the rotation: 6
percentage point improvement, declined from 16 to 10
percent of manured cropped acres.
Between 2003-06 and 2011, manure application expanded
from occurring on 38 to 48 percent of cropped acres (fig. 2.3).
Manure was applied to these acres as part of their nutrient
management plan, either as the sole nutrient source, or in
conjunction with commercial fertilizers. The decline in use of
the more optimal 21 days out manure application timing for
all crops in rotation may be the result of traditional manure
users applying manure to more acres and requiring more
management time to get it spread. Additionally, it is possible
new manure users are adjusting to managing a new nutrient
source. The finding that more acres are receiving appropriately
timed manure applications on some crops in rotation is a
positive sign.

Nitrogen – Appropriate Method
Between 2003-06 and 2011, the following trends related to
nitrogen application method were noted in the Chesapeake
Bay region’s cultivated cropland (table 2.7):
 Nitrogen receiving acres on which nitrogen application
method criteria were met for all crops in rotation: 7
percentage point decline, decreased from 34 to 27
percent of cropped acres;
 Nitrogen receiving acres on which nitrogen application
method criteria were met for some but not all crops in
rotation: 10 percentage point improvement, increased
from 45 to 55 percent of cropped acres; and
 Nitrogen receiving acres on which nitrogen application
method criteria were not met on any crop in the
rotation: maintained 2003-06 conservation levels (21
and 18 percent of cropped acres in 2003-06 and 2011,
respectively).

Between 2003-06 and 2011, the following trends related to
nitrogen application method were noted in the Chesapeake
Bay region’s cultivated cropland acres receiving commercial
fertilizer as their sole nitrogen source, with no manure inputs
(table 2.7):
 Commercial nitrogen receiving acres (no manure
inputs) on which nitrogen application method criteria
were met on all crops in rotation: maintained 2003-06
conservation levels (41 to 37 percent of cropped acres
in 2003-06 and 2011, respectively);
 Commercial nitrogen receiving acres (no manure
inputs) on which nitrogen application method criteria
were met on some but not all crops in rotation: 10
percentage point improvement, increased from 34 to 44
percent; and
 Commercial nitrogen receiving acres (no manure
inputs) on which nitrogen application method criteria
were not met on any crop in the rotation: 6 percentage
point improvement, increased from 25 to 19 percent of
cropped acres.
Between 2003-06 and 2011, the following trends related to
nitrogen application method were noted in the Chesapeake
Bay region’s cultivated cropland acres receiving manure
inputs as a nitrogen source, with or without additional
commercial fertilizer inputs (table 2.7):
 Manured acres on which nitrogen application method
criteria were met on all crops in rotation: 6 percentage
point decline, decreased from 22 to 16 percent;
 Manured acres on which nitrogen application method
criteria were met on some but not all crops in rotation:
maintained 2003-06 conservation levels (63 and 67
percent of cropped acres in 2003-06 and 2011,
respectively); and
 Manured acres on which nitrogen application timing
criteria were not met on any crop in the rotation:
maintained 2003-06 conservation levels (16 and 17
percent of cropped acres in 2003-06 and 2011,
respectively).
Management of nitrogen application method on acres
receiving manure was very similar in both survey periods,
with approximately 84 percent of manured acres managed
with incorporation at some point in the rotation. The increase
in manured acres and the presumed concurrent increase in
manure users may partially explain the decline in acres
utilizing proper manure application techniques on all crops in
rotation. The increase in acres under no-till could also explain
this decline in use of appropriate application method.
Appropriate manure application includes incorporation into
the soil, which is not easily accommodated by no-till systems.
Application techniques of knifing or injecting manures could
be employed to maintain a low disturbance tillage system, but
the manure form would need to be amenable to these
technologies. In management systems with manure
applications, a mulch-till system may be more appropriate
than a no-till system, as mulch-till systems allow light disking
of the manure at application.

29

Table 2.7. Nitrogen management practices and percent of cropped acres within each category for the Chesapeake Bay region, 2003-06
and 2011.
Nitrogen*
2003-06
2011
2003-06
2011
No N applied to any crop in rotation

acres
214,000

acres
87,000

percent
5

percent
2

2,457,000
1,608,000

2,177,000
2,089,000

95
60
40

98
51
49

32
54
13

23
71
6

42
52
6

35
62
3

17
59
24

9
82
9

50
34
11

36
50
11

69
15
9

59
25
13

18
66
16

12
78
10

34
45
21

27
55
18

41
34
25

37
44
19

22
63
16

16
67
17

13

7

87

93

For acres where N is applied:
Commercial Fertilizer Only
Manure with or without Commercial Fertilizer

Rate of application:
Acres receiving commercial fertilizer and/or manure applications:
All crops in rotation meet the nitrogen rate criteria described in text
Some but not all crops in rotation meet the nitrogen rate criteria described in text
No crops in rotation meet the nitrogen rate criteria described in text
Acres receiving commercial fertilizer applications only:
All crops in rotation meet the nitrogen rate criteria described in text
Some but not all crops in rotation meet the nitrogen rate criteria described in text
No crops in rotation meet the nitrogen rate criteria described in text
Acres receiving manure with or without commercial fertilizer applications:
All crops in rotation meet the nitrogen rate criteria described in text
Some but not all crops in rotation meet the nitrogen rate criteria described in text
No crops in rotation meet the nitrogen rate criteria described in text
Time of application:
Acres receiving commercial fertilizer and/or manure applications:
All crops in rotation have application of nitrogen fertilizer less than 21 days before planting
Some but not all crops have application of nitrogen fertilizer within 21 days before planting
No crops in rotation have application of nitrogen fertilizer within 21 days before planting
Acres receiving commercial fertilizer applications only:
All crops in rotation have application of nitrogen fertilizer less than 21 days before planting
Some but not all crops have application of nitrogen fertilizer within 21 days before planting
No crops in rotation have application of nitrogen fertilizer within 21 days before planting
Acres receiving manure with or without commercial fertilizer applications:
All crops in rotation have application of manure less than 21 days before planting
Some but not all crops have application of manure within 21 days before planting
No crops in rotation have application of manure within 21 days before planting
Method of application:
Acres receiving commercial fertilizer and/or manure applications:
All crops in rotation have N applied with incorporation or banding/foliar/spot treatment
Some but not all crops in rotation have N applied with incorporation or banding/foliar/spot treatment
No crops in rotation have N applied with incorporation or banding/foliar/spot treatment
Acres receiving commercial fertilizer applications only:
All crops in rotation have N applied with incorporation or banding/foliar/spot treatment
Some but not all crops in rotation have N applied with incorporation or banding/foliar/spot treatment
No crops in rotation have N applied with incorporation or banding/foliar/spot treatment
Acres receiving manure with or without commercial fertilizer applications:
All crops in rotation have manure applied with incorporation or banding/foliar/spot treatment
Some but not all crops in rotation have manure applied with incorporation or banding/foliar/spot treatment
No crops in rotation have manure applied with incorporation or banding/foliar/spot treatment
Rate and timing and method of application (excludes acres not receiving nitrogen)
All crops meet the nitrogen rate criteria described in text and application within 3 weeks before planting with
incorporation or banding/foliar/spot treatment
Some but not all crops meet the nitrogen rate criteria described in text or application within 3 weeks before
planting with incorporation or banding/foliar/spot treatment

Nitrogen and Phosphorus
Crop rotation phosphorus and nitrogen rates meet criteria described in text and all applications occur within 3 weeks
before planting and include incorporation or banding/foliar/spot treatment, including acres with no nitrogen or
phosphorus applied
8
5
Note: Percents may not add to 100 because of rounding.
* These estimates include adjustments made to the reported data on nitrogen and phosphorus application rates from the survey because of missing data and data entry
errors. In the case of phosphorus, the 3-year data period for which information was reported was too short to pick up phosphorus applications made at 4- and 5-year
intervals between applications, which is a common practice for producers adhering to sound phosphorus management techniques. Since crop growth, and thus canopy
development which decreases erosion, is a function of nitrogen and phosphorus, it was necessary to add additional nitrogen when the reported levels were insufficient to
support reasonable crop yields throughout the 52 years in the model simulation. For additional information on adjustment of nutrient application rates, see “Adjustment
of CEAP Cropland Survey Nutrient Application Rates for APEX Modeling,” available at http://www.nrcs.usda.gov/technical/nri/ceap).

30

Figure 2.3. Average annual percent of cropped acres in each of the subareas receiving manure in the Chesapeake Bay region, 2003-06
and 2011.

Percent of cropped acres

70
60
50
40
30
20
10
0
0205

0206

0207

0208

Chesapeake Bay
region

2003-06

53

34

43

1

38

2011

61

39

49

16

48

*0205=Susquehanna River Basin; 0206=Upper Chesapeake Bay; 0207=Potomac River Basin; 0208=Lower Chesapeake Bay.

Phosphorus – Appropriate Rate
Phosphorus is often applied infrequently, with the intent of an
application providing phosphorus availability for multiple crops
or years. Therefore, although nitrogen rate criteria can be applied
to each crop in the rotation, phosphorus application rate criteria
apply only to the full crop rotation. The appropriate rate is
determined by the sum of all applications over the entire rotation
divided by the sum of all crop removal at harvest and should
equal 1.2 or less (see discussion at the end of the “Appropriate
Rate Criteria” section above). Between 2003-06 and 2011, the
following trends related to phosphorus application rates were
noted in the Chesapeake Bay region’s cultivated cropland (table
2.8):
 Phosphorus receiving acres on which phosphorus
application rate criteria were met: maintained 2003-06
conservation levels (54 and 57 percent of cropped acres in
2003-06 and 2011, respectively);
 Phosphorus receiving acres on which phosphorus
application rate criteria were not met: maintained 2003-06
conservation levels (46 and 43 percent of cropped acres in
2003-06 and 2011, respectively); and
 Cropped acres with no phosphorus application: maintained
2003-06 conservation levels (1 and <1 percent of cropped
acres in 2003-06 and 2011, respectively).
Commercial fertilizer was the only source of phosphorus for 2.4
and 2.3 million cropped acres in 2003-06 and 2011, respectively.
Between 2003-06 and 2011, the following trends related to
phosphorus application rates were noted in the Chesapeake Bay
region’s cultivated cropland acres receiving commercial fertilizer
as their sole phosphorus source, with no manure inputs (table 2.8):
 Commercial phosphorus receiving acres (no manure
inputs) on which phosphorus application rate criteria were
met: 8 percentage point improvement, increased from 68 to
76 percent; and

 Commercial phosphorus receiving acres (no manure
inputs) on which phosphorus application rate criteria were
not met: 8 percentage point improvement, decreased from
32 to 24 percent.
Even though acreage receiving manure inputs as a phosphorus
fertilizer source increased from 1.6 to 2.1 million acres, the trends
previously noted related to nitrogen application rates and manure
adoption were not apparent in the relationship between
phosphorus application rates and manure adoption. Between
2003-06 and 2011, the practice of applying manures as a
phosphorus source increased from occurring on 40 to 48 percent
of phosphorus receiving cropped acres in the region, but there
were neither improvements nor declines in phosphorus rate
application adherence associated with the adoption of manure as a
phosphorus source. Between 2003-06 and 2011, the following
trends related to phosphorus application rates were noted in the
Chesapeake Bay region’s cultivated cropland acres receiving
manure inputs as a phosphorus source, with or without additional
commercial fertilizer inputs (table 2.8):
 Manured acres on which phosphorus application rate
criteria were met: maintained 2003-06 conservation levels
(32 and 35 percent of cropped acres in 2003-06 and 2011,
respectively); and
 Manured acres on which phosphorus application rate
criteria were not met: maintained 2003-06 conservation
levels (68 and 65 percent of cropped acres in 2003-06 and
2011, respectively).
In 2003-06 and 2011, 20 and 25 percent of manured cropped acres
had nutrient application rates at or below crop removal rates. The
continued adherence to this management may indicate an
improvement in manure management and adherence to soil test
results and/or manure test results for the possibility of reducing
soil phosphorus stores.

31

Phosphorus – Appropriate Timing
Between 2003-06 and 2011, the following trends related to
phosphorus application timing were noted in the Chesapeake Bay
region’s cultivated cropland (table 2.8):
 Cropped acres on which phosphorus application timing
criteria were met for all crops in rotation: 11 percentage
point decline, decreased from 53 to 42 percent;
 Cropped acres on which phosphorus application timing
criteria were met for some but not all crops in rotation:
maintained 2003-06 conservation levels (34 and 38 percent
of cropped acres in 2003-06 and 2011, respectively); and
 Cropped acres on which phosphorus application timing
criteria were not met on any crop in the rotation: 6
percentage point decline, decreased from13 and 19
percent.
Between 2003-06 and 2011, the following trends related to
phosphorus application timing were noted in the Chesapeake Bay
region’s cultivated cropland acres receiving commercial fertilizer
as their sole phosphorus source, with no manure inputs (table 2.8):
 Commercial phosphorus receiving acres (no manure
inputs) on which phosphorus application timing criteria
were met on all crops in rotation: 6 percentage point
decline, decreased from 75 to 69 percent;
 Commercial phosphorus receiving acres (no manure
inputs) on which phosphorus application timing criteria
were met on some but not all crops in rotation: maintained
2003-06 conservation levels (13 and 18 percent of cropped
acres in 2003-06 and 2011, respectively); and
 Commercial phosphorus receiving acres (no manure
inputs) on which phosphorus application timing criteria
were not met on any crop in the rotation: maintained
2003-06 conservation levels (12 and 11 percent of cropped
acres in 2003-06 and 2011, respectively).
Between 2003-06 and 2011, the following trends related to
phosphorus application timing were noted in the Chesapeake Bay
region’s cultivated cropland acres receiving manure inputs as a
phosphorus source, with or without additional commercial
fertilizer inputs (table 2.8):
 Manured acres on which phosphorus application timing
criteria were met on all crops in rotation: maintained 200306 conservation levels (16 and 13 percent of cropped acres
in 2003-06 and 2011, respectively);
 Manured acres on which phosphorus application timing
criteria were met on some but not all crops in rotation: 8
percentage point decline, decreased from 67 to 59 percent;
and
 Manured acres on which nitrogen application timing
criteria were not met on any crop in the rotation: 12
percentage point decline, increased from 16 to 28 percent.
These results suggest that there is significant opportunity to
improve the timing of manure applications, particularly when the
manures are being used as a phosphorus source.

Phosphorus – Appropriate Method
Overall, the surveys revealed that there was no significant change
in adoption of more or less responsible phosphorus application

methods. Between 2003-06 and 2011, the following trends related
to phosphorus application methods were noted in the Chesapeake
Bay region’s cultivated cropland (table 2.8):
 Phosphorus receiving acres on which phosphorus
application method criteria were met for all crops in
rotation: maintained 2003-06 conservation levels (42 and
37 percent of cropped acres in 2003-06 and 2011,
respectively);
 Phosphorus receiving acres on which phosphorus
application method criteria were met for some but not all
crops in rotation: maintained 2003-06 conservation levels
(28 and 30 percent of cropped acres in 2003-06 and 2011,
respectively); and
 Phosphorus receiving acres on which phosphorus
application method criteria were not met on any crop in
the rotation: maintained 2003-06 conservation levels (30
and 32 percent of cropped acres in 2003-06 and 2011,
respectively).
Phosphorus application method management in systems with only
commercial phosphorus sources and no inclusion of manures
improved slightly between 2003-06 and 2011. Between 2003-06
and 2011, the following trends related to phosphorus application
method were noted in the Chesapeake Bay region’s cultivated
cropland acres receiving commercial fertilizer as their sole
phosphorus source, with no manure inputs (table 2.8):
 Commercial phosphorus receiving acres (no manure
inputs) on which phosphorus application method criteria
were met on all crops in rotation: maintained 2003-06
conservation levels (51 and 53 percent of cropped acres in
2003-06 and 2011, respectively);
 Commercial phosphorus receiving acres (no manure
inputs) on which phosphorus application method criteria
were met on some but not all crops in rotation: 7
percentage point improvement, increased from 19 to 26
percent; and
 Commercial phosphorus receiving acres (no manure
inputs) on which phosphorus application method criteria
were not met on any crop in the rotation: 9 percentage
point improvement, declined from 31 to 22 percent.
Phosphorus application method management in manured systems
did not improve between 2003-06 and 2011. Between 2003-06
and 2011, the following trends related to phosphorus application
methods were noted in the Chesapeake Bay region’s cultivated
cropland acres receiving manure inputs as a phosphorus source,
with or without additional commercial fertilizer inputs (table 2.8):
 Manured acres on which phosphorus application method
criteria were met on all crops in rotation: 7 percentage
point decline, decreased from 28 to 21 percent;
 Manured acres on which phosphorus application method
criteria were met on some but not all crops in rotation: 7
percentage point decline, decreased from 42 to 35 percent;
and
 Manured acres on which nitrogen application timing
criteria were not met on any crop in the rotation: 14
percentage point decline, increased from 30 to 44 percent.
These results indicate a significant need for improving manure
application methods.

32

Table 2.8. Phosphorus management practices and percent cropped acres within each category for the Chesapeake Bay region, 2003-06
and 2011.
Phosphorus*
2003-06
2011
2003-06
2011
No P applied to any crop in rotation

acres
43,000

acres
<1

2,414,000
1,608,000

2,264,000
2,089,000

For acres where P is applied:
Commercial Fertilizer Only
Manure with or without Commercial Fertilizer

Rate of application:
Acres receiving commercial fertilizer and/or manure applications:
Rotation meets the phosphorus rate criteria described in text
Some but not all crops in the rotation meet the phosphorus rate criteria described in text
Acres receiving commercial fertilizer applications only:
Rotation meets the phosphorus rate criteria described in text
Some but not all crops in the rotation meet the phosphorus rate criteria described in text
Acres receiving manure with or without commercial fertilizer applications:
All crops in rotation meet the phosphorus rate criteria described in text
Some but not all crops in the rotation meet the phosphorus rate criteria described in text
Time of application:
Acres receiving commercial fertilizer and/or manure applications:
All applications of phosphorus fertilizer less than 21 days before planting
Some but not all applications of phosphorus fertilizer within 21 days before planting
No applications of phosphorus fertilizer within 21 days before planting
Acres receiving commercial fertilizer applications only:
All applications of phosphorus fertilizer less than 21 days before planting
Some but not all applications of phosphorus fertilizer within 21 days before planting
No applications of phosphorus fertilizer within 21 days before planting
Acres receiving manure with or without commercial fertilizer applications:
All applications of phosphorus fertilizer less than 21 days before planting
Some but not all applications of phosphorus fertilizer within 21 days before planting
No applications of phosphorus fertilizer within 21 days before planting
Method of application:
Acres receiving commercial fertilizer and/or manure applications:
All applications of phosphorus include incorporation or banding/foliar/spot treatment
Some but not all applications of phosphorus include incorporation or banding/foliar/spot treatment
No applications of phosphorus include incorporation or banding/foliar/spot treatment
Acres receiving commercial fertilizer applications only:
All applications of phosphorus include incorporation or banding/foliar/spot treatment
Some but not all applications of phosphorus include incorporation or banding/foliar/spot treatment
No applications of phosphorus include incorporation or banding/foliar/spot treatment
Acres receiving manure with or without commercial fertilizer applications:
All applications of phosphorus include incorporation or banding/foliar/spot treatment
Some but not all applications of phosphorus include incorporation or banding/foliar/spot treatment
No applications of phosphorus include incorporation or banding/foliar/spot treatment
Rate and timing and method of application (excludes acres not receiving phosphorus):
All applications meet the phosphorus rate criteria described in text and application within 3 weeks before planting
with incorporation or banding/foliar/spot treatment
Some but not all applications meet the phosphorus rate criteria described in text or application within 3 weeks
before planting with incorporation or banding/foliar/spot treatment

percent
1

percent
<1

99
60
40

100
52
48

54
46

57
43

68
32

76
24

32
68

35
65

53
34
13

42
38
19

75
13
12

69
18
11

16
67
16

13
59
28

42
28
30

37
30
32

51
19
31

53
26
22

28
42
30

21
35
44

22

21

78

79

Nitrogen and Phosphorus
Crop rotation phosphorus and nitrogen rates meet criteria described in text and all applications occur within 3 weeks
before planting and include incorporation or banding/foliar/spot treatment, including acres with no nitrogen or
phosphorus applied
8
5
Note: Percents may not add to 100 because of rounding.
* These estimates include adjustments made to the reported data on nitrogen and phosphorus application rates from the survey because of missing data and data entry
errors. In the case of phosphorus, the 3-year data period for which information was reported was too short to pick up phosphorus applications made at 4- and 5-year
intervals between applications, which is a common practice for producers adhering to sound phosphorus management techniques. Since crop growth, and thus canopy
development which decreases erosion, is a function of nitrogen and phosphorus, it was necessary to add additional phosphorus when the reported levels were
insufficient to support reasonable crop yields throughout the 52 years in the model simulation. (For additional information on adjustment of nutrient application rates,
see “Adjustment of CEAP Cropland Survey Nutrient Application Rates for APEX Modeling,” available at http://www.nrcs.usda.gov/technical/nri/ceap).

33

Nitrogen and Phosphorus Management – Rate,
Timing, and Method
The avoidance component of the ACT strategy is partially
achieved through appropriate nutrient application
management, including the 4Rs (right rate, right timing, right
method, and right form of application). Nutrient application
management planning and actuation did not see the significant
gains accomplished in the adoption of Control and Trap
practices. However, there was a generally positive trend in the
observed decline of acreage on which no crops in rotation had
appropriate rate, timing, or method of nutrient application.
There was also a trend towards a slight decline in acres on
which all crops in rotation received appropriate rate, timing, or
method of nutrient application. While most acres have
evidence of some nitrogen or phosphorus management, the
majority of the acres in the region lack consistent use of the
4Rs on each crop in every year of production. This is
especially true for manured acres, on which the 4Rs are not
being met through comprehensive nutrient management plans.
Between 2003-06 and 2011, the following trends related to
achieving right rate, right timing, and right method of nutrient
application were noted in the Chesapeake Bay region’s
cultivated cropland acres (tables 2.7 and 2.8):
 Nitrogen receiving acres on which all crops were
managed with the right nitrogen rate, timing, and
method: 6 percentage point decline, decreased from 13
to 7 percent;
 Nitrogen receiving acres on which some but not all of
the 4Rs were met for nitrogen application management:
6 percentage point improvement, increased from 87 to
93 percent;
 Phosphorus receiving acres on which all crops were
managed with the right phosphorus rate, timing, and
method: maintained 2003-06 conservation levels (22
and 21 percent of cropped acres in 2003-06 and 2011,
respectively);
 Phosphorus receiving acres on which some but not all
of the 4Rs were met for phosphorus application
management: maintained 2003-06 conservation levels
(78 and 79 percent of cropped acres in 2003-06 and
2011, respectively); and
 Nutrient receiving acres on which all crops were
managed with the right rate, timing, and method for
both nitrogen and phosphorus: maintained 2003-06
conservation levels (8 and 5 percent of cropped acres in
2003-06 and 2011, respectively).
A number of factors may contribute to current challenges in
nutrient application management. First, cropped acres
receiving manure increased from 38 to 48 percent between
2003-06 and 2011 (fig. 2.3). The negative trends in timing and
method of manure application may be the result of traditional
manure users applying manure to more acres. The greater time
requirement associated with spreading manure on more acres
may inhibit their ability to meet application timing criteria.
Also, new manure users may be adjusting to managing this
new nutrient source. Further complicating the issue of
responsible manure management is the widespread adoption of
conservation tillage systems. No-till systems in particular
require changes in form and/or method of manure application

in order to maintain a no-till system while also meeting
responsible manure application criteria. A number of
technologies and methodologies have been developed to
reduce soil disturbance associated with manure incorporation.
For example, a no-till system is compatible with injected
liquid manures. Alternatively, light disking associated with
mulch-till systems would allow the farmer to maintain a
conservation tillage system while also meeting the
incorporation needs of manures. This approach would keep
soil disturbance at a minimum while still incorporating
manure, thus reducing the risk of nutrient loss. A final factor
potentially complicating nutrient management in the region is
the widespread adoption of new cropping systems (tables 2.3,
2.5, and 2.6).

Nutrient Application Management
Treatment Levels
Four treatment levels indicating management intensity for
nitrogen and phosphorus were derived to enable evaluation of
nutrient management levels in the Chesapeake Bay region
during both survey periods. Management treatment levels
were combined with soil risk classes to construct conservation
treatment levels, which estimate under-treated acres and
treatment needs in chapter 4. Criteria for the scoring system
for determining treatment levels are presented in Appendix D.
The same scoring classification was used in classifying the
level of nutrient application management in place during each
survey period. This scoring and evaluation system differs from
the previous report’s evaluation process and therefore the
classification of acres will not be directly comparable between
this and the original Chesapeake Bay region CEAP report
(USDA NRCS 2011). This new classification system applies a
score for rate, timing, and method. The classification method
accommodates manure and commercial fertilizer management
and allows for split applications. Although it is not discussed
in this report, the appropriateness of the form of nutrient being
delivered should be considered in conjunction with rate,
method, and timing of nutrient application in the development
of sound nutrient management plans. The choice of form is
often dictated by the farm operation and economics. The
maximum score is 60 points, with 20 potential points in each
category (rate, timing, and method) (Appendix D). Treatment
level scores are as follows:
 High: 45 or more points; represents acres with nutrient
management meeting or exceeding management
criteria in each of the three scoring categories;
 Moderately High: Less than 45 points but more than
or equal to 30 points; requires that management in at
least 1 category meets or exceeds acceptable criteria;
 Moderate: Less than 30 points but more than or equal
to 20 points; generally requires rate, timing, or method
management score to be at or near appropriate levels;
and
 Low: Less than 20 points; management in no category
meets the criteria to qualify as appropriate application
management.

34

In reference to nitrogen fertilizer applications, the percent of
cropped acres with high (5 and 6 percent of cropped acres in
2003-06 and 2011, respectively) and low (21 and 20 percent of
cropped acres during 2003-06 and 2011, respectively) levels
of conservation practices for nitrogen application management
were maintained at 2003-06 levels during both survey periods
(fig. 2.4). Acreage receiving moderately high nitrogen
application management declined by 11 percent, decreasing
from 39 to 28 percent of cropped acres between 2003-06 and
2011. Concurrently, acreage receiving moderate levels of
treatment increased from 34 to 47 percent of cropped acres
between 2003-06 and 2011 (fig. 2.4).
As noted in table 2.7, relative to 2003-06, nitrogen application
management in 2011 was less consistent in application of
appropriate rates, timing, and method for all crops in rotation on
a given acre. The increase in acres with manure application
providing nitrogen inputs between 2003-06 and 2011 appears to
be a driver of this decline. Non-manured acres with moderately
high treatment levels declined from 33 to 22 percent of acres
between 2003-06 and 2011. This 11 percentage point decline
occurred at the same time manured acres with moderate
treatment levels of nitrogen application management
experienced an 11 percentage point increase (fig. 2.4)
Between 2003-06 and 2011, acres receiving low levels of
nitrogen application management remained constant, whether
manured (16 and 15 percent of cropped acres in 2003-06 and
2011, respectively) or non-manured (5 percent in both survey
periods). Similarly, acres receiving high levels of nitrogen
application management remained constant, whether manured
(<1 and 1 percent of cropped acres in 2003-06 and 2011,
respectively) or non-manured (5 percent in both survey
periods).
Phosphorus application management did not change appreciably
between the two survey periods (fig. 2.5). Overall, the percent
of cropped acres were high (24 and 27 percent of cropped acres
in 2003-06 and 2011, respectively), moderate (19 and 18
percent of cropped acres in 2003-06 and 2011, respectively),
and low (19 and 22 percent of cropped acres in 2003-06 and
2011, respectively). Levels of conservation practices for
phosphorus application management were maintained at 200306 levels during both survey periods (fig. 2.3). Acreage
receiving moderately high phosphorus application management
declined by 6 percent, decreasing from 38 to 32 percent of
cropped acres between 2003-06 and 2011. The only change
noted in non-manured acreage phosphorus application
management occurred in the moderately high treatment
category, where acreage declined 7 percentage points, from 28
to 21 percent of all cropped acres. Phosphorus application
management of manured acres did not change between the two
survey periods (fig. 2.5). The ability to maintain 2003-06
conservation levels could be considered a positive outcome,
considering the 10 percent increase in manured acres that
occurred between the two survey periods (fig. 2.3).

Manure Management
The 2011 data in the Chesapeake Bay CEAP analysis indicate
both increased manure application in the Chesapeake Bay

region and a complementary increased awareness of nutrient
management concerns associated with manure application.
However, as noted in the previous sections on nutrient
management trends, opportunity remains to improve adoption
of consistent and proper nutrient application management
plans.
In 2011, the percent of acres on which manure was used as a
nutrient source increased or were maintained at 2003-06 levels
in each of the four subregions of the Chesapeake Bay region
(fig. 2.3). The basin with the highest percentage of acres
receiving manure applications is the Susquehanna River Basin
(subregion 0205), in which manure use increased from
occurring on 53 to 61 percent of cropped acres between 200306 and 2011 (fig. 2.3). The largest change in manure adoption
was seen in the Lower Chesapeake Bay subregion (0208),
where manured acreage increased from 1 to 16 percent of
cropped acres between 2003-06 and 2011. Still, the Lower
Chesapeake Bay subregion remains the subregion with the
fewest manured acres and the lowest percent of cropped acres
receiving manure.
In 2003-06, 13.4 million tons of manure was applied in one or
more years of the crop rotation to 38 percent of the cropped
acres in the Chesapeake Bay region (1.6 million acres) (fig.
2.3). By 2011, the amount of manure applied had increased to
22.1 million tons and the acreage receiving manure had
increased to 48 percent of the cropped acres in the Chesapeake
Bay region (2.1 million acres). This change is calculated on a
weight basis rather than on the basis of the nutrient content of
the applied manure.
The 65 percent increase in total tons of manure applied
between 2003-06 and 2011 occurred with a trend toward fluid
manure applications. Manure in liquid form accounted for 26
percent of total manure applied in 2003-06 and 42 percent of
the total in 2011.
Manure application rates also increased between 2003-06 and
2011, rising from an average application rate of 12.6 to 16.8
tons per acre per year, respectively. The average per acre
amount of nitrogen applied as manure increased by 13 percent,
rising from 22.0 to 24.8 pounds per acre between 2003-06 and
2011. The average per acre application of phosphorus applied
as manure increased by 10 percent, rising from 3.7 to 4.1
pounds per acre between 2003-06 and 2011.
Manure from livestock producers is being spread on more
acres and in particular, on off-farm acres. In this context, offfarm acres are those cropped acres on farms where manure is
not produced. While acreage receiving manure increased by
half a million acres, acreage receiving manure produced onfarm actually decreased slightly, falling from 883,000 acres in
2003-06 to 865,000 acres in 2011. The cropped acres
receiving manure from on-farm sources represented 83 percent
of the total manured acres in 2003-06, but only 66 percent in
2011. The number of manured acres on which the operator
purchased manure nearly quadrupled between 2003-06 and
2011, rising from 57,000 acres to 203,000 acres (fig. 2.6).

35

Figure 2.4. Conservation treatment levels for nitrogen application management level in the Chesapeake Bay region, 2003-06 and
2011.
Percent of Cropped Acres

35
30
25
20
15
10
5
0

Low

Moderate

Mod-High

High

2003-06 Manured

16

15

6

0

2011 Manured

15

26

6

1

2003-06 No Manure

5

19

33

5

2011 No Manure

5

21

22

5

*See Appendix D for explanation of criteria delineating the four levels of nitrogen management intensity, Low, Moderate, Moderately High (Mod-High), and High.

Figure 2.5. Conservation treatment levels for phosphorus application management level in the Chesapeake Bay region, 2003-06 and
2011.

Percent of Cropped Acres

30
25
20
15
10
5
0

Low

Moderate

Mod-High

High

2003-06 Manured

16

9

10

3

2011 Manured

20

13

11

3

2003-06 No Manure

3

10

28

21

2011 No Manure

2

5

21

24

*See Appendix D for explanation of criteria delineating the four levels of phosphorus management intensity, Low, Moderate, Moderately High (Mod-High), and High.

36

Additionally, the region saw a doubling of manured acres on
which the operator was paid to apply manure; these rose from
24,000 to 55,000 acres between 2003-06 and 2011 (fig. 2.6).
The proportion of manured acres where tested manures were
applied increased from 15 percent (154,000 acres) in 2003-06
to 37 percent (488,000 acres) in 2011. There have been
vigorous education campaigns in the past decade in the
Chesapeake Bay region to encourage operators to do better
phosphorus management, which would at least in part account
for lower phosphorus application rates per acre in 2011 with
tested manure.
In the Chesapeake Bay region, the percent of acres being
applied with manure according to a requirement or standard
increased from 14 to 42 percent between 2003-06 and 2011.
Of the 14 percent of manured acres receiving manure
according to a requirement or standard in 2003-06, 36 percent
had manure applied at a nitrogen standard and 14 percent had

manure applied at a phosphorus standard. In 2011, only 16
percent of manured acres had manure applied at a nitrogen
standard, but 24 percent applied manure at a phosphorus
standard. Both the increase in acres receiving manure
according to a requirement or standard in 2011, and the
increase of acres applying manure according to a phosphorus
analysis during the same period signal a concerted effort to
address nutrient management concerns in the Chesapeake Bay
(fig. 2.5).
In the 2011 survey, operators were asked for the soil test
phosphorus level in the field if the manure was applied
according to a requirement or standard. Responses indicate
that 25 percent of acres receiving manure in 2011 according to
a requirement or standard had a soil test to determine the
phosphorus level before manure was applied. However, this
question was not included in the 2003-06 survey, so no trend
could be noted.

Figure 2.6. Cropland acres where manure was purchased or where the operator was paid to apply manure in the Chesapeake Bay
region, 2003-06 and 2011.
250,000

Acres

200,000
150,000
100,000
50,000
0

Purchased Manure was Applied

Operator was Paid to Apply Manure

2003-06 acres

57,000

24,000

2011 acres

203,000

55,000

37

Chapter 3
Onsite (Field-Level) Effects of
Conservation Practices
Relative to the original Chesapeake Bay region CEAP report
(USDA NRCS 2011), this report applies an updated version of
the APEX model, revised soils data, a different soil erosion
equation, new weather data, and improved methods of
accounting for conservation practices. To enable comparisons
between the 2003-06 baseline conditions and the 2011
conservation conditions, the 2003-06 data and the 2011 data
were each analyzed with the same constraints under the
improved modeling system. Because of these changes, the
data analyses for 2003-06 data produced different values than
those reported in the original Chesapeake Bay region CEAP
report (USDA NRCS 2011).
The use of cover crops was the most significant change in
conservation practice adoption in the region, increasing from
use on only 12 to 52 percent of cultivated cropland acres in
2003-06 and 2011, respectively. Cover crops are a unique
conservation practice in that they impact both surface and
subsurface loss pathways by reducing runoff and scavenging
excess nutrients from previous crops. However, cover crops,
like any singular conservation practice, are not a panacea. The
efficacy of cover crops for reducing subsurface losses is
highly dependent upon their frequency of use, other
conservation and management practices applied, and the
hydrologic properties of the soil in which they are grown.
Unless they are paired with a responsible nutrient application
plan, cover crops are less effective in the near term on soils
with an inherently high leaching potential because these soils
quickly lose applied nutrients to the environment when they
are not utilized by the primary crop or are lost before the cover
is planted. Coarse textured soils with high leaching potentials
are especially benefited by consistent cover crop use and
reduced tillage, two complementary management techniques
that improve the soils’ ability to retain water and nutrients.
Because of the importance of cover crop use in this region a
model scenario was developed to assess the effects of cover
crop application frequency on the overall benefits of the
practice. Specifically the scenario considered the added
benefit cover crops provide related to reduction of sediment
and nutrient losses, as well as the improvements in soil
organic carbon. The simulated losses under the 2011
conservation condition were compared to a scenario in which
all 2011 conservation practices were maintained with the
exception of cover crop application. This assumes that farmers
surveyed in 2011 did not alter any other crop field operations
or plant dates in the absence of cover crops. The estimated
increased benefit is an average across a variety of soil types
and suites of conservation systems employed with the cover
crops. The improvement attributable to cover crops regarding
the reduction of sediment, nitrogen, and phosphorus losses, as
well as the changes in soil carbon dynamics are discussed in
each loss pathway’s section.

The Field-Level Cropland Model—APEX
A physical process-based model, the Agricultural Policy
Environmental eXtender (APEX), was used to simulate longterm effects of conservation practice adoption at the field scale
(Williams et al. 2006; Williams et al. 2008; Gassman et al.
2009 and 2010).7 The I_APEX model run management
software, developed at the Center for Agricultural and Rural
Development (Iowa State University), was used to perform the
simulations in batch mode.8
The APEX model is a field-scale, daily time-step model able
to simulate interactions between weather, farming operations,
crop growth and yield, and the movement of water, soil,
carbon, nutrients, sediment, and pesticides (fig. 3.1). APEX
and its predecessor, EPIC (Environmental Policy Impact
Calculator), have a long history of use in simulation of
agricultural and environmental processes and the effect of
agricultural technology and government policy on natural
resources (Izaurralde et al. 2006; Williams 1990; Williams et
al. 1984; Gassman et al. 2009).9
APEX simulates the effects of farming operations such as
planting; tillage; application of commercial fertilizers,
manures, and pesticides; irrigation; and harvest operations.
Daily weather events and their interaction with crop cover and
soil properties are simulated on a daily basis to realistically
affect simulated crop growth and the fate and transport of
water and chemicals through the soil profile and over land to
the edge of the field. The model transforms crop residue
remaining on the field after harvest into organic matter, which
the model may degrade quickly or allow to build up in the soil
over time, depending on the residue quality, tillage system,
and site-specific conditions.
APEX also simulates all of the basic biological, chemical,
hydrological, and meteorological processes of farming
systems and their interactions on a daily time-step. Simulated
soil erosion includes wind erosion, sheet and rill erosion, and
the loss of sediment beyond the edge of the field. The
nitrogen, phosphorus, and carbon cycles are simulated,
including chemical transformations in the soil that affect
nutrient availability for plant growth or for transport from the
field. Gaseous exchange between the soil and the atmosphere
is simulated, including losses of gaseous nitrogen.

7

The full theoretical and technical documentation of APEX can be found at
http://epicapex.brc.tamus.edu/downloads/user-manuals.aspx.
8

The I_APEX software steps through the simulations one at a time, extracting
the needed data from the Access input tables, executes APEX, and then stores
the model output in Access output files. The Web site for that software is
http://www.card.iastate.edu/environment/interactive_programs.aspx.
9

Summaries of APEX model validation studies on how well APEX simulates
measured data are presented in Gassman et al. (2009) and in “APEX Model
Validation for CEAP” found at http://www.nrcs.usda.gov/technical/nri/ceap.

38

Figure 3.1. Daily hydrologic processes simulated by APEX.

Effects of Practices on Fate and Transport
of Water
The hydrologic conditions of cropped acres in the Chesapeake
Bay region interact with or drive the estimates of sediment and
nutrient losses from these agroecological systems. The APEX
model simulates hydrologic processes at the field scale,
accounting for precipitation, irrigation, evapotranspiration,
surface water runoff, infiltration, and percolation beyond the
bottom of the soil profile.
Precipitation, sometimes supplemented by irrigation, supplies
water to cropped acres. Annual precipitation used in the 52year simulation averaged about 42 inches across the
Chesapeake Bay region (table 3.1). Annual precipitation
ranged from 34 to 46 inches per year, with some points
experiencing up to 68 inches in wet years and other points
experiencing as little as 26 inches during dry years.
Approximately 5 and 6 percent of cropped acres were irrigated
in 2003-06 and 2011, respectively. Between 2003-06 and
2011, the estimated per acre irrigation rate decreased by 7
percent, dropping from an average of 7.5 to 7.0 inches of
irrigation water applied per acre per year (table 3.1).
Evapotranspiration, a combination of evaporation and
transpiration by which water is lost to the atmosphere, remains
the dominant water loss pathway for cropped acres in the
Chesapeake Bay region (table 3.1). Evapotranspiration
accounted for 57 and 58 percent of water losses from
cropped acres in 2003-06 and 2011, respectively. On average,
transpiration losses totaled 24.2 and 24.9 inches of water per
acre per year in 2003-06 and 2011, respectively. Variability in
soil characteristics, irrigation method, precipitation, and land
cover characteristics all contribute to variability in
evapotranspiration-driven per acre losses.

of surface water, reducing runoff losses and allowing water to
infiltrate into the soil. This water is available to plants as it
passes through the root zone. However, the re-routed water,
previously vulnerable to loss via surface flow, becomes
vulnerable to loss via subsurface flow pathways. Subsurface
flow pathways include: deep percolation to groundwater,
including groundwater return flow to surface water;
subsurface flow into a tile or ditch drainage system; lateral
subsurface outflow; and quick-return subsurface flow.
Conservation practices did not appreciably reduce overall
water losses, although the simulations suggest that dominant
water loss pathways have shifted due to conservation
adoption. Without any conservation practices in place, model
simulations suggest surface water runoff from cropped acres
in the region would average 10.1 inches per acre per year (24
percent of all water losses) and subsurface losses would
average 8.4 inches per acre per year (20 percent of all water
losses). Under conservation conditions of 2003-06 and 2011,
surface water runoff accounted for roughly 21 percent (8.8
inches per acre per year) and 20 percent (8.5 inches per acre
per year) of water losses from cropped acres, respectively
(table 3.1). Relative to the no-practice scenario, the surfacerunoff reducing practices in place in 2003-06 and 2011
decreased surface losses by 13 percent (1.3 inches per acre per
year) and 16 percent (1.6 inches per acre per year),
respectively. Subsurface flow losses accounted for 23 percent
(9.6 inches per acre per year) and 22 percent (9.3 inches per
acre per year) of all water losses from cropped acres in 200306 and 2011, respectively (table 3.1).
The reductions in surface losses were accomplished at the cost
of simultaneously increasing subsurface losses by 14 percent
(1.2 inches per acre per year) and 11 percent (0.9 inches per
acre per year), in 2003-06 and 2011, respectively.
The distribution of water losses via surface runoff (fig. 3.2)
and subsurface flow (fig.3.3) show the variability of these two
flow paths across the region’s variable soil types, cropping
systems, and conservation efforts.

Effects of Practices on Water Erosion and
Sediment Loss
Soil erosion and sedimentation are separate but interrelated
resource concerns. Soil erosion is the detachment and
transport of soil particles in the field, while sedimentation
describes the portion of the eroded material that settles in
areas onsite or offsite. Sediment loss describes the sediment
transported beyond the edge of the field by water. For the
purposes of this report, the “field” includes the cropped
portion of the field and any edge-of-field filtering and
buffering conservation practices. Controlling sheet and rill
erosion helps prevent sediment loss and sustain soil
productivity.

Structural water erosion control practices, residue
management practices, and conservation tillage slow the flow

39

Table 3.1. Field-level effects of conservation practices on water loss pathways on cropped acres in the Chesapeake Bay region: the
no-practice scenario, 2003-06 baseline condition, and 2011 conservation condition.
Model simulated outcome on cropped acres

Nopractice
Scenario

2003-06
Baseline

2011
Condition

42.3

42.3

42.3

42.7

42.7

43.1

7.5

7.5

7.0

24.3

24.2

24.9

Reduction:
No-practice to
2003-06

Reduction:
2003-06 to
2011

0.03

-0.7***

Water sources
Non-irrigated acres
Average annual precipitation (inches)
Irrigated acres
Average annual precipitation (inches)
Average annual irrigation water applied (inches)*
Water loss pathways
Average annual evapotranspiration (inches)

Average annual surface water runoff (inches)
10.1
8.8
8.5
1.3
0.3
Average annual subsurface water flows (inches) **
8.4
9.6
9.3
-1.2
0.3
(inches)practices remained fairly constant between the two surveys. Irrigation was practiced on 5 and 6 percent of the cropped acres in the Chesapeake Bay
* Irrigation
region in 2003-06 and 2011, respectively.
** Subsurface flow pathways include: (1) deep percolation to groundwater, including groundwater return flow; (2) subsurface flow into a drainage system; (3)
lateral subsurface outflow; and (4) quick-return subsurface flow.
*** Negative values connote an increase in losses rather than a reduction in losses. For example, this suggests an average increase in evapotranspiration losses of
0.7 inch per year (3 percent increase) for cropped acres due to the changes in conservation practices between 2003-06 and 2011.

Figure 3.2. Estimates of long-term average annual surface runoff losses of water on cropped acres in the Chesapeake Bay region: the
no-practice scenario, 2003-06 baseline condition, and 2011 conservation condition.
20

Average annual inches

15

10

5

0
0

10

20

30

40

50

60

70

80

90

100

Cumulative percent acres
No-Practice Scenario

2003-06 Baseline Condition

2011 Conservation Condition

40

Figure 3.3. Estimates of long-term average annual subsurface flow losses of water on cropped acres in the Chesapeake Bay region:
the no-practice scenario, 2003-06 baseline condition, and 2011 conservation condition.

Average annual inches

20

15

10

5

0
0

10

20

30

40

50

60

70

80

90

100

Cumulative percent acres
No-Practice Scenario

2003-06 Baseline Condition

Sediment loss, as estimated in this study, includes the portion
of the sheet and rill eroded material that settles offsite, as well
as sediment that originates from ephemeral gully erosion
processes.10 Sediment is composed of detached and
transported soil particles, organic matter, plant and animal
residues, and associated chemical and biological compounds,
including nutrients.
The full set of 2007 NRI points for cropped acres in this
region and the sample set from 2011 indicate slightly more
than 40 percent of the acres (1.75 million) are classified as
highly erodible land (HEL). The 2003-06 survey documented
44 percent HEL acres, which is within the margin of error.
Most of the HEL acres are located in the Appalachian
Highlands physiographic region (including the Piedmont
province, Appalachian Plateaus province, and Allegheny
Mountain section), where relatively shallow cropped soils tend
to occur on moderately sloping to steep landscapes. In these
more vulnerable landscapes, annual sediment losses can vary
considerably due to variability in storm intensity and length of
weather events.

10

For this study, the APEX model was set up to estimate sediment loss using
a modified version of USLE, called MUSLE, which uses an internal sediment
delivery ratio to estimate the amount of eroded soil that actually leaves the
boundaries of the field. A large percentage of the eroded material is
redistributed and deposited within the field or trapped by buffers and other
conservation practices and does not leave the boundary of the field, which is
taken into account in the sediment delivery calculation. The estimate also
includes some ephemeral gully erosion. For this reason, sediment loss rates
can exceed sheet and rill erosion rates.

2011 Conservation Condition

Sheet and rill erosion
Traditional conservation planning efforts to control sheet and
rill erosion focus on achieving a calculated soil loss tolerance
(T). The T value represents the maximum annual soil loss rate
at which current production levels are sustainable. Simulations
show that between 2003-06 and 2011, conservation efforts
made gains in reducing the incidences of field erosion losses
greater than T. Cropland on which losses greater than T
occurred were reduced from 28 to 11 percent of cropped acres
between 2003-06 and 2011 (table 3.2 and fig. 3.4). These
conservation gains were driven largely by the significant
reduction of HEL acres on which sheet and rill erosion
exceeded T, which dropped from 57 to 19 percent of HEL
acres between 2003-06 and 2011(table 3.2 and fig. 3.4).
Relative to a no-practice scenario, model simulations suggest
that conservation practices adopted in 2003-06 reduced sheet
and rill erosion by 51 percent, an average reduction of 3.9 tons
per acre per year. Relative to 2003-06 losses, conservation
practices adopted in 2011reduced sheet and rill erosion by an
additional 59 percent, an average reduction of 2.2 tons per
acre per year (table 3.3). In 2003-06, the 10 percent of cropped
acres most affected by sheet and rill erosion were losing more
than 10 tons of soil per acre per year. By 2011, only 3 percent
of acres were losing more than 10 tons of soil per year to sheet
and rill erosion.

41

Table 3.2. Assessment of sheet and rill erosion based on T.
2003-06
Acres
(1,000’s)

2011
Acres
(1,000’s)

2003-06
Percent
of Acres

2011
Percent
of Acres

2,468.1

2,467.2

86

95

14

5

NHEL

≤T

NHEL

>T

394.6

141.7

NHEL

all

2,862.7

2,608.9

HEL

≤T

611.1

1,412.1

43

81

HEL

>T

806.1

332.4

57

19

HEL

all

1,417.2

1,744.5

All

≤T

3,079.2

3,879.3

72

89

All

>T

1,200.7

474.1

28

11

All

All

4,279.9

4,353.4

Note: Erosion estimates were made with RUSLE2, within APEX. HEL are
highly erodible acres; NHEL are non-highly erodible acres. The full set of
NRI points for cropped acres in this region indicates slightly more than 40
percent of the acres are classified as HEL.

Simulations show that relative to a no-practice scenario, 200306 conservation practices reduced sheet and rill erosion losses
on highly erodible land (HEL) by 53 percent (8.7 tons per acre
per year) and on non-highly erodible land (NHEL) by 50
percent (1.6 tons per acre per year) (table 3.3). Relative to the
2003-06 conservation condition, the additional practices
adopted in 2011 reduced sheet and rill erosion losses on HEL
by 66 percent (5.0 tons per acre per year) and on NHEL by 50
percent (0.8 ton per acre per year).

Sediment loss due to water erosion
Reductions in sediment loss due to conservation practices are
much higher for some acres than others, reflecting both the
variability in the level of treatment applied and differences in
the inherent erodibility of the soil. Relative to a no-practice
scenario, model simulations suggest that conservation practices
adopted in 2003-06 reduced sediment losses by 54 percent, an
average reduction of 6.0 tons per acre per year. Relative to
2003-06 losses, conservation practices adopted in 2011 reduced
edge-of-field sediment losses by an additional 63 percent, an
average reduction of 3.2 tons per acre per year (table 3.3).
Model simulations show that under 2003-06 baseline conditions,
59 percent of cropped acres lost less than 2 tons of sediment per
acre per year and the 10 percent of cropped acres with the worst
sediment loss problems lost more than 15.7 tons of sediment per
acre per year. Under the 2011 conservation condition, 83
percent of cropped acres lost less than 2 tons of sediment per
acre per year and only 3 percent of cropped acres lost more than
15.7 tons of sediment per acre per year.
Simulations show that relative to a no-practice scenario, 200306 conservation practices reduced sediment losses on highly
erodible land (HEL) by 56 percent (14.0 tons per acre per
year) and on non-highly erodible land (NHEL) by 53 percent
(2.3 tons per acre per year) (table 3.3). Relative to the 2003-06
conservation condition, the additional practices adopted in
2011 reduced sediment losses on HEL by 68 percent (7.5 tons
per acre per year) and on NHEL by 60 percent (1.2 tons per
acre per year).
The model scenario in which cover crops were removed from
the 2011 conservation systems indicates that on average cover

crop use improved reduction of sediment losses by nearly 58
percent. Frequency of use made a substantial difference.
Annual adoption of cover crops improved sediment reduction
by 78 percent, while use at a frequency of one out of every
three years or more, but not annually, improved the sediment
reduction by 56 percent. Less frequent cover crop use still
provided sediment loss reduction improvements of 38 percent.
The annual use of cover crops and their effect on sediment
loss reduction illustrates the valuable conservation service
they provide in keeping the soil covered and protected from
fall and winter storm events.
The APEX simulations suggest that conservation practices
adopted between 2003-06 and 2011 had similar impacts on
surface water runoff (table 3.1). As noted above, relative to a
no-practice scenario, conservation practices adopted in 2003-06
and 2011 reduced surface water losses by 13 and 16 percent,
respectively. However, simulations suggest that during the same
time periods, conservation practices reduced sediment losses by
63 and 83 percent, relative to a no-practice scenario (table 3.3,
fig. 3.5). The lack of synchrony in conservation gains for
surface water and sediment loss indicates that the concentration
of sediment in surface water decreased between 2003-06 and
2011. In other words, although water losses were reduced by 13
and 16 percent, the water that was lost was not laden with
sediment. Sediment concentrations in surface water may have
been diminished by conservation practices that reduced rain
drop impacts, such as cover crop adoption and reduced tillage
practices. Conservation practices such as reduced tillage, cover
crops, and buffers also slow water runoff, allowing sediment to
fall out of suspension and be retained on the field.
Ironically, this cleaner surface water is less viscous and would
have higher erosive energy than would a similar volume of
sediment laden runoff. This phenomena is often observed within
in no till fields, where the residues intercepting the raindrop
impact produce cleaner runoff, which, when concentrated, can
produce ephemeral gully erosion. The cleaner, faster flowing
water would also have a greater capacity for picking up
previously deposited sediments. This potentially negative
impact that cleaner water has on gully formation is due to
positive conservation outcomes of sediment loss reduction
practices. This flow dynamic caused by the adoption of upland
erosion control practices will take time to stabilize before the
full benefit of the additional conservation practices are realized.
These complicated interactions demonstrate the importance of
comprehensive conservation planning.
In addition to reducing overall average annual sediment losses,
conservation practices put in place between 2003-06 and 2011
decreased the annual number and severity of significant single
storm events causing large losses. Instead of examining the
losses of a significant weather event such as a 25-year storm,
this analysis looks at the predicted sediment loss from strong
storms of any magnitude. Acreage with a sound conservation
management plan may have losses from a rare storm event
well below losses typical of acreage with a low level of
conservation and less intense storm. Sediments lost from these
significant events cause excessive damage to the environment
and tend to persist in the ecosystem, only to be re-suspended
months or years later with subsequent exceptional storms.

42

Figure 3.4. Estimates of long-term average annual sheet and rill erosion on cropped acres in the Chesapeake Bay region: the nopractice scenario, 2003-06 baseline condition, and 2011 conservation condition.

50

Average annual tons/acre

45
40
35
30
25
20
15
10
5
0
0

10

20

30

40

50

60

70

80

90

100

Cumulative percent acres
No-Practice Scenario

2003-06 Baseline Condition

2011 Conservation Condition

Table 3.3. Changes in average field-level effects of conservation practices on erosion and sediment loss on cropped acres in the
Chesapeake Bay region between 2003-06 and 2011.

Model simulated outcome

No-practice
(tons/acre

2003-06
(tons/acre)

2011
(tons/acre)

Reduction: Nopractice to
2003-06
(tons/acre)

7.6

3.7

1.5

3.9

2.2

11.1

5.1

1.9

6.0

3.2

16.3

7.6

2.6

8.7

5.0

25.0

11.0

3.5

14.0

7.5

3.2

1.6

0.8

1.6

0.8

4.3

2.0

0.8

2.3

1.2

Reduction: 200306 to 2011
(tons/acre)

Cropped acres
Average annual sheet and rill erosion*
Average annual sediment loss at edge-of-field
due to water erosion
Highly erodible land (HEL)
Average annual sheet and rill erosion*
Average annual sediment loss at edge-of-field
due to water erosion
Non-highly erodible land (NHEL)
Average annual sheet and rill erosion*
Average annual sediment loss at edge-of-field
due to water erosion

* Estimated using the Revised Universal Soil Loss Equation.
Note: Percent reductions were calculated prior to rounding the values for reporting in the table and the associated text.
Note: In the 2003-06 survey there were an estimated 1.87 million HEL acres (44 percent). The subset of NRI points for the 2011 survey had 1.75 million HEL acres (40
percent); a difference of 4 percent and also within the margins of error. The full set of NRI points for cropped acres in this region indicates slightly more than 40 percent
of the acres are HEL.

43

Figure 3.5. Estimates of long-term average annual sediment losses to water erosion on cropped acres in the Chesapeake Bay region:
the no-practice scenario, 2003-06 baseline condition, and 2011 conservation condition.

50

Average annual tons/acre

45
40
35
30
25

20
15

10
5
0
0

10

20

30

40

50

60

70

80

90

100

Cumulative percent acres
No-Practice Scenario

2003-06 Baseline Condition

2011 Conservation Condition

2 Tons per Acre Threshold

In this study, a system is considered adequately treated for
sediment if, over the 52 years of weather conditions, it loses
on average less than 2 tons of sediment per acre per year.
Figure 3.6 shows the average number of days each year in
which a storm event is predicted to produce more than 1 ton of
sediment loss. Acres on which sediment losses of this level
were predicted to occur on more than 2 days within one year
are considered lacking in adequate sediment conservation
treatment. In the no-practice scenario over 50 percent of the
acres have more than 2 tons of sediment loss from just two
storm events each year. Under 2003-06 conservation
conditions, simulations show 17 percent of cropped acres
would exceed the 2-ton loss threshold due to only two storm
events, each of which would cause a loss of 1 or more tons of
sediment. Relative to 2003-06, conservation practices adopted
in 2011 would decrease the acres experiencing annual losses
in excess of 2 tons due to two storm events to only 7 percent
of cropped acres. If adoption of suites of soil conservation
practices continue, these large single loss events are likely to
become less frequent (fig. 3.6).

Effects of Practices on Soil Organic Carbon
Soil organic carbon (SOC) reduces erodibility and improves
the soil’s structure, nutrient cycling capacity, water holding
capacity, and biotic integrity. The most practical way to
improve soil health is to manage for soil organic matter

(SOM). SOM enhances soil’s ability to perform all of its vital
functions, including maintaining crop production with
concurrent reduction in the potential for sediment, nutrient,
and pesticide losses. Because carbon is SOM’s primary
constituent, increasing SOM also sequesters carbon and
reduces atmospheric carbon dioxide, lessening agriculture’s
contribution to climate change.
In this study, estimation of soil organic carbon (SOC) change
assumes a starting point for the simulation based on soil
characterization data from soils impacted by years of
cultivation practices. To more appropriately approximate soil
carbon stores for the surveyed point’s soil map unit we used,
measured soil characterization data that included SOC from
pedons with evidence of tillage. The carbon data for these soil
characterization pedons was also compared to data collected
from the USDA NRCS Soil Science Division’s Rapid Carbon
Assessment (RaCA) project. To date over 35,000 sites across
multiple land uses have been sampled and analyzed for SOC.
The SOC for the soils used in this study were compared to the
middle 80 percent of the range of results for similar soils in
the RaCA database. Data falling outside the range were
adjusted to the median values found in the RaCA soils. These
more realistic starting carbon levels attempt to not impart
erroneous stores of organic nitrogen since SOM generally
maintains a carbon to nitrogen ratio of 10:1.

44

Figure 3.6. Estimates of average number of days each year in which a storm event produced more than 1 ton of sediment loss: the nopractice scenario, 2003-06 baseline condition, and 2011 conservation condition.

Days with sediment exceeding 1 ton

25

20

15

10

5

0
0

10

20

30

40

50

60

70

80

90

100

Cumulative percent acres
No-Practice Scenario

2003-06 Baseline Condition

Simulation modeling shows carbon management improved or
was maintained on all cropped acres in 2011, as compared to
2003-06. As noted previously, the widespread adoption of
high residue crop rotations, cover crops, structural practices,
and conservation tillage between 2003-06 and 2011 played a
significant role in the widespread positive changes in soil
carbon trends (table 3.4). It should be noted that annual SOC
dynamics and the impact of conservation practices on those
dynamics vary considerably among acres in the region.
The combination of high rainfall on sloping soils and mild
winters that allow rapid degradation of organic materials make
carbon accumulation challenging in the Chesapeake Bay
region. Further, the highly weathered, less reactive nature of
the soils in this region makes them vulnerable to carbon loss
under even moderately intense tillage. Therefore, the
maintenance of SOC requires a comprehensive conservation
plan on most acres. Maintaining adequate carbon levels is a
valuable conservation achievement. For the purposes of this
report, cropping systems are considered to be maintaining
SOC if average annual gains or losses do not exceed 100
pounds per acre per year. This rate of change is difficult to
detect in a short time period. It may take more than 20 years
for a 0.1 percent change in SOC to occur.
Model simulations show that in 2003-06 cultivated cropland
acres in the Chesapeake Bay region were on average losing
SOC at a rate of 189 pounds per acre per year (table 3.4). The
increased adoption of cover crops, conservation tillage, and
structural practices in 2011 reduced average SOC losses to 95
pounds per acre per year. Thus, adoption of the conservation

2011 Conservation Condition

practices in place in 2011 changed the overall trend in the
Chesapeake Bay region. Conditions on cultivated cropland in
the region were improved such that on average, acres went
from losing SOC to maintaining SOC.
The data in Table 3.4 is divided into categories denoting the
three potential soil organic carbon (SOC) trends: gaining,
maintaining, or losing. These categories are further stratified
by average tillage type for the crop rotation. Acreage gaining
more than 100 pounds of SOC per year increased by 9
percentage points, from only 3 percent of acres in 2003-06 to
12 percent in 2011. Not only were more acres gaining SOC in
2011 than in 2003-06, but acres gaining SOC were gaining an
average of 30 more pounds of SOC in 2011 than in 2003-06.
Acres maintaining SOC also increased, from 31 to 42 percent
of acres in 2003-06 and 2011, respectively. In both survey
periods, the average rate of SOC change on acres maintaining
SOC decreased from an average annual loss rate of 29 pounds
per acre per year in 2003-06 to 10 pounds per acre per year in
2011. The most significant change between the survey periods
was the 20 percentage point decline in acres losing SOC. In
2003-06, 66 percent of cultivated acres in the Chesapeake Bay
region were losing SOC at an average rate of 289 pounds per
acre per year. Under 2011 conservation conditions, 46 percent
of acres were losing an average of 245 pounds of SOC per
acre per year.
The model scenario removing cover crops only from 2011
conservation systems indicate that on average cover crop use
improved enhancement of soil organic carbon levels by 63
percent. Most conservation practices adopted to build SOC act

45

Table 3.4. Residue and tillage management practices in the Chesapeake Bay region, 2003-06 and 2011.

Residue and tillage management
practice in use

Average
Annual
STIR
value*

Acres
(1,000’s)

2003-06
Acres in
Average
Chesapeake Soil Carbon
Bay region
change
(percent) (lbs/acre/yr)

Acres
(1,000’s)

2011
Acres in
Chesapeake
Bay region
(percent)

Average
Soil Carbon
change
(lbs/acre/yr)

159
168
135
127

513.3
405.8
80.8
26.7

12
9
2
1

189
195
161
184

-29
-25
-33
-32

1,838.9
1,272.9
425.6
140.4

42
29
10
3

-10
-11
-5
-17

46
26
14
6

-245
-216
-249
-355

Acres gaining carbon
Acres gaining >100 lbs
carbon/acre/year
No-till acres
Mulch-till acres
Continuous conventional till acres

<20
20-80
>80

119.8
89.5
15.4
14.9

3
2
<1
<1

Acres maintaining carbon
Acres gaining or losing <100 lbs
carbon/acre/year
No-till acres
Mulch-till acres
Continuous conventional till acres

Acres losing >100 lbs carbon/acre/year
No-till acres
Mulch-till acres
Continuous conventional till acres
Total or Average

<20
20-80
>80

1,346.8
695.2
416.2
235.4

31
16
10
6

<20
20-80
>80

Acres losing carbon
2,813.3
66
963.2
23
957.8
22
892.2
21

-289
-235
-280
-329

2,001.2
1,126.4
608.4
266.4

4,279.9

-189

4,353.4

-95

* Average annual Soil Tillage Intensity Rating (STIR) over all crop years in the rotation.
Note: A description of the Soil Tillage Intensity Rating (STIR) can be found at http://stir.nrcs.usda.gov/.
Note: In the 2003-06 survey there were an estimated 1.87 million HEL acres (44 percent). The subset of NRI points for the 2011 survey had 1.75 million HEL acres (40
percent); a difference of 6 percent and also within the margins of error. The full set of NRI points for cropped acres in this region indicates slightly more than 40 percent
of the acres are HEL. Soils are classified as HEL if they have an Erodibility Index (EI) score of 8 or higher. A numerical expression of the potential of a soil to erode, EI
considers the physical and chemical properties of the soil and climatic conditions where it is located. The higher the index, the greater the investment needed to
maintain the sustainability of the soil resource base if intensively cropped.
Note: Percents may not add to totals because of rounding.

to preserve residues and prevent runoff losses. Cover crops
provide those benefits and add to the residue available for
conversion to soil organic matter (SOM). Relative to no use of
cover crops, annual adoption improved the average annual
change in soil carbon by 148 percent. Use at a frequency of
one out of every three years or more, but not annually,
improved the systems’ carbon enhancement by 53 percent,
while less frequent use still provided a 21 percent benefit to
carbon dynamics.
The average annual impact of conservation practices on SOC
dynamics varies among acres, as shown in table 3.4,
depending on the extent to which residue and nutrient
management is used, the local climate, and the soil’s inherent
potential to sequester carbon. Carbon loss is mitigated by
improved tillage and erosion control practices, both of which
reduce the physical factors that contribute to carbon loss.
However, SOM maintenance also depends on the function of
soil microbes. A diverse and well-functioning community of
soil microbes requires nutrient inputs, primarily nitrogen, to
enable the soil to maintain and gain SOC. Comprehensive
nutrient management plans need to consider not only the
inputs necessary to feed the crop, but also inputs required to

feed the soil microbes essential for soil health. Insufficient
nutrient availability can cause SOM to decline. This will in
turn release carbon and change the soil structure and function.
Soil physical properties will begin to breakdown, increasing
soil erosion and runoff losses.
The APEX model also estimates carbon lost from the soil
surface due to water and wind erosion (table 3.5). Changes in
conservation practices between 2003-06 and 2011 contributed
to a 109 pound per acre (27 percent) reduction in carbon lost
from the soil surface of cropped acres in the Chesapeake Bay
region. This carbon at the surface is a very important part of
the agroecological system: it helps protect the soil surface
from erosive forces, serves as an important part of the food
supply for soil organisms which maintain soil health, and
provides the material that eventually becomes part of the SOC
pool. Because of the relationship between carbon and nitrogen
use in the soil microbe communities, the observed annual onfield increase of 109 pounds of carbon (table 3.6) may confer
to the soil biota the ability to take up an additional 3 to 10
pounds of nitrogen, depending on the carbon to nitrogen ratios
of the residues and their stage of decomposition into the
organic fraction. The enhanced use of the nitrogen by the soil

46

conservation practices reduced carbon losses and/or
contributed to enhanced carbon gains in each of the four
runoff classes (table 3.5).This trend continued with the
enhanced conservation practice adoption in 2011 (fig. 3.7).
The gains noted in 2011 demonstrate the benefits of using
residue and tillage management in conjunction with structural
practices and cover crops. Not only did every runoff class
experience a 16 to 27 percentage point reduction in acres
losing SOC (table 3.5), but also the amount of carbon lost per
acre by runoff class decreased by between 75 and 107 pounds
per acre, with the greatest reductions in the moderately-high
runoff and the high runoff classes. Soils with low runoff
potentials realized the largest pound per acre gains in SOC.

communities prevents the nitrogen from being lost from the
system. Therefore, maintaining surface carbon enhances
healthy microbial communities in the soil, which in turn
provide an additional benefit to water quality while
simultaneously improving soil health. Compared to 2003-06
baseline conditions, nitrogen additions in the Chesapeake Bay
region increased by more than 14 pounds per acre on average
in 2011, but nitrogen and carbon losses both declined between
the two survey periods. This may be indicative of improved
SOM and associated soil health on cropped acres in the region.
Four runoff classes were devised for all cropped acres in the
Chesapeake Bay region based on inherent vulnerability to soil
erosion and associated nutrient losses through runoff (table
3.5). Relative to the no-practice scenario, 2003-06

Table 3.5. Field-level effects of conservation practices on carbon for cropped acres in the Chesapeake Bay region, 2003-06 and 2011.
Model simulated outcome

2003-06
(pounds/acre)

2011
(pounds/acre)

Reduction:
2003-06 to 2011
(pounds/acre)

Reduction:
2003-06 to 2011
(percent)

407

298

109

27

Cropped acres
Average annual carbon lost from the edge of the
agricultural management zone, including impacts of
edge-of-field conservation practices

Note: Percent reductions were calculated prior to rounding the values for reporting in the table and the associated text.
Note: Model simulation results for the baseline conservation condition are presented in Appendix E for the 4 subregions.

Table 3.6. Soil organic carbon dynamics by runoff class in the Chesapeake Bay region, 2003-06 and 2011.

Low
2003-06 2011

Moderate
2003-06 2011

Runoff Classes
Moderately High
2003-06
2011

High
2003-06

2011

All
2003-06

2011

Percent of acres Losing Carbon

54

35

79

52

66

50

83

64

66

46

Percent of acres Maintaining Carbon

43

49

21

41

30

39

13

30

31

42

3

17

0

6

4

11

3

5

3

12

Percent of acres Gaining Carbon

Note: Percents may not total to 100 because of rounding.

47

Figure 3.7. Estimates of long-term average annual change in soil organic carbon (SOC) on cropped acres in the Chesapeake Bay
region: the no-practice scenario, 2003-06 baseline condition, and 2011 conservation condition.
300

Average annual pounds/acre

200
100

0
-100
-200
-300
-400
-500
-600

0

10

20

30

40

50

60

70

80

90

100

Cumulative percent acres
No-Practice Scenario

2003-06 Baseline Condition

2011 Conservation Condition

100 Pounds per Acre Threshold

Effects of Practices on Nitrogen Loss
Plant-available nitrogen sources include applied commercial
fertilizer, applied manure, nitrogen produced by legume crops
(e.g., soybeans, alfalfa, beans, and peas), manure deposited by
grazing livestock, and atmospheric nitrogen deposition.
Simulation results suggest that relative to the no-practice
scenario the conservation practices on the ground in 2003-06
reduced annual nitrogen inputs by 15 percent, from 160.1 to
135.6 pounds per acre per year. Conservation practices
adopted in 2011 actually increased average annual nitrogen
inputs by 11 percent, from 135.6 to 149.9 pounds per cropped
acre per year (table 3.7). Although nitrogen inputs increased
between 2003-06 and 2011, roughly 66 percent of the nitrogen
inputs were taken up by the crop and removed at harvest in the
crop yield in both conditions. Crop use efficiency remained
relatively constant between the three scenarios, at 62 percent
for the no-practice scenario and 66 percent under both the
2003-06 and 2011 scenarios.
Acres with the highest nitrogen losses typically have the
highest inherent vulnerability combined with inadequate
nutrient management and runoff controls. Between 2003-06
and 2011, although annual nitrogen inputs increased by 11
percent (14.3 pounds per acre per year), the average amount of
total nitrogen lost from the field annually via all pathways,
other than the nitrogen removed from the field at harvest,
decreased by about 7 percent, dropping from 58.8 to 54.9
pounds per acre (table 3.7, fig. 3.8). These improvements in
nitrogen loss rates between 2003-06 and 2011 can be

attributed to the adoption of new conservation practices and
their impacts on various nitrogen loss pathways.
As expected, model simulation results showed that quantity of
nitrogen lost to specific pathways varies from acre to acre (fig.
3.8). Of all the nitrogen loss pathways, surface and subsurface
flows have the greatest potential to directly impact water
quality. Most nitrogen lost to subsurface flows returns to
surface water through drainage ditches, tile drains, natural
seeps, and groundwater return flow. Relative to a no-practice
scenario, the conservation practices adopted in 2003-06
reduced the cumulative total nitrogen lost via surface water
and subsurface flows by 29 percent, decreasing loss rates from
58.3 to 41.6 pounds per acre per year. Conservation conditions
adopted in 2011 reduced 2003-06 losses by 22 percent,
decreasing the average nitrogen loss rate to surface and
subsurface flows from 41.6 to 32.6 pounds per acre per year.
On average, the impact of the surface loss pathway for
nitrogen loss decreased with conservation practice adoption.
The surface loss pathway accounted for 36, 27, and 18 percent
of all nitrogen losses in the no-practice, 2003-06, and 2011
scenarios, respectively (table 3.7). While the role of the
surface loss pathway declined, the role of the subsurface loss
pathway remained fairly constant, accounting from 29, 44, and
42 percent of nitrogen losses in the no-practice, 2003-06, and
2011 scenarios, respectively. The decline in surface flow
losses in conjunction with the stability in subsurface losses is a
positive sign, considering that the achievements reducing

48

Table 3.7. Estimates of long-term average annual field-level effects of conservation practices on nitrogen sources and loss pathways
on cropped acres in the Chesapeake Bay region: the no-practice scenario, 2003-06 baseline condition, and 2011 conservation
condition.
Average annual values in pounds per acre
No-practice
Scenario

2003-06

2011

Nitrogen sources
Atmospheric deposition

8.8

8.8

8.9

Bio-fixation by legumes

31.9

31.8

Commercial fertilizer

94.9

73.0

Manure

24.6

Model simulated outcome

---Percent Change --No-practice to
2003-06
2003-06
to 2011

All cropped acres

All nitrogen sources

0

0.1

36.4

-0.1

4.6

79.7

-21.9

6.7

22.0

24.8

-2.6

2.8

160.1

135.6

149.9

-24.5

14.3

Nitrogen in crop yield removed at harvest

99.7

89.0

98.4

-10.7

9.4

Nitrogen loss pathways
Volatilization

18.4

14.2

17.4

-4.2

3.2

Denitrification processes

1.8

3.0

4.9

1.2

1.9

Windborne sediment

0.11

0.09

0.05

-0.02

-0.04

Surface runoff, including waterborne sediment

27.9

15.7

9.7

-12.2

-6.0

Surface water (soluble)

4.9

2.4

2.1

-2.5

-0.3

Waterborne sediment

23.0

13.3

7.6

-9.7

-5.7

Subsurface flow pathways

30.4

25.9

22.9

-4.5

-3.0

Total nitrogen loss for all loss pathways

78.4

58.8

54.9

-19.6

-3.9

-23.3

-17.2

-10.8

6.1

6.4

128.8

105.2

103.7

-23.6

-1.5

80.5

54.3

36.1

-26.2

-18.2

114.9

89.9

105.1

-25.0

15.2

47.3

35.5

30.3

-11.8

-5.2

161.7

133.3

130.8

-28.4

-2.5

78.8

58.9

40.5

-19.9

-18.4

95.0

72.8

80.8

-22.2

8.0

46.4

31.7

25.5

-14.7

-6.2

Change in soil nitrogen
Highly erodible land (HEL)
Nitrogen applied as commercial fertilizer and manure
Total nitrogen loss for surface and subsurface loss
pathways
Non-highly erodible land (NHEL)
Nitrogen applied as commercial fertilizer and manure
Total nitrogen loss for surface and subsurface loss
pathways
Acres with manure applied
Nitrogen applied as commercial fertilizer and manure
Total nitrogen loss for surface and subsurface loss
pathways
Acres without manure applied
Nitrogen applied as commercial fertilizer
Total nitrogen loss for surface and subsurface loss
pathways

** On about half of the cropped acres, more nitrogen volatilization and denitrification occurs with practices than without practices, resulting in only a small change in
nitrogen volatilization and denitrification on average for the region due to conservation practices. In preventing nitrogen loss to other loss pathways, conservation
practices keep more of the nitrogen compounds on the field longer, where they are exposed to wind and weather conditions that promote volatilization and
denitrification.
Note: Percent reductions were calculated prior to rounding the values for reporting in the table and the associated text. Model simulation results for the baseline
conservation condition are presented in Appendix E for the 4 subregions.

49

Figure 3.8. Estimates of long-term average annual total nitrogen losses on cropped acres in the Chesapeake Bay region: the nopractice scenario, 2003-06 baseline condition, and 2011 conservation condition.

Average annual pounds/acre

200
175
150
125
100
75

50
25
0
0

10

20

30

40

50

60

70

80

90

100

Cumulative percent acres
No-Practice Scenario

2003-06 Baseline Condition

surface flow reduction caused more nitrogen to be retained on
farm fields, making it more vulnerable to loss via subsurface
flow.
Acres classified as Highly Erodible Lands (HEL) received a
similar amount of total nitrogen inputs in both survey periods,
with 105.2 and 103.7 pounds per acre per year applied as
commercial fertilizer and/or manures in 2003-06 and 2011,
respectively. However, conservation practices reduced
nitrogen losses on HEL acres by 50 percent, or 18.2 pounds
per acre per year, between 2003-06 and 2011. On cropped
non-highly erodible land (NHEL), nitrogen application from
commercial fertilizer and manures increased by 14 percent, or
15.2 pounds per acre per year, but losses simultaneously
declined by 14 percent, or 5.2 pounds per acre per year. It is
important to note that not all the nitrogen available for loss
comes from intentionally applied fertilizers and manures; biofixed nitrogen and atmospheric nitrogen also contribute to the
pool of inputs upon which agricultural conservation practices
are acting.
Progress toward effective management of nutrient losses
associated with manured systems is demonstrated by the fact
that although the amount of nitrogen applied to acres receiving
manure remained unchanged between 2003-06 and 2011 (a
2.5-pound increase is within the margins of error), nitrogen
losses from manured fields declined by 18.4 pounds, or 45
percent over the same period (table 3.7). Between 2003-06 and
2011, the commercial-fertilizer-only acres saw an increase of
10 percent, or 8.0 pounds, in average annual nitrogen inputs

2011 Conservation Condition

and yet achieved a 24 percent, or 6.2 pound, reduction in the
amount of nitrogen lost. However, in absolute terms the
manured acres lost 40.5 pounds of nitrogen per acre per year
in 2011, while the non-manured acres lost 25.5 pounds per
acre. The disparity in pound per acre nitrogen loss rates
between manured and non-manured acres signifies the need
for a higher level of management when manure is part of the
cropping system.
Acres not receiving manure as part of their nutrient inputs had
nitrogen application rates 66.7, 60.5, and 50.0 pounds lower
than the average nitrogen application rate for manured fields
in the no-practice, 2003-06, and 2011 scenarios, respectively
(table 3.7). Similarly, non-manured acres had nitrogen loss
rates 32.4, 27.2, and 15.0 pounds lower than the average
nitrogen loss rate for manured fields in the no-practice, 200306, and 2011 scenarios.

Nitrogen lost via surface runoff
Conservation practices adopted in 2003-06 and 2011 were
effective at reducing nitrogen losses associated with runoff,
including nitrogen lost with waterborne sediment. Relative to
the no-practice scenario, conservation practices in place in
2003-06 reduced nitrogen losses in surface runoff by 44
percentage points, decreasing losses from 27.9 to 15.7 pounds
per acre per year. The conservation practices adopted in 2011
reduced nitrogen losses in surface runoff from 15.7 to 9.7
pounds per acre per year, a 38 percentage point reduction from
2003-06 loss rates (table 3.7; fig. 3.9). Conservation practice
adoption between the no-practice scenario and 2003-06 baseline

50

Figure 3.9 Estimates of long-term average annual nitrogen losses with surface runoff (including waterborne sediment) on cropped
acres in the Chesapeake Bay region: the no-practice scenario, 2003-06 baseline condition, and 2011 conservation condition.

Average annual pounds/acre

200
175
150
125
100
75
50
25
0
0

10

20

30

40

50

60

70

80

90

100

Cumulative percent acres
No-Practice Scenario

2003-06 Baseline Condition

2011 Conservation Condition

15 Pounds per Acre Threshold

condition reduced the percentage of acres on which surface
runoff losses exceeded 15 pounds of nitrogen annually from
60 to 37 percent of cropped acres. In the 2011 conservation
condition, only 18 percent of cropped acres experienced runoff
losses exceeding 15 pounds of nitrogen annually. The
significant increase in adoption of structural practices, cover
crops, and conservation tillage, contributed to the control and
trap aspects of the Avoid, Control, Trap (ACT) conservation
system strategy. These practices are largely responsible for the
reduction in nitrogen losses. There is still opportunity to
improve the avoidance aspect of ACT through better nutrient
application management, which, as discussed in Chapter 2,
was largely maintained at 2003-06 conservation levels. This
indicates that there is potential for more nutrient loss reduction
with improved nutrient application management. It is critical
to note that practices such as cover crops and conservation
tillage need to be maintained as active parts of the cropping
systems and management strategies if these gains are to be
continually realized in the future.
The model scenario removing cover crops only from the 2011
conservation systems indicates on average their use improved
reduction of nitrogen losses with surface flow by over 26
percent. Frequency of use made a substantial difference.
Annual use of cover crops improved nitrogen runoff
reductions by 40 percent and cover crop application at a
frequency of one out of every three years or more, but not
annually, reduced nitrogen loss to surface flow by 23 percent.
Less frequent use of cover crops still provided up to 19
percent reductions in nitrogen loss to surface flows. The
annual use of cover crops reduces nitrogen runoff losses by

scavenging carryover nutrients so that they cannot be lost with
runoff and by providing protective soil cover over the fall and
winter. The efficacy of cover crop adoption, even at nonannual adoption rates, demonstrates the critical value provided
by this practice in reducing impacts of nitrogen runoff on
water quality, particularly in fall and winter storm events.

Nitrogen lost via subsurface flow
Simulation modeling shows the subsurface flow pathway was
the dominant nitrogen loss pathway under all three simulated
scenarios. Roughly 39, 44, and 42 percent of total nitrogen lost
was lost via subsurface flow in the no-practice, 2003-06, and
2011 scenarios, respectively. The continued dominant role of
this loss pathway is a consequence of conservation practice
success in preventing edge-of-field nitrogen losses. However,
there have been conservation gains in decreasing nitrogen
losses to subsurface flows. Between the no-practice scenario
and the 2003-06 baseline condition, nitrogen losses to
subsurface flow pathways decreased by 15 percentage points,
from an average loss rate of 30.4 to 25.9 pounds per acre per
year. The 2011 conservation condition decreased the loss rate
by 13 percentage points, from 25.9 to 22.9 pounds per acre per
year (table 3.7, fig. 3.10). These reductions are not as large as
those observed for the surface flow loss pathway. This is not
unexpected given that nitrogen application management was
maintained at 2003-06 levels in 2011 (Chapter 2). The
subsurface losses are also being impacted by improved runoff
control measures, which redirect water and nutrients into the
soil, making them vulnerable to leaching losses. In the nopractice scenario 52 percent of nitrogen losses associated with

51

Figure 3.10. Estimates of long-term average annual nitrogen losses in subsurface flow on cropped acres in the Chesapeake Bay
region: the no-practice scenario, 2003-06 baseline condition, and 2011 conservation condition.

Average annual pounds/acre

100

75

50

25

0
0

10

20

30

40

50

60

70

80

90

100

Cumulative percent acres
No-Practice Scenario

2003-06 Baseline Condition

2011 Conservation Condition

25 Pounds per Acre Threshold

water movement were by subsurface pathways. The
conservation in place 2003-06 decreased surface losses, but
increased subsurface losses to account for 62 percent of water
related nitrogen losses and the improved runoff control in
2011 increased the proportion to 69 percent. Improving
nutrient management plans and better adherence to the 4Rs as
part of a more robust ACT conservation strategy will provide
opportunity for significant conservation gains.
These model simulation results underscore the importance of
pairing water erosion control practices with effective nutrient
management practices so that the full suite of conservation
practices work in concert to provide the environmental
protection needed. Although overall conservation practice
adoption reduced nitrogen losses to surface and subsurface
flows, management opportunities remain. For a small percent
of cropped acres, adoption of effective structural conservation
practices to treat surface flow losses may result in small
increases in nitrogen loss via subsurface flow. While our
results indicate that even with this re-routing of nutrients, the
reduction in surface losses of nitrogen typically far exceed the
increased subsurface nitrogen losses, these acres present
important nutrient management opportunities A commonly
effective way of addressing excess losses from leaching is to
better manage the rate, time, method, and form of application
of nutrients and irrigation water.

for crops to utilize the nitrogen by moving the nutrient through
its root zone, but may also impact water quality. A recent
USGS study determined that more than a quarter of the
nitrogen currently in the groundwater in the Delmarva
Peninsula in the Chesapeake Bay watershed may continue to
contribute nitrogen to the Chesapeake Bay for more than 50
years (Sanford and Pope 2013, accepted). A comprehensive
conservation plan should include cover crops as a means of
reducing subsurface losses by scavenging carryover nitrogen
in the soil and preventing its loss during the fall and winter
months. Model results from the scenario removing cover crops
demonstrate that on average, annual use of cover crops
reduced subsurface nitrogen losses by 35 percent. When
utilized less frequently than annually but at least one out of
every three years, cover crop application reduced the average
percentage of nitrogen lost in subsurface flows by 20 percent
compared to losses without cover crop management. Cover
crops provided benefits even when applied less frequently
than one out of three years, but at least once every five years;
in this scenario average cover crop adoption reduced annual
subsurface nitrogen losses by 9 percent. It should be noted
these are average reductions across all cropping systems and
nutrient management strategies. Reduction amounts varied
greatly due to geography and other management and
conservation practices.

Other nitrogen loss pathways
Practices that control runoff tend to redirect flow and increase
subsurface losses of nitrogen. This improves the opportunity

Nitrogen loss via volatilization and denitrification can be
undesirable, but does not directly impact water quality. Most

52

of the gaseous losses are in the N2 form, but there is risk of
some increased NOx greenhouse gas emissions. The role of
volatilization remained constant between the no-practice and
2003-06 scenarios, accounting for 23 and 24 percent of all
nitrogen losses (table 3.7). However, under conservation
practices in place in 2011, the role of volatilization increased
by 8 percentage points and accounted for 32 percent of all
nitrogen losses from cultivated cropland in the Chesapeake
Bay region. This increase is likely due in large part to the
increased use of manure in the region. Increased infiltration
rates resulting from successful control of surface runoff will
increase the frequency in which subsurface horizons reach
saturation, which will tend to promote denitrification. The role
of the denitrification pathway remained small, but increased
slightly across all scenarios, accounting for 2, 5, and 9 percent
of nitrogen losses in the no-practice, 2003-06, and 2011
scenarios, respectively.

acre to acre (fig. 3.11). Unlike nitrogen, phosphorus has no
gaseous loss pathways. Therefore, nearly all phosphorus
losses, whether they are via surface flow or subsurface flow,
have a high potential to impact water quality. Most
phosphorus lost to subsurface flows returns to surface water
through drainage ditches, tile drains, natural seeps, and
groundwater return flow. Relative to a no-practice scenario,
the conservation practices adopted in 2003-06 reduced the
cumulative total phosphorus lost via surface water and
subsurface flows by 57 percent, decreasing cumulative loss
rates from 8.0 to 3.4 pounds per acre per year. Conservation
conditions adopted in 2011 reduced 2003-06 losses by 44
percent, decreasing the average phosphorus loss rate to surface
and subsurface flows from 3.4 to 1.9 pounds per acre per year.
These practices also contributed to the increased rate of
accumulation of soil phosphorus, which rose from 0.5 to 2.6
pounds per acre between 2003-06 and 2011 (table 3.8).

Effects of Practices on Phosphorus Loss

These changes in soil phosphorus reflect the impacts of
conservation management reported in the 2003-06 and 2011
survey periods. These results are not derived from actual soil
test results for the farm fields. The appropriateness of a
phosphorus management plan can only be determined with the
trend compared to the soil test recommendation. For example,
a negative trend coupled with a high soil test phosphorus level
would indicate a sound nutrient management plan for reducing
the risk of water quality impairment. However, the same
negative trend with low soil test phosphorus could lead to
unsustainably mining the soil and would be detrimental to
both soil health and crop productivity. The significant change
in the soil phosphorus levels from 2003-06 to 2011, while a
good sign of retaining more phosphorus on the land, indicates
that producers need to be more aware of their soil phosphorus
and align their annual phosphorus management plans with
their soil test phosphorus results to reduce the risk of
impacting water quality.

Phosphorus, like nitrogen, is an essential element needed for
crop growth. Unlike nitrogen, however, phosphorus rarely
occurs in a gaseous form, so the APEX model does not
include an atmospheric component for simulation of
phosphorus dynamics. Although total phosphorus is plentiful
in the soil, only the small water-soluble fraction is available at
any one time for plant uptake. Farmers apply commercial
phosphate fertilizers and manures to supplement low
quantities of plant-available phosphorus in the soil.
Simulation results suggest that relative to the no-practice
scenario the conservation practices on the ground in 2003-06
reduced annual phosphorus inputs by 31 percent, from 34.6 to
23.8 pounds per acre per year. Conservation practices adopted
in 2011 actually increased average annual phosphorus inputs
by 6 percent, from 23.8 to 25.2 pounds per cropped acre per
year (table 3.8). Although phosphorus inputs increased
between 2003-06 and 2011, 62 and 63 percent of the
phosphorus inputs were taken up by the crop and removed at
harvest in the crop yield in 2003-06 and 2011, respectively.
Conservation practice adoption clearly improved crop use
efficiency, which increased from 48 percent under the nopractice scenario to 62 and 63 percent under both the 2003-06
and 2011 scenarios, respectively.
Acres with the highest phosphorus losses typically have the
highest inherent vulnerability combined with inadequate
nutrient management and runoff controls. Between 2003-06
and 2011, although annual phosphorus inputs increased by 6
percent (1.4 pounds per acre per year), the average amount of
total phosphorus lost from the field annually via all pathways,
other than the phosphorus removed from the field at harvest,
decreased by about 44 percent, dropping from 3.4 to 1.9
pounds per acre (table 3.8, fig. 3.11). These improvements in
phosphorus loss rates between 2003-06 and 2011 can be
attributed to the adoption of new conservation practices and
their impacts on various phosphorus loss pathways.

While there is no significant change in the role of the surface
loss pathway in phosphorus losses, the emerging trend
suggests conservation practices on the ground are reducing the
role of this pathway. Under the 2003-06 baseline condition,
the surface loss pathway accounted for 97 percent of
phosphorus losses, which was no different from the nopractice scenario, in which the surface loss pathway accounted
for 99 percent of phosphorus losses. Under the conservation
practices adopted in 2011, the role of the surface loss pathway
accounted for 94 percent of phosphorus losses (table 3.8).
Acres classified as Highly Erodible Lands (HEL) received the
same amount of total phosphorus inputs, 26.2 pounds per acre,
in both survey periods. However, conservation practices
reduced phosphorus losses on HEL acres by 57 percent, or 3.8
pounds per acre per year, between 2003-06 and 2011. On the
cropped non-Highly Erodible Lands (NHEL), phosphorus
application from fertilizer and manures increased by 8 percent,
or 1.8 pounds per acre per year , but losses simultaneously
declined by 33 percent, or 0.6 pounds per acre per year.

As expected, model simulation results showed that the
quantity of phosphorus lost to specific pathways varies from

53

Table 3.8. Estimates of long-term average annual field-level effects of conservation practices on phosphorus sources and loss
pathways on cropped acres in the Chesapeake Bay region: the no-practice scenario, 2003-06 baseline condition, and 2011
conservation condition.
Average annual values in pounds per acre
---Percent Change--Model simulated outcome

No-practice
Scenario

2003-06

30.4

20.1

2011

No-practice
to 2003-06

2003-06
to 2011

21.1

-10.3

1.0

Cropped acres
Phosphorus sources
Commercial fertilizer

4.2

3.7

4.1

-0.5

0.4

Total Phosphorus inputs

Manure

34.6

23.8

25.2

-10.8

1.4

Phosphorus in crop yield removed at harvest

16.7

14.8

15.8

-1.9

1.0

Phosphorus loss pathways
Windborne sediment

0.02

0.01

0.01

-0.01

<0.01

Surface water (sediment attached and soluble)*

7.9

3.3

1.8

-4.6

-1.5

Surface water (soluble)

1.1

0.5

0.5

-0.6

<0.01

Waterborne sediment

6.8

2.8

1.3

-4.0

-1.5

Subsurface flow pathways

0.1

0.1

0.1

<0.01

<0.01

Total phosphorus loss for all loss pathways

8.0

3.4

1.9

-4.6

-1.5

4.3

0.5

2.6

-3.8

2.1

Highly erodible land (HEL)
Phosphorus applied as commercial fertilizer and manure
Total phosphorus loss for surface and subsurface loss
pathways

34.4

26.2

26.2

-8.2

<0.01

15.2

6.7

2.9

-8.5

-3.8

Non-highly erodible land (NHEL)
Phosphorus applied as commercial fertilizer and manure
Total phosphorus loss for surface and subsurface loss
pathways

34.7

22.7

24.5

-12

1.8

4.4

1.8

1.2

-2.6

-0.6

Acres with manure applied
Phosphorus applied as commercial fertilizer and manure
Total phosphorus loss for surface and subsurface loss
pathways

46.8

39.0

35.6

-7.8

-3.4

8.9

4.2

2.2

-4.7

-2.0

-12.5

0.6

-4.6

-1.3

Change in soil phosphorus

Acres without manure applied
Phosphorus applied as commercial fertilizer
27.6
15.1
15.7
Total phosphorus loss for surface and subsurface loss
pathways
7.5
2.9
1.6
Note: Percent reductions were calculated prior to rounding the values for reporting in the table and the associated text.

54

Figure 3.11. Estimates of long-term average annual total phosphorus losses on cropped acres in the Chesapeake Bay region: the nopractice scenario, 2003-06 baseline condition, and 2011 conservation condition.

Average annual pounds/acre

32
28
24

20
16
12
8
4
0
0

10

20

30

40

50

60

70

80

90

100

Cumulative percent acres
No-Practice Scenario

2003-06 Baseline Condition

2011 Conservation Condition

3 Pounds per Acre Threshold

As with nitrogen, total phosphorus application rates are much
higher for cropped acres on which manure is part of the
nutrient management plan than on acres relying solely on
commercial phosphorus inputs (table 3.8). Progress toward
effective management of nutrient losses associated with
manured systems is demonstrated by the fact that the amount
of phosphorus applied to acres receiving manure fell by 9
percent, or 3.4 pounds per acre between 2003-06 and 2011.
Phosphorus losses from manured fields also declined by 2.0
pounds, or 48 percent, over the same period (table 3.8).
Between 2003-06 and 2011, the commercial-fertilizer-only
acres had no appreciable change in annual phosphorus inputs
and achieved a 45 percent, or 1.3 pound, reduction in the
amount of phosphorus lost. However, in absolute terms the
manured acres lost 2.2 pounds of phosphorus per acre per year
in 2011, while the non-manured acres lost only 1.6 pounds per
acre per year. The disparity in pound per acre phosphorus loss
rates between manured and non-manured acres is not as great
as the nitrogen disparity in manured and non-manured acre
losses. However, it still signifies the need for a higher level of
management when manure is part of the cropping system.
Acres not receiving manure as part of their nutrient inputs had
phosphorus application rates 19.2, 23.9, and 19.9 pounds
lower than the average nitrogen application rate for manured
fields in the no-practice, 2003-06, and 2011 scenarios,
respectively (table 3.8). Similarly, non-manured acres had
phosphorus loss rates 1.4, 1.3, and 0.6 pounds lower than the
average phosphorus loss rates for manured fields in the nopractice, 2003-06, and 2011 scenarios, respectively. It is

noteworthy that in all cases, the manured acres lost a lower
percentage of the phosphorus applied than did the nonmanured acres. The manured acres lost 19, 11, and 6 percent
of phosphorus applied in the no-practice, 2003-06, and 2011
scenarios, respectively. The non-manured acres lost 27, 19,
and 10 percent of applied phosphorus in the no-practice, 200306, and 2011 scenarios, respectively.

Phosphorus lost via surface runoff
Surface runoff was the dominant loss pathway for phosphorus,
accounting for 99, 97, and 94 percent of all phosphorus losses
in the no-practice, 2003-06, and 2011 scenarios, respectively.
Data suggest the role of the loss pathway is diminishing, but in
2011 it was still responsible for 94 percent of all phosphorus
losses. However, conservation practices adopted in 2003-06
and 2011 were effective at reducing pounds per acre
phosphorus losses associated with runoff, including both
soluble and sediment-bound phosphorus. Relative to the nopractice scenario, conservation practices in place in 2003-06
reduced phosphorus losses in surface runoff by 58 percentage
points, decreasing losses from 7.9 to 3.3 pounds per acre per
year. The conservation practices adopted in 2011 reduced
phosphorus losses in surface runoff from 3.3 to 1.8 pounds per
acre per year, a 46 percentage point reduction from 2003-06
loss rates (table 3.8).
Within the surface loss fraction, phosphorus bound to
sediment accounts for the majority of the phosphorus lost. Of
all lost phosphorus, the sediment bound phosphorus lost in
surface flow accounted for 85, 82, and 68 percent of

55

phosphorus losses in the no-practice, 2003-06, and 2011
scenarios, respectively. Since phosphorus tends to move with
sediment, these reductions in phosphorus losses may be
interpreted as a direct result of the controlling and trapping
practices adopted between 2003-06 and 2011, such as
increased adoption of cover crops, structural practices (such as
filters and buffers), and reduced tillage. Opportunities remain
to augment these improvements in the controlling and trapping
aspects of the Avoid, Control, Trap (ACT) conservation
strategy with practices that avoid nutrient losses. Changes in
phosphorus application management likely played little role in
achieving the observed loss reductions, but improved
phosphorus application management could provide future
conservation gains.
There is still opportunity to improve the avoidance aspect of
ACT through better nutrient application management, which,
as discussed in Chapter 2, was largely maintained at 2003-06
conservation levels. Although conservation practices adopted
between 2003-06 and 2011 made demonstrable gains on
reducing sediment associated phosphorus losses in surface
runoff, the soluble fraction of phosphorus lost in surface
runoff remained constant, maintaining an average loss rate of
0.5 pounds per acre. Because of the 44 percent reduction in
total phosphorus losses, the role of the surface loss pathway in
relation to soluble phosphorus loss increased in relevance,
accounting for 15 percent of losses in 2003-06, but 26 percent
of losses in 2011 (table 3.8). This indicates that there is
potential for more nutrient loss reduction with improved
nutrient application management. It is critical to note that
practices such as cover crops and conservation tillage need to
be maintained as active parts of the cropping systems and
management strategies if these gains are to be continually
realized in the future.
Conservation practice adoption between the no-practice
scenario and 2003-06 scenario reduced the percentage of acres
on which surface runoff losses exceeded 3 pounds of
phosphorus annually from 66 to 31 percent of cropped acres.
In the 2011 conservation condition, only 15 percent of
cropped acres experienced runoff losses exceeding 3 pounds
of phosphorus annually. While these trends are promising, the

number of acres exceeding the 3-pound threshold
demonstrates opportunity for continued conservation gains in
phosphorus loss reduction.
The model scenario removing cover crops only from the 2011
conservation systems indicates on average their use improved
reduction of phosphorus losses by 36 percent. Frequency of
use did not substantially impact efficacy of cover crop
adoption in improving phosphorus loss reduction. Annual use
of cover crops improved phosphorus reduction by 30 percent,
while application of cover crops at a frequency of one out of
every 3 years or more, but not annually, provided phosphorus
loss reductions of 28 percent. Relative to no cover crop
adoption, less frequent cover crop use reduced phosphorus
losses by up to 19 percent. The cause for the lesser impact of
cover crop adoption on phosphorus losses relative to sediment
and nitrogen losses is unclear, but may be related to
application timing with respect to crop needs and runoff
events. There is a significantly lower risk of phosphorus loss
to subsurface flows due to its much lower mobility relative to
nitrogen.

Phosphorus lost via subsurface flow
The subsurface flow pathway accounts for very little
phosphorus loss under all three simulated scenarios. Roughly
1, 3, and 5 percent of phosphorus lost was lost via subsurface
flows in the no-practice, 2003-06, and 2011 scenarios,
respectively. The trend towards increasing importance of this
pathway is due to conservation successes that have reduced
overall phosphorus losses. In fact, this loss pathway accounted
for an average of 0.1 pounds of phosphorus loss per acre per
year under all three scenarios.
These model simulation results underscore the importance of
pairing water erosion control practices with effective nutrient
management practices so that the full suite of conservation
practices work in concert to provide the environmental
protection needed.

56

Chapter 4
Assessment of Conservation
Treatment Needs
The conservation practices in use in the Chesapeake Bay
region during 2003-06 and 2011 were evaluated to identify the
long-term impact of the practices on sediment and nutrient
losses and to estimate conservation treatment needs for
controlling sediment and nutrient losses from fields.
Four resource concerns were evaluated for the Chesapeake
Bay region:
 Sediment loss due to water erosion;
 Nitrogen loss with surface runoff (nitrogen attached to
sediment and in solution);
 Nitrogen loss via subsurface flow pathways; and
 Phosphorus loss (phosphorus attached to sediment and
in solution in surface water and soluble phosphorus in
subsurface flow pathways).
Adequate treatment for each resource concern is site-specific
and is achieved by adopting conservation practices that treat
the specific inherent vulnerability factors associated with each
field. Not all acres require the same level of conservation
treatment and a singular practice, or even a given suite of
practices, will not provide the same amount of conservation
benefit for all acres. Acres with high inherent vulnerability
require more treatment than do less vulnerable acres. Acres
with characteristics such as steeper slopes and soil types that
promote surface water runoff are more vulnerable to sediment
and nutrient losses beyond the edge of the field via overland
flow losses. Acres that are essentially flat and have porous soil
types are more prone to nutrient losses through subsurface
flow pathways, most of which return to surface water through
drainage ditches, tile drains, natural seeps, and groundwater
return flow.
Model results suggest that adoption of structural practices
intended to reduce sediment losses coupled with adoption of
practices intended to reduce nutrient losses had significant
impacts in the Chesapeake Bay region between 2003-06 and
2011. Acres requiring additional treatment for one or more
resource concerns declined from 59 to 46 percent of acres.
Although gains have been made, roughly half of the acres in
the region still require additional treatment for one or more
resource concerns. Further, acres that are adequately treated
require continued conservation planning and management to
maintain current conservation gains. In summary, APEX
simulations for the Chesapeake Bay region indicate the
following changes due to conservation practice adoption
between 2003-06 and 2011:
 Acres requiring additional treatment to control
sediment runoff losses: were reduced by 28 percentage
points, dropping from 43 to 15 percent of acres;
 Acres requiring additional treatment to control nitrogen
runoff: were reduced by 21 percentage points,
dropping from 35 to 14 percent of acres;

 Acres requiring additional treatment to control
subsurface nitrogen losses: increased by 11 percentage
points, from 25 to 36 percent of acres; and
 Acres requiring additional treatment to control
phosphorus losses: were reduced by 18 percentage
points, from 30 to 12 percent of acres.

Conservation Treatment Levels
In this study, treatment needs for cropped acres in the
Chesapeake Bay region were estimated by cross-referencing
conservation treatment levels (defined by the type and
combinations of conservation practices documented in the
2003-06 and 2011 surveys) with inherent vulnerability
potentials (which reflect inherent risks to soils and nutrients
due to soil properties and landscape characteristics).
Conservation treatment criteria have been refined since the
previous report (USDA NRCS 2011). The assessment of
conservation treatment needs for the 2003-06 period was reanalyzed according to the improved criteria. Therefore, the
findings reported here for that survey period differ from those
previously reported.
Four levels of conservation treatment (high, moderately high,
moderate, and low) were defined for each resource concern:
 Sediment loss due to water erosion: conservation
treatment levels were defined by a combination of
structural practices, cover crops, and residue and tillage
management practices (fig. 4.1);
 Nitrogen loss with surface water runoff: conservation
treatment levels were defined by a combination of
structural practices, cover crops, residue and tillage
management practices, and nitrogen application
management practices (fig. 4.2);
 Nitrogen loss via subsurface flow: conservation
treatment levels were defined by a combination of the
level of residue produced by the full crop rotation and
nitrogen application management practices (figs. 2.3
and 4.3); and
 Phosphorus loss with surface water runoff:
conservation treatment levels were defined by a
combination of structural practices, cover crops,
residue and tillage management practices, and
phosphorus application management practices (figs. 2.6
and 4.4).
When not exposed to excessive tillage, high residue crop
rotations, especially those with cover crops, tend to retain
more nutrients in the organic fractions of the soil, thereby
reducing the amount of nutrients lost to ground and surface
waters. Cropped acres managed with a high treatment level
typically maintained significantly reduced sediment and
nutrient losses as compared to acres with lower levels of
treatment (tables 4.1 through 4.4).

Sediment Losses
Marked increases in levels of treatment and associated
sediment-related conservation gains were largely driven by
significant increases in adoption of structural practices, cover
crops, and conservation tillage (Chapter 3).

57

Percent of cropped acres

Figure 4.1. Percent of cropped acres in each conservation treatment level for water erosion control in the Chesapeake Bay region,
2003-06 and 2011.
50
45
40
35
30
25
20
15
10
5
0

Low

Moderate

Moderately High

High

2003-06

37

49

13

2

2011

13

38

34

16

Figure 4.2. Percent of cropped acres in each conservation treatment level for nitrogen runoff control in the Chesapeake Bay region,
2003-06 and 2011.
50
Percent of cropped acres

45
40
35
30
25
20
15
10
5
0

Low

Moderate

Moderately High

High

2003-06

11

36

44

8

2011

5

21

40

35

58

Figure 4.3. Percent of cropped acres in each conservation treatment level for nitrogen leaching control in the Chesapeake Bay
region, 2003-06 and 2011.
50
Percent of cropped acres

45
40
35
30
25
20
15
10
5
0

Low

Moderate

Moderately High

High

2003-06

14

23

50

11

2011

12

24

46

19

Figure 4.4. Percent of cropped acres in each conservation treatment level for phosphorus runoff control in the Chesapeake Bay region,
2003-06 and 2011.
45
Percent of cropped acres

40
35
30
25
20
15
10
5
0

Low

Moderate

Moderately High

High

2003-06

15

23

41

20

2011

10

16

36

38

59

Table 4.1. Estimated average annual sediment loss for levels
of soil runoff potential by levels of conservation treatment,
Chesapeake Bay region (2011 conservation condition).
Runoff
Potential

Sediment Treatment Level
(tons/acre)
Low

Moderate

Mod. High

High

Low

3.1

0.8

0.5

0.2

Moderate

7.8

1.3

1.0

0.3

9.3

1.8

0.8

0.2

19.8

6.6

2.3

4.4

Mod. High
High

Table 4.2. Estimated average annual nitrogen loss with surface
runoff for levels of soil runoff potential by levels of conservation
treatment, Chesapeake Bay region (2011 conservation condition).
Nitrogen Runoff Treatment Level
(pounds/acre)

Runoff
Potential

Low

Moderate

Mod. High

High

Low

14.0

8.2

6.7

3.9

Moderate

13.5

18.5

10.8

6.8

Mod. High

31.5

17.9

11.2

8.0

High

38.4

28.3

21.3

12.6

Table 4.3. Estimated average annual nitrogen loss in subsurface
flows for levels of soil leaching potential by levels of conservation
treatment, Chesapeake Bay region (2011 conservation condition).
Nitrogen Leaching Treatment Level
(pounds/acre)

Leaching
Potential

Low

Moderate

Mod. High

High

Low

26.4

29.7

13.6

10.7

Moderate

47.5

27.1

17.1

16.6

Mod. High

36.1

29.9

16.0

10.6

High

71.1

34.0

29.9

10.9

Table 4.4. Estimated average annual phosphorus loss to surface
water for levels of soil runoff potential by levels of conservation
treatment, Chesapeake Bay region (2011 conservation condition).
Runoff
Potential

Phosphorus Runoff Treatment Level
(pounds/acre)
Low

Moderate

Mod. High

High

Low

4.0

1.8

1.0

0.6

Moderate

3.7

3.0

2.3

1.1

Mod. High

6.8

3.8

2.1

1.0

High

8.6

7.4

4.8

1.9

Model simulations demonstrated the following changes in
conservation treatment levels for sediment losses due to water
erosion on cropped acres in the Chesapeake Bay region in the
2003-06 baseline condition and 2011 conservation condition
(fig. 4.1 and table 4.5):
 Acres receiving a high treatment level of water erosion
control: 14 percentage point increase, from 2 to 16
percent of cropped acres;

 Acres receiving a moderately high treatment level of
water erosion control: 21 percentage point increase,
from 13 to 34 percent of cropped acres;
 Acres receiving a moderate treatment level of water
erosion control: 11 percentage point decrease, from 49
to 38 percent of cropped acres; and
 Acres receiving a low treatment level of water erosion
control: 24 percentage point decrease, from 37 to 13
percent of cropped acres.
Declines in the number of acres in the low and moderate
treatment level categories are a positive trend. These declines
demonstrate that more acres are receiving higher levels of
treatment to prevent sediment losses.

Nitrogen Losses
Model simulations demonstrated the following changes in
conservation treatment levels for nitrogen losses via surface
water pathways on cropped acres in the Chesapeake Bay
region in the 2003-06 baseline condition and 2011
conservation condition (fig. 4.2 and table 4.6):
 Acres receiving a high treatment level of surface
nitrogen loss controls: 27 percentage point increase,
from 8 to 35 percent of cropped acres;
 Acres receiving a moderately high treatment level of
surface nitrogen loss controls: maintained 2003-06
conservation treatment levels, at 44 and 40 percent of
cropped acres;
 Acres receiving a moderate treatment level of surface
nitrogen loss controls: 15 percentage point decrease,
from 36 to 21 percent of cropped acres; and
 Acres receiving a low treatment level of surface
nitrogen loss controls: 6 percentage point decrease,
from 11 to 5 percent of cropped acres.
Declines in the number of acres in the low and moderate
treatment level categories are a positive trend. These declines
demonstrate that more acres are receiving higher levels of
treatment to prevent nitrogen losses in surface runoff.
Model simulations demonstrated the following changes in
conservation treatment levels for nitrogen losses via
subsurface flow pathways on cropped acres in the Chesapeake
Bay region in the 2003-06 baseline condition and 2011
conservation condition. (fig. 4.3 and table 4.7):
 Acres receiving a high treatment level of subsurface
nitrogen loss controls: 8 percentage point increase,
from 11 to 19 percent of cropped acres;
 Acres receiving a moderately high treatment level of
subsurface nitrogen loss controls: maintained 2003-06
conservation treatment levels, at 50 and 46 percent of
cropped acres;
 Acres receiving a moderate treatment level of
subsurface nitrogen loss controls: maintained 2003-06
conservation treatment levels, at 23 and 24 percent of
cropped acres; and
 Acres receiving a low treatment level of subsurface
nitrogen loss controls: maintained 2003-06
conservation treatment levels, at 14 and 12 percent of
cropped acres.

60

Table 4.5. Estimation of under-treated acres for sediment loss due to water erosion in the Chesapeake Bay region,
2003-06 baseline condition and 2011 conservation condition.
Soil runoff potential
I. 2003-06 Estimated cropped acres
Low
Moderate
Moderately high
High
All
Percent of Total

Conservation treatment levels for water erosion control
Low
Moderate
Mod-High
High
799,009
204,474
268,264
319,046
1,590,793
37%

954,338
223,051
403,203
495,226
2,075,818
49%

221,865
59,635
127,054
130,583
539,138
13%

17,201
8,861
13,618
34,470
74,151
2%

All
1,992,414
496,021
812,140
979,325
4,279,900
100%

II. 2003-06 Percent of acres in baseline conservation condition with annual average sediment loss less than 2 tons/acre
Low
62
88
78
100
Moderate
37
84
62
100
Moderately High
32
59
69
100
High
6
37
38
63
All
43
69
65
83

77
62
52
28
59

III. 2003-06 Estimate of under-treated acres
Low
Moderate
Moderately High
High
All

0
204,474
268,264
319,046
791,784

0
0
403,203
495,226
898,429

0
0
0
130,583
130,583

0
0
0
0
0

0
204,474
671,467
944,855
1,820,796

IV. 2011 Estimated cropped acres
Low
Moderate
Moderately high
High
All
Percent of Total

267,400
82,100
91,000
121,800
562,300
13%

713,400
291,400
288,500
354,100
1,647,400
38%

524,100
241,300
332,800
349,400
1,447,600
34%

309,800
75,200
92,000
219,100
696,100
16%

1,814,700
690,000
804,300
1,044,400
4,353,400
100%

V. 2011 Percent of acres in current conservation condition with annual average sediment loss less than 2 tons/acre
Low
77
93
98
96
Moderate
34
83
91
100
Moderately high
44
82
93
100
High
11
57
81
87
All
51
82
92
94
VI. 2011 Estimate of under-treated acres
Low
Moderate
Moderately high
High
All

0
82,100
91,000
121,800
294,900

0
0
0
354,100
354,100

0
0
0
0
0

0
0
0
0
0

93
82
85
66
83
0
82,100
91,000
475,900
649,000

Note: Color-shaded cells indicate under-treated acres. Bright yellow-shaded cells indicate groups of acres in which more than 30 percent of the acres
have losses exceeding acceptable levels and were defined as moderate needs acres. Darker yellow-shaded cells indicate high needs under-treated
acres, which were defined as groups of acres in which more than 60 percent of the acres have losses in excess of acceptable levels.
Note: Percent reductions were calculated prior to rounding the values for reporting in the table and the associated text. Percents may not add to totals
because of rounding.

61

Table 4.6. Estimation of under-treated acres for nitrogen loss due to surface runoff in the Chesapeake Bay region,
2003-06 baseline condition and 2011 conservation condition.
Soil runoff potential

Conservation treatment levels for nitrogen runoff control
Low
Moderate
Mod-High
High

I. 2003-06 Estimated cropped acres
Low
Moderate
Moderately high
High
All
Percent of Total

208,143
51,509
99,010
109,317
467,979
11%

741,688
187,142
265,455
354,150
1,548,435
36%

904,986
201,473
386,254
413,920
1,906,632
44%

137,597
55,897
61,421
101,939
356,854
8%

All
1,992,414
496,021
812,140
979,325
4,279,900
100%

II. 2003-06 Percent of acres in baseline conservation condition with annual average nitrogen loss less than 15 lbs/acre
Low
68
79
90
99
Moderate
73
38
81
93
Moderately High
18
43
69
65
High
5
24
32
46
All
43
55
72
77

84
65
56
28
63

III. 2003-06 Estimate of under-treated acres
Low
Moderate
Moderately High
High
All

0
0
99,010
109,317
208,327

0
187,142
265,455
354,150
806,747

0
0
0
413,920
413,920

0
0
0
101,939
101,939

0
187,142
364,465
979,325
1,530,932

IV. 2011 Estimated cropped acres
Low
Moderate
Moderately high
High
All
Percent of Total

93,500
16,900
26,100
67,200
203,700
5%

389,500
131,800
164,800
226,300
912,400
21%

664,900
315,400
328,800
414,300
1,723,400
40%

666,800
225,900
284,600
336,600
1,513,900
35%

1,814,700
690,000
804,300
1,044,400
4,353,400
100%

V. 2011 Percent of acres in current conservation condition with annual average nitrogen loss less than 15 lbs/acre
Low
59
97
94
97
Moderate
*
63
80
88
Moderately high
7
52
97
91
High
13
52
64
79
All
40
73
85
90
VI. 2011 Estimate of under-treated acres
Low
Moderate
Moderately high
High
All

93,500
*
26,100
67,200
186,800

0
0
164,800
226,300
391,100

0
0
0
0
0

0
0
0
0
0

94
79
83
63
82
93,500
0
190,900
293,500
577,900

Note: Color-shaded cells indicate under-treated acres. Bright yellow-shaded cells indicate groups of acres in which more than 30 percent of the acres
have losses exceeding acceptable levels and were defined as moderate needs acres. Darker yellow-shaded cells indicate high needs under-treated
acres, which were defined as groups of acres in which more than 60 percent of the acres have losses in excess of acceptable levels.
Note: Percent reductions were calculated prior to rounding the values for reporting in the table and the associated text. Percents may not add to totals
because of rounding.

62

Table 4.7. Estimation of under-treated acres for nitrogen loss due to subsurface flow and leaching in the Chesapeake
Bay region, 2003-06 baseline condition and 2011 conservation condition.
Soil leaching potential
I. 2003-06 Estimated cropped acres
Low
Moderate
Moderately high
High
All
Percent of Total

Low
64,940
311,527
203,854
50,358
630,678
15%

Conservation treatment levels for
subsurface nitrogen loss control
Moderate
Mod-High
82,214
480,004
220,431
218,012
1,000,661
23%

114,084
1,018,873
695,473
333,166
2,161,597
50%

High

All

13,801
227,855
129,409
115,899
486,964
11%

275,040
2,038,260
1,249,166
717,434
4,279,900
100%

II. 2003-06 Percent of acres in baseline conservation condition with annual average nitrogen loss less than 25 lbs/acre
Low
59
71
92
100
78
Moderate
34
69
81
86
72
Moderately High
21
58
83
100
71
High
53
51
69
100
67
All
34
63
81
93
71
III. 2003-06 Estimate of under-treated acres
Low
Moderate
Moderately High
High
All

64,940
311,527
203,854
50,358
630,678

0
0
220,431
218,012
438,442

0
0
0
0
0

0
0
0
0
0

64,940
311,527
424,285
268,369
1,069,121

IV. 2011 Estimated cropped acres
Low
Moderate
Moderately high
High
All
Percent of Total

4,800
295,600
87,300
115,100
502,800
12%

85,500
676,400
113,400
174,300
1,049,600
25%

103,600
1,270,900
420,900
186,400
1,981,800
46%

75,900
484,000
130,400
128,900
819,200
19%

269,800
2,726,900
752,000
604,700
4,353,400
100%

V. 2011 Percent of acres in current conservation condition with annual average nitrogen loss less than 25 lbs/acre
Low
*
48
92
80
Moderate
56
59
78
76
Moderately high
40
51
87
87
High
50
54
71
92
All
52
57
80
81
VI. 2011 Estimate of under-treated acres
Low
Moderate
Moderately high
High
All

*
295,600
87,300
115,100
498,000

85,500
676,400
113,400
174,300
1,049,600

0
0
0
0
0

0
0
0
0
0

74
71
76
66
71
85,500
972,000
200,700
289,400
1,547,600

Note: Color-shaded cells indicate under-treated acres. Bright yellow-shaded cells indicate groups of acres in which more than 30 percent of the acres
have losses exceeding acceptable levels and were defined as moderate needs acres. Darker yellow-shaded cells indicate high needs under-treated
acres, which were defined as groups of acres in which more than 60 percent of the acres have losses in excess of acceptable levels.
Note: Percent reductions were calculated prior to rounding the values for reporting in the table and the associated text. Percents may not add to totals
because of rounding.

63

These results suggest that less progress was made in terms of
advancing treatment for preventing nitrogen losses in
subsurface flows. Accomplishing a reduction in surface losses
necessarily increases the potential for subsurface losses
because water and nutrients are kept on the farm field, where
they may be lost to subsurface flow pathways. Opportunities
for conservation gains related to subsurface nitrogen losses
remain, particularly in light of the numerous conservation
practices adopted to reduce surface losses.

Phosphorus Losses
Model simulations demonstrated the following changes in
conservation treatment levels for phosphorus losses via
surface runoff pathways on cropped acres in the Chesapeake
Bay region in the 2003-06 baseline condition and 2011
conservation condition (fig. 4.4 and table 4.8):
 Acres receiving a high treatment level of phosphorus
loss controls: 18 percentage point increase, from 20 to
38 percent of cropped acres;
 Acres receiving a moderately high treatment level of
phosphorus loss controls: maintained 2003-06
conservation treatment levels, at 41 and 36 percent of
cropped acres;
 Acres receiving a moderate treatment level of
phosphorus loss controls: 7 percentage point decline,
decreased from 23 to 16 percent of cropped acres; and
 Acres receiving a low treatment level of phosphorus
loss controls: maintained 2003-06 conservation
treatment levels, at 15 and 10 percent of cropped acres.

Treatment Level Criteria
Criteria for water erosion control treatment levels were
derived using the sediment scoring system (Appendix F),
where the relative ability of each practice to avoid, control,
and trap sediment losses is rated for each of the preceding
mitigation categories. Each practice has a maximum of 20
points for each mitigation category, for a total of 60 points.
Each practice occurring at a survey point is scored and
summed for the total points for that conservation system. The
categorization of treatment levels for erosion control is as
follows:
 High treatment: Sum of scores is equal to or greater
than 100;
 Moderately high treatment: Sum of scores is equal to
or greater than 70;
 Moderate treatment: Sum of scores is equal to or
greater than 40; and
 Low treatment: Sum of scores is less than 40.
Criteria for nitrogen runoff treatment levels were derived from
an equal combination of the scores for sediment control
(Appendix F) and the nitrogen application scores (fig. 2.3) to
produce a nitrogen runoff management score. The sediment
control scores are normalized to match the scale of the
potential points for nitrogen applications. Crop residue
classification for the rotation is also used to define the

treatment level for nitrogen runoff. The categorization of
treatment levels for nitrogen runoff control is as follows:
 High treatment: Acres with a nitrogen runoff
management score greater than 65 or a score greater
than 50 with a moderate residue rotation score (>1);
 Moderately high treatment: Acres with a nitrogen
runoff management score greater than or equal to 50 or
a score greater than or equal to 40 with a moderate
residue rotation score (>1);
 Moderate treatment: Acres with a nitrogen runoff
management score greater than or equal to 30; and
 Low treatment: Acres with a nitrogen runoff
management score less than 30.
Criteria for nitrogen treatment levels for leaching are based on
the nitrogen application scores (fig. 2.3) and the rotation’s
crop residue classification (fig. 2.2). The categorization of
treatment levels for nitrogen subsurface loss control is as
follows:
 High treatment: Acres with a nitrogen application
score greater than 45 or a score greater than 30 with a
high residue rotation score (>3);
 Moderately high treatment: Acres with a nitrogen
application score greater than 30 and at least a
moderate residue rotation or a score greater than 20 and
a high residue rotation score (>3);
 Moderate treatment: Acres with a nitrogen application
score greater than 20 and at least a moderate residue
rotation score (>1); and
 Low treatment: Acres with a nitrogen application score
less than or equal to 20 and all other cases not
accounted for in the above criteria. These are typically
low residue rotations with nitrogen application scores
less than or equal to 30.
Criteria for phosphorus runoff treatment levels were derived
from an equal combination of the scores for sediment control
(Appendix F) and the phosphorus application scores (fig. 2.5)
to produce a phosphorus runoff management score. The
sediment control scores are normalized to the match the scale
of the potential points for phosphorus applications. Crop
residue classification for the rotation is also used to define the
treatment level for phosphorus runoff. The categorization of
treatment levels for phosphorus runoff control is as follows:
 High treatment: Acres with a phosphorus runoff
management score greater than 65 or a score greater
than 50 with a moderate residue rotation score (>1);
 Moderately high treatment: Acres with a phosphorus
runoff management score greater than or equal to 50 or
a score greater than or equal to 40 with a moderate
residue rotation score (>1);
 Moderate treatment: Acres with a phosphorus runoff
management score greater than or equal to 30; and
 Low treatment: Acres with a phosphorus runoff
management score less than 30.

64

Table 4.8. Estimation of under-treated acres for phosphorus loss due to surface runoff in the Chesapeake Bay region,
2003-06 baseline condition and 2011 conservation condition.
Soil runoff potential
I. 2003-06 Estimated cropped acres
Low
Moderate
Moderately high
High
All
Percent of Total

Low
222,493
99,683
135,212
212,395
669,783
15%

Conservation treatment levels for
phosphorus runoff control
Moderate
Mod-High
667,221
156,847
290,999
295,932
1,410,999
33%

613,357
153,334
264,243
316,374
1,347,308
31%

High

All

489,343
86,157
121,686
154,623
851,810
20%

1,992,414
496,021
812,140
979,325
4,279,900
100%

II. 2003-06 Percent of acres in baseline conservation condition with annual average phosphorus loss less than 3 lbs/acre
Low
66
79
94
100
Moderate
71
45
76
89
Moderately High
35
48
71
99
High
14
25
53
60
All
44
57
78
91
III. 2003-06 Estimate of under-treated acres
Low
Moderate
Moderately High
High
All
IV. 2011 Estimated cropped acres
Low
Moderate
Moderately high
High
All
Percent of Total

0
135,212
212,395
347,607

0
156,847
290,999
295,932
743,778

0
0
0
316,374
316,374

0
0
0
0
0

0
156,847
426,211
824,702
1,407,760

177,100
62,800
67,900
148,000
455,800
10%

262,600
111,500
139,200
159,000
672,300
15%

634,000
251,500
310,700
363,300
1,559,500
36%

741,000
264,200
286,500
374,100
1,665,800
38%

1,814,700
690,000
804,300
1,044,400
4,353,400
100%

V. 2011 Percent of acres in current conservation condition with annual average phosphorus loss less than 3 lbs/acre
Low
71
97
95
99
Moderate
72
74
84
92
Moderately high
54
59
89
91
High
35
59
70
89
All
57
76
86
94
VI. 2011 Estimate of under-treated acres
Low
Moderate
Moderately high
High
All

87
68
61
37
69

0
0
67,900
148,000
215,900

0
0
139,200
159,000
298,200

0
0
0
0
0

0
0
0
0
0

94
85
82
70
85
0
0
207,100
307,000
514,100

Note: Color-shaded cells indicate under-treated acres. Bright yellow-shaded cells indicate groups of acres in which more than 30 percent of the acres
have losses exceeding acceptable levels and were defined as moderate needs acres. Darker yellow-shaded cells indicate high needs under-treated
acres, which were defined as groups of acres in which more than 60 percent of the acres have losses in excess of acceptable levels.
Note: Percent reductions were calculated prior to rounding the values for reporting in the table and the associated text. Percents may not add to totals
because of rounding.

65

Inherent Vulnerability Factors
The same level of conservation treatment will not yield
identical conservation benefits on all acres due to site
differences, including variability of inherent vulnerabilities
due to soils and climate. Inherent vulnerability factors are
immutable, but conservation practices can prevent or mitigate
the impacts of these vulnerabilities on natural resource
sustainability and water quality. Inherent vulnerability factors
affecting surface runoff potential include soil properties that
promote surface water runoff and erosion—soil hydrologic
group, slope, and K-factor. Inherent factors affecting leaching
potential for loss of nutrients via subsurface flow include soil
properties that promote permeability and/or infiltration—soil
hydrologic group, slope, K-factor, wetness periods, and coarse
fragment content of the soil.
Soil runoff potential and leaching potential were estimated for
each sample point on the basis of vulnerability criteria. A single
set of criteria was developed for all regions and soils in the
United States to allow for regional comparisons. Thus, some soil
runoff and leaching potentials are not well represented in every
region. The criteria were not designed to enable comparisons at
the within-region scale.
Relative to the previous USDA NRCS CEAP report on the
region, this report uses improved soils data (USDA NRCS
2011). Criteria for soil runoff and soil leaching potentials are
presented in Appendix G and H. Figures 4.5 and 4.6 show the
spatial distribution of inherent vulnerability potentials to runoff
and leaching for all soils and land uses in the region. The
inherent runoff and leaching potentials for cropped acres were
used to assess conservation treatment needs.
Cropped acres in the Chesapeake Bay region have a mix of
vulnerability levels relative to potential soil and nutrient losses
via surface runoff loss pathways. Highly erodible lands (HEL)
tend to be more vulnerable to runoff losses than do non-highly
erodible lands (NHEL). Under 2011 conservation conditions:
 23 percent of cropped acres have a high soil runoff
potential;
 19 percent of cropped acres have a moderately high
soil runoff potential;
 12 percent of cropped acres have a moderate soil
runoff potential; and
 47 percent, of cropped acres have a low soil runoff
potential.
Compared to variability in runoff vulnerability, cropped acres
in the region have a relatively consistent need for conservation
treatments to address nitrogen leaching. Though nearly half of
the acres have low vulnerability to soil runoff, only 6 percent
have low vulnerability to leaching. Nitrogen leaching
vulnerability is not correlated with erodibility. Approximately
7 percent of cropped acres in the region have the unique
combination of high vulnerability to leaching and HEL
classification. These soils are generally found on sloping soils
in the Susquehanna Valley and tend to be shallow with more
than 10 percent rock fragments in the surface. Under 2011
conservation conditions:

 17 percent of cropped acres have a high soil leaching
potential;
 29 percent of cropped acres have a moderately high
soil leaching potential;
 48 percent of cropped acres have a moderate soil
leaching potential; and
 6 percent of cropped acres have a low soil leaching
potential.

Estimation of Remaining Conservation
Treatment Needs
Treatment needs were evaluated by using a “matrix approach”
to contrast the conservation treatment level of each acre with
its own inherent vulnerability potential for runoff and/or
leaching. Application of the matrix approach classified
cropped acres into 16 groups—4 classes of soil inherent
vulnerability potentials by 4 conservation treatment levels. In
this way, the matrix approach identified acres on which the
level of conservation treatment was inadequate relative to the
inherent conservation need. This matrix approach may be used
to inform a targeted approach to natural resources
management, as it enables identification of the most probable
combinations of inherent vulnerability potentials and
conservation treatment levels in need of further treatment and
also indicates how critical that need may be. Thus, the matrix
approach is a useful tool for field offices and programs to
better focus resources toward acres with low conservation
treatment levels and high inherent vulnerability potentials to
better address conservation needs.
Relative to lower conservation treatment levels, high or
moderately high treatment levels tend to be far more effective
at reducing losses for all classes of inherent vulnerability
potential, as shown in tables 4.1 through 4.4. Inadequately
treated acres are referred to as “under-treated acres.” By
segregating acres with high loss potential from acres with low
loss potential, the matrix approach provides an estimate of the
acres with the greatest conservation treatment needs. Using
this approach, each category is within 4 percent of the
estimated acres needing treatment for the NRCS-identified
threshold for that resource concern (tables 4.5 through 4.8).
As expected, simulated estimates of sediment and nutrient loss
exhibited a trend of decreasing loss with increasing conservation
treatment level within a given inherent vulnerability potential
class. The highest losses were predicted for groups of acres
where the conservation treatment level was one step or more
below the soil leaching or runoff potential class.
The evaluation of conservation treatment needs was conducted
by identifying which of the 16 groups of acres were
inadequately treated with respect to inherent soil runoff or soil
leaching potential. Three levels of conservation treatment need
were identified and applied to the matrices (tables 4.5 through
4.8):
 High needs acres: the most vulnerable of the undertreated acres, with the least conservation treatment and
the highest losses of sediment and/or nutrients. Groups
of acres in which more than 60 percent of the acres
have losses in excess of acceptable levels were

66

designated as having a high level of conservation
treatment need, indicated by the darkest shading in the
cells in the matrices;
 Moderate needs acres: under-treated acres that
generally have lower levels of vulnerability and/or
have more conservation practices in place than do high
needs acres. The treatment level required to adequately
treat these acres is not necessarily less than what is
required on high needs acres, although it can be. The
sediment and/or nutrient losses are lower on these acres
than on high needs acres and thus there is less potential
on a per-acre basis for reducing sediment and nutrient
loadings with additional conservation treatment. Acres
with a moderate level of conservation treatment needs
are indicated by the lighter shading in the cells in the
matrices; and
 Low needs acres: acres that are adequately treated with
respect to their level of inherent vulnerability. While
gains can be obtained by adding conservation practices
to some of these acres, current losses are small and
additional conservation treatment would reduce field
losses by only a small amount. Groups of acres with
less than 30 percent of the acres exceeding acceptable
levels were defined as adequately treated acres and
designated as having a low level of conservation
treatment need. These cells are not shaded in the
matrices.
The matrices III and VI in each of the tables 4.5 through 4.8
identify conservation treatment needs. Specific criteria were
used to identify the groups of acres that fall into each of the
three levels of conservation treatment need. Criteria were not
tailored to a specific region, but were derived for use in all
regions of the country to allow for comparisons of adequacy
of treatment and identification of under-treated acres across
regions using a consistent analytical framework. The criteria
and steps in the process are as follows.
The percent of acres that exceeded a given level of nutrient or
sediment loss was estimated for each cell in the matrix as a
guide to determine the extent of losses (tables 4.5 through
4.8). These thresholds are referred to as “acceptable levels.”
Losses above these levels were considered unacceptable levels
of loss. Acres with losses above these thresholds were
considered to be in need of further treatment. “Acceptable
levels” for field-level losses used in this study are an annual
average of:
 2 tons per acre for sediment loss;
 15 pounds per acre for nitrogen loss with surface runoff
(soluble and sediment attached);
 25 pounds per acre for nitrogen loss in subsurface flow;
and
 3 pounds per acre for phosphorus loss to surface water
(soluble and sediment-attached).

The threshold for acceptable per acre phosphorus loss was
lowered from 4 to 3 pounds for this report. A 4-pound
threshold was used in the original USDA NRCS CEAP report
for the Chesapeake Bay region (USDA NRCS 2011). The
increase in manure usage and the persistence of phosphorus in
previously eroded sediments necessitates this lower
phosphorus loss threshold to further reduce loads to the Bay.
Under-treated acres—those groups of acres with either a high
or moderate level of conservation treatment need—are shown
in the last matrix in each table (tables 4.5 through 4.8). In most
cases, under-treated acres consisted of acres where the
conservation treatment level was one step or more below the
soil leaching or runoff potential class.
Acceptable levels were initially derived through a series of
forums held at professional meetings of researchers working
on fate and transport of sediment and nutrients in agriculture.
Those meetings produced a range of estimates for edge-offield sediment loss, nitrogen loss, and phosphorus loss,
representing what could realistically be achieved with today’s
production and conservation technologies. The range was
narrowed by further examination of APEX model output,
which also showed that the levels selected were agronomically
feasible in all agricultural regions of the country. In the
Chesapeake Bay region, for example, cropped acres that, with
adequate levels of conservation treatment (including structural
practices and nutrient management), could attain these
acceptable levels are:
 99 percent of cropped acres for sediment loss;
 99 percent of cropped acres for nitrogen loss with
surface runoff;
 88 percent of cropped acres for nitrogen loss in
subsurface flow pathways; and
 91 percent of cropped acres for phosphorus loss to
surface water.

The criteria used to identify acres that need additional
treatment, including those with currently acceptable levels,
are not intended to provide adequate protection for water
quality, although in some environmental settings they may be
suitable for that purpose. Evaluation of how much additional
conservation treatment is needed to meet Federal, State,
and/or local water quality goals in the region is beyond the
scope of this study.

67

Figure 4.5. Soil runoff potential vulnerability classes for soils in the Chesapeake Bay region.

Note: The soil runoff vulnerability potential shown in this map was derived using the criteria presented in Appendix G applied to soil
characteristics for SSURGO polygons. All soils and land uses are represented.

68

Figure 4.6. Soil leaching potential vulnerability classes for soils in the Chesapeake Bay region.

Note: The soil leaching potential classes shown in this map were derived using the criteria presented in Appendix H applied to soil
characteristics for SSURGO polygons. All soils and land uses are represented.

69

Changes in Conservation Treatments and
Treatment Needs, by Resource Concern
The decline in the number of acres with high treatment needs
between 2003-06 and 2011 was largely due to widespread
adoption of structural practices, reduced tillage, and cover
crops, all designed with a primary goal of reducing runoff.
Improvements due to nutrient application management
generally benefitted acreage managed at low conservation
treatment levels.
APEX simulations revealed the following trends in treatment
needs per each resource concern in the Chesapeake Bay region
in the 2003-06 baseline condition and 2011 conservation
condition (table 4.9):

cropped acres are under-treated for only one of the four
resource concerns, most commonly nitrogen leaching, for
which roughly 28 percent of cropped acres are under-treated.
Eight percent of cropped acres are under-treated only for
phosphorus runoff. On acres requiring treatment to address
more than one resource concern, nitrogen runoff and
phosphorus runoff were the most frequently occurring
combination of resource concerns, representing 15 percent of
cropped acres in the region. About 12 percent of cropped acres
were determined to be under-treated for all four resource
concerns.
Table 4.9. Percent of acres with high, moderate, and
low treatment needs.
Sediment Loss Treatment Needs:

Sediment loss:
 High conservation treatment needs acres: maintained
2003-06 conservation levels, at 7 and 3 percent of
acres;
 Moderate conservation treatment needs acres:
decreased by 23 percentage points, from 35 to 12
percent of acres; and
 Low conservation treatment needs acres: increased by
28 percentage points, from 57 to 85 percent of acres.
Nitrogen loss in surface flow:
 High conservation treatment needs acres: decreased by
11 percentage points, from 13 to 2 percent of acres;
 Moderate conservation treatment needs acres:
decreased by 10 percentage points, from 22 to 12
percent of acres; and
 Low conservation treatment needs acres: increased by
21 percentage points, from 65 to 86 percent of acres.
Nitrogen loss in subsurface flow:
 High conservation treatment needs acres: maintained
2003-06 conservation levels, at 5 and <1 percent of
acres;
 Moderate conservation needs acres: increased by 16
percentage points, from 20 to 36 percent of acres; and
 Low conservation treatment needs acres: decreased by
11 percentage points, from 75 to 64 percent of acres.
Phosphorus loss in surface flow:
 High conservation treatment needs acres: maintained
2003-06 conservation levels, at 5 and <1 percent of
acres;
 Moderate conservation treatment needs acres:
decreased by 13 percentage points, from 25 to 12
percent of acres; and
 Low conservation treatment needs acres: decreased by
18 percentage points, from 70 to 88 percent of acres.
Overall, acreage with high conservation treatment needs for
one or more resource concern was improved by 15 percentage
points, such that cropped acres with a high need for one or
more resource concern declined from 19 to 4 percent of
cropped acres between 2003-06 and 2011. About 46 percent of

2003-06
2011
Change

Low
57%
85%
28%

Moderate
35%
12%
-23%

High
7%
3%
-4%

Nitrogen Surface Runoff Treatment Needs:
2003-06
2011
Change

Low
65%
86%
21%

Moderate
22%
12%
-10%

High
13%
2%
-11%

Nitrogen in Subsurface Flow Pathways:
2003-06
2011
Change

Low
75%
64%
-11%

Moderate
20%
36%
16%

High
5%
<1%
-5%

Moderate
25%
12%
-13%

High
5%
<1%
-5%

Phosphorus in Surface Runoff:
2003-06
2011
Change

Low
70%
88%
18%

Treatment Needs for One or More Resource Concern:
2003-06
2011
Change

Low
41%
54%
13%

Moderate
40%
42%
2%

High
19%
4%
-15%

Note: may not total to 100 percent due to rounding.

The most critical conservation need in the region is the need
for complete and consistently applied nutrient application
management following the 4Rs: appropriate rate, timing,
method, and form of nitrogen and phosphorus application.
Cropped acres with a high need to control nitrogen and/or
phosphorus losses in surface runoff were largely addressed,
such that they were reduced from 18 to 2 percent of cropped
acres in the region. However, many of these gains were made
via structural practice, tillage management, and cover crop

70

adoption, all of which support the control and trap aspects of
an ACT conservation approach. There is still opportunity to
address the avoid component of ACT through better nutrient
application management adhering to the 4Rs. About 40
percent of cropped acres in the region have a high or
moderate need for additional nutrient management for
nitrogen and/or phosphorus (table 4.9).

Conservation treatment needs for one or more
resource concern
As just discussed, approximately 2 million cultivated cropland
acres (46 percent) require additional conservation treatment
for only one of the four resource concerns, while other acres
require additional treatment for two or more resource
concerns. Simulations accounting for acres with treatment
needs for multiple resource concerns determined that
conservation practices adopted in the 2003-06 baseline
condition and 2011 conservation condition achieved the
following on acres needing treatment for more than one
resource concern (fig. 4.7 and tables 4.9 and 4.10):
 High treatment needs acres: decreased by 15
percentage points, from 19 percent (813,000 acres) to 4
percent (157,000 acres) of the region’s cultivated
cropland;
 Moderate treatment needs acres: maintained 2003-06
conservation levels at 40 and 43 percent of acres in
2003-06 and 2011; and
 Low conservation needs acres: increased by 13
percentage points, from 41 percent (1,754,390 acres) to
54 percent (2,334,400 acres) of the region’s cultivated
cropland.
High Conservation Treatment Needs Acres: Acres with a
high level of need for conservation treatment are typically the
most vulnerable of the under-treated acres, have the least
conservation treatment in place, and suffer the highest losses
of sediment and/or nutrients. Ninety-three percent of these
acres have losses higher than the acceptable level criteria used
in the matrix approach for either sediment or nutrients (tables
4.5 to 4.8). Under the 2011 conservation condition these acres
lost (per acre per year, on average):
 12.7 tons of sediment;
 31 pounds of nitrogen with surface runoff;
 41 pounds of nitrogen in subsurface flow; and
 7.9 pounds of phosphorus.
Because losses are high on these acres, acres with a high level
of treatment need have the greatest potential for reducing
agriculturally derived sediment and nutrient loadings with
additional conservation treatment.

and tons, there is less potential on a per-acre basis for reducing
nutrient and sediment losses with additional conservation
treatments. Seventy percent of these acres have losses higher
than the acceptable level criteria used in the matrix approach
for either sediment or nutrients (tables 4.5 to 4.8). In 2011
these acres lost (per acre per year, on average):
 3.6 tons of sediment;
 14 pounds of nitrogen with surface runoff;
 29 pounds of nitrogen in subsurface flows; and
 2.9 pounds of phosphorus.
While the potential benefits of additional treatment on
moderate conservation treatment needs acres are less than
they are for high conservation treatment needs acres, a
portion of these acres may need to be treated to meet water
quality goals in the region. Evaluation of conservation
treatment needed to meet water quality goals in the region is
beyond the scope of this study.
Low Conservation Treatment Needs Acres: Acres with a low
level of need for conservation treatment consist of acres that
are adequately treated with respect to the level of inherent
vulnerability. Only 16 percent of these acres have losses
higher than the acceptable level criteria used in the matrix
approach, almost all of which are for a single resource concern
(tables 4.5 to 4.8). In 2011 these acres lost (per acre per year,
on average):
 1.1 tons of sediment;
 7 pounds of nitrogen with surface runoff;
 17 pounds of nitrogen in subsurface flows; and
 1.2 pounds of phosphorus.
While gains can be obtained by adopting additional
conservation practices on some of these acres, because losses
are small, additional conservation treatment would reduce
field losses by only a small amount.
It should also be noted that continued conservation planning
and management is necessary to keep acreage adequately
treated and in this low conservation treatment needs category.
Most, if not all, conservation practices require annual or semiannual maintenance or annual application. In particular, the
full benefits of sound nutrient management are only accrued if
the management is consistently applied to every crop grown
on a given acre. Acreage currently in this low needs category
is receiving adequate treatments to meet conservation needs.
Were these treatments removed, these acres would likely be
re-categorized as moderate or high conservation treatment
needs acres due to the increased nutrient and sediment losses
that would accompany conservation practice abandonment.

Moderate Conservation Treatment Needs Acres: Acres with a
moderate level of need for conservation treatment consist of
under-treated acres that generally have lower levels of
vulnerability and/or have more conservation practices in place
than do acres with a high level of need. The sediment and/or
nutrient losses tend to be lower than they are on acres with
high conservation treatment needs and thus in terms of pounds

71

Figure 4.7. Percent of cropped acres with a high, moderate, or low level of need for additional conservation treatment for one or more
resource concern in the Chesapeake Bay region, 2003-06 baseline condition and 2011 conservation condition.
60%
Percent of Cropped Acres

50%
40%
30%
20%
10%
0%

Low Treament Needs

Moderate Treatment Needs

High Treatment Needs

2003-06

41%

40%

19%

2011

54%

43%

4%

Table 4.10. Under-treated acres for the four sub-regions in the Chesapeake Bay region, 2003-06 baseline condition and 2011
conservation condition.

Subregion
Code

Sub-region
name

0205

Susquehanna
River

Data
Year
200306
2011

0206

Upper
Chesapeake
Bay

0207

0208

Percent of
cropped
acres in
Chesapeake
Bay region

High Treatment Need acres
Percent of
acres in
Percent of
Chesapeake
acres in
Acres
Bay region
subregion

All Under-Treated acres
Percent of
acres in
Percent of
Chesapeake
acres in
Acres
Bay region
subregion

41
46

585,833
150,800

14
4

34
8

1,297,467
1,047,500

30
24

75
52

200306
2011

28
23

45,621
0

1
0

4
0

504,579
399,200

12
9

42
39

Potomac River

200306
2011

16
17

140,251
4,200

3
<1

21
1

476,953
355,900

11
8

70
49

Lower
Chesapeake
Bay

200306
2011

16
14

41,117
1,700

1
<1

6
<1

237,716
216,400

6
5

35
36

812,823
156,700

19
4

100
100

2,516,715
2,019,000

59
46

100
100

200306
100
Total
2011
100
Note: Percents may not add to totals because of rounding.

72

Chapter 5
Offsite Water Quality Effects of
Conservation Practices
The Soil and Water Assessment Tool—SWAT
Offsite estimates of water quality benefits were assessed using
the Soil and Water Assessment Tool (SWAT) and inputs from
a number of databases required to run SWAT at the watershed
scale (Arnold et al. 1999; Srinivasan et al. 1998). SWAT is
capable of simulating the transport of water, sediment,
pesticides, and nutrients from the land to receiving streams,
routing the flow downstream to the next watershed, and
ultimately simulating delivery to estuaries, bays, and oceans
(fig. 5.1).
Figure 5.1. Sources of water flows, sediment, and agricultural
chemicals simulated with SWAT.

The analyses conducted for this report were intended to provide
long-term estimates of benefits associated with adoption of
conservation practices on cultivated cropland. For that reason,
the only land use changed between the two sampling periods is
land use associated with cultivated cropland. In order to
compare the impacts of conservation practices on cultivated
croplands in 2003-06 with the impacts of new and improved
conservation practices in 2011, all other land use loads were
held at the same rate for analyses of both sampling periods.
Therefore, this chapter does not account for any conservation
practice changes made in other land use sectors, including land
in long term conserving cover like CRP.

routing phase (channel processes) simulates the movement of
water, sediment, and nutrients from the outlet of the upstream
watershed through the main channel network to the watershed
outlet.

Upland Processes
The water balance is the driving force for transport and
delivery of sediment and nutrients from fields to streams and
rivers. For this study, upland processes for non-cultivated
cropland were modeled using SWAT, while source loads for
cultivated cropland were estimated with APEX.
In SWAT, each watershed is divided into multiple Hydrologic
Response Units (HRUs) that are simulated as having
homogeneous land use, management, and soil characteristics.
An HRU is not a contiguous land area, but rather represents the
percentage of the watershed that has the characteristics
represented by that HRU. In this study, SWAT was used to
simulate the fate and transport of water, sediment, and nutrients
for the following land use categories, referred to as HRUs:
 Pastureland
 Range shrub
 Range grass
 Urban
 Mixed forest
 Deciduous forest
 Evergreen forest
 Horticultural lands
 Forested wetlands
 Non-forested wetlands
Upland processes were modeled for each of these HRUs in each
watershed (8-digit hydrologic unit code [HUC]) (fig. 5.2). The
model simulates surface runoff from daily rainfall and
irrigation; percolation modeled with a layered storage routing
technique combined with a subsurface flow model; lateral
subsurface flow; groundwater flow to streams from shallow
aquifers; potential evapotranspiration; snowmelt; transmission
losses from streams; and water storage and losses from ponds.
Figure 5.2. SWAT model upland simulation processes.

Like APEX, SWAT is a physical process model with a daily
time step (Arnold and Fohrer 2005; Arnold et al. 1998;
Gassman et al. 2007).11 The hydrologic cycle in the model is
divided into two phases. The land phase (upland processes)
simulates the amount of water, sediment, and nutrients
delivered from the land to the outlet of each watershed. The
11

A complete description of the SWAT model can be found at
http://www.brc.tamus.edu/swat/index.html.

73

Upland processes for cultivated cropland were modeled using
APEXv1307, as described in previous chapters. The cultivated
cropland in long-term conserving cover was held constant at
2003-06 conservation levels and was considered to have the
same impact on instream water quality in both 2003-06 and
2011. The weighted averages of per acre APEX model output
for surface water delivery, sediment, and nutrients was
multiplied by the acres of cultivated cropland and used as
SWAT model inputs to simulate each 8-digit HUC. The
acreage weights for the CEAP sample points were used to
calculate the per-acre loads. Several of the 8-digit HUC
watersheds in each region had too few CEAP sample points to
reliably estimate edge-of-field per-acre loads. In these cases,
the 6-digit HUC per-acre loads and sometimes the 4-digit
HUC per-acre loads were used to represent cultivated
cropland.
Land management activities for permanent hayland, pastureland, and long-term conserving cover were modeled in SWAT.
No management was simulated for rangeland, forestland,
urban land, or horticulture. For permanent hayland, the
following management activities were simulated:
 Three hay cuttings per crop year;
 Hay was fertilized with nitrogen according to the crop
need, as determined by an auto-fertilization routine,
which was set to grow the crop without undue nitrogen
stress;
 For legume hay, phosphorus was applied at the time of
planting every fourth year at a rate of 50 pounds per
acre, followed by applications of 13 pounds per acre
every other year;
 Manure was applied to hayland at rates estimated from
probable land application of manure, using the methods
described in USDA NRCS (2003); and
 For hayland acres which land-use databases indicated
were irrigated, water was applied at a frequency and
rate defined by an auto-irrigation routine in SWAT.
For pastureland, the following management activities were
simulated:
 Grazing, via simulation of four grass cuttings per year;
 Pastureland was fertilized with nitrogen, as determined
by an auto-fertilization routine, which was set to grow
grass without undue nitrogen stress;
 Manure was applied to pastureland at rates estimated
from probable land application of manure, using the
methods described in USDA NRCS (2003); and
 Manure nutrients from grazing animals were simulated
for pastureland according to the density of pastured
livestock as reported in the 2002 Census of
Agriculture. Non-recoverable manure was estimated by
subtracting recoverable manure available for land
application from the total manure nutrients
representing all livestock populations. Non-recoverable
manure nutrients include the non-recoverable portion
from animal feeding operations. Estimates of manure
nutrients were derived from data on livestock
populations as reported in the 2002 Census of
Agriculture, which were available for each 6-digit
HUC and distributed among the 8-digit HUCs on a peracre basis.

Cropped acres could also be converted to long-term
conserving cover, establishment of which consists of planting
suitable native or domestic grasses, forbs, or trees, typically on
environmentally sensitive cultivated cropland. The national
database documenting acreage in long-term conserving cover
was not updated between the publication dates of the previous
and current report (USDA NRCS 2011). Therefore,
simulations reported herein use the same acreage amounts
(100,000 acres) for land in long-term conserving cover for
both 2003-06 and 2011 and there is no change in benefits from
this management practice. It should be noted that conversion
to long-term conserving cover virtually eliminates soil erosion
and sediment losses.
A summary of the total amount of nitrogen and phosphorus
applied to agricultural land in the model simulation, including
nitrogen and phosphorus applied to cultivated cropland in the
APEX model, is presented in table 5.1. Manure nutrients from
wildlife are not included.

Urban Sources
Discharges from industrial and municipal wastewater
treatment plants can be major sources of sediment and
nutrients in some watersheds. For this study, the point source
database developed by the Environmental Protection Agency
(EPA) for use in the Chesapeake Bay model was used for the
period from 1985 through 2011. For the years before 1985, the
annual point source loads of 1985 were used. Point source
loads are aggregated within each watershed and average
annual loads are input into SWAT at the watershed outlet.
Urban runoff is estimated separately for three categories of
cover: 1) impervious surfaces, such as buildings, parking lots,
paved streets, etc.; 2) impervious surfaces hydraulically
connected to drainage systems, such as storm drains; and 3)
impervious surfaces not hydraulically connected to drainage
systems. For estimating surface water runoff, a runoff curve
number of 98 was used for impervious surfaces connected
hydraulically to drainage systems and a composite runoff
curve number was used for impervious surfaces not
hydraulically connected to drainage systems. Sediment and
nutrients carried with storm water runoff to streams and rivers
were estimated using regression equations developed by
Driver and Tasker (1988).
Construction areas were assumed to represent 3 percent of
urban areas. Parameters in the SWAT soil input file were
modified to produce surface runoff and sediment yield that
mimicked the average sediment load from published studies
on construction sites.
Not included in the point source data are: 1) pseudo-point
sources, such as confined animal feeding operations and
fertilizer handling and distribution centers; 2) urban
applications of nutrients and chemicals (lawns, golf-courses,
etc.); or 3) small communities and homes not connected to
sewer systems.

74

Table 5.1. Summary of commercial fertilizer and manure nutrients applied to agricultural land in SWAT (pastureland and hayland)
and APEX (cultivated cropland) model simulations, Chesapeake Bay watershed, 2003-06 baseline condition and 2011 conservation
condition.
Subregion
code

Subregion name

Commercial
nitrogen
fertilizer
(tons/year)

Nitrogen from
manure
(tons/year)

Total
nitrogen
(tons/year)

Commercial
phosphorus
fertilizer
(tons/year)

Phosphorus
from
manure
(tons/year)

Total
phosphorus
(tons/year)

0205
0206
0207
0208

Susquehanna River
Upper Chesapeake Bay
Potomac River
Lower Chesapeake Bay
Total

51,207
37,207
23,683
25,670
137,767

38,243
14,803
12,494
184
65,724

Cultivated Cropland (2003-06)
89,450
10,530
52,009
6,034
36,177
4,650
25,854
5,234
203,491
26,449

14,356
4,557
5,633
94
24,640

24,887
10,592
10,282
5,328
51,089

0205
0206
0207
0208

Susquehanna River
Upper Chesapeake Bay
Potomac River
Lower Chesapeake Bay
Total

59,827
41,173
25,490
24,141
150,632

47,074
12,702
14,401
3,060
77,236

Cultivated Cropland (2011)
106,901
12,734
53,875
5,698
39,891
4,034
27,202
4,509
227,868
26,975

16,568
4,651
5,642
987
27,848

29,303
10,348
9,676
5,495
54,822

0205
0206
0207
0208

Susquehanna River
Upper Chesapeake Bay
Potomac River
Lower Chesapeake Bay
Total

22,681
787
14,913
13,479
51,860

3,196
309
5,136
1,065
9,706

Hayland (2003-06 and 2011)
25,876
2,774
1,096
110
20,049
632
14,544
181
61,566
3,698

1,446
142
2,448
514
4,549

4,220
252
3,080
695
8,247

0205
0206
0207
0208

Susquehanna River
Upper Chesapeake Bay
Potomac River
Lower Chesapeake Bay
Total

8,532
1,880
6,928
3,394
20,734

13,496
4,000
16,362
8,080
41,939

16,646
4,821
19,748
10,008
51,224

Pastureland and Rangeland (2003-06 and 2011)
36,160
44,693
3,150
9,091
10,971
822
33,652
40,580
3,386
14,382
17,777
1,927
93,285
114,020
9,285

Note: Nitrogen and phosphorus applications for Hayland, Pastureland, and Rangeland were held to 2003-06 estimates for analyses of both sampling periods.

Atmospheric Nitrogen Deposition
Atmospheric deposition of nitrogen can be a significant
component of the nitrogen balance. Nitrogen deposition data
(loads and concentrations) were developed from the National
Atmospheric Deposition Program/National Trends Network
database (NADP/NTN 2004). To account for impacts of wet
deposition, when a rainfall event occurred in the model
simulation, the amount of rainfall was multiplied by the
average ammonium and nitrate concentrations calculated for
the watershed. The simulation also added an additional
amount of ammonium and nitrate on a daily basis to account
for dry deposition. Changes in atmospheric nitrogen as a result
of changes in conservation or production practices are not
considered in this report, as these effects are prospective and
not yet available in deposition data.

Figure 5.3. SWAT model channel simulation processes.

Routing and Channel Processes
SWAT simulates stream and channel processes, including
channel flood routing, channel sediment routing, nutrient
routing, and transformations modified from the QUAL2E
model (fig. 5.3). As water flows downstream, some may be
lost to evaporation and transmission through the channel bed.
Another potential loss pathway is removal of water from the
channel for agricultural, rural, or urban use. Flow may be
supplemented by rainfall directly on the channel and/or
addition of water from point source discharges.

75

Source Loads and Instream Loads
All source loads are introduced into SWAT at the outlet of
each watershed (8-digit HUC). Flows and source loads from
upstream watersheds are routed through each downstream
watershed, including reservoirs when present. 12
A sediment delivery ratio was used to account for deposition
in ditches, floodplains, and tributary stream channels during
transit from the edge-of-field to the outlet. The sediment
delivery ratio used in this study is a function of the ratio of the
time of concentration for the HRU (land uses other than
cultivated cropland) or field (cultivated cropland) to the time
of concentration for the watershed (8-digit HUC). The time of
concentration for the watershed is the time from when a
surface water runoff event occurs at the watershed’s point
most distant from the outlet to the time the surface water
runoff reaches the outlet of the watershed. It is calculated by
summing the overland flow time (the time it takes for flow to
move from the remotest point in the watershed to the channel)
and the channel flow time (the time it takes for flow in the
upstream channels to reach the outlet). The time of
concentration for the field is derived from APEX. The time of
concentration for the HRU is derived from characteristics of
the watershed, the HRU, and the proportion of total acres
represented by the HRU. Consequently, each cultivated
cropland sample point has a unique delivery ratio within each
watershed, as does each HRU.13 The sediment delivery ratio
and an enrichment ratio were used to simulate organic
nitrogen and organic phosphorus in ditches, floodplains, and
tributary stream channels during transit from the edge-of-field
to the outlet. The enrichment ratio was defined as the organic
nitrogen and organic phosphorus concentrations from the
edge-of-field divided by their concentrations at the watershed
outlet. As sediment is transported from the edge-of-field to the
watershed outlet, coarse sediments are deposited first while
the fine sediment that holds organic particles remains in
suspension, enriching the organic concentrations delivered to
the watershed outlet.
A separate delivery ratio is used to simulate the transport of
nitrate nitrogen and soluble phosphorus. In general, the
proportion of soluble nutrients delivered to rivers and streams
is higher than the proportion attached to sediments because
they are not subject to sediment deposition.
For reporting purposes, edge-of-field loads and source loads
were aggregated over the 8-digit HUCs to the four subregions
in the region (4-digit HUCs). Figure 5.4 shows the location of
each subregion and the 8-digit HUCs included in each. For the
Susquehanna River and the Potomac River (8-digit HUC
groups I and III), instream loads represent the loads at the
outlet of the subregion. For the Upper Chesapeake (8-digit
HUC group II), the instream loads represent the sum of the
loads at the outlets of 8-digit HUCs draining to into

Chesapeake Bay in subregion 0206. For the Lower
Chesapeake (8-digit HUC groups IV), instream loads
represent the sum of the loads at the outlets of the
Rappahannock, York, and James Rivers in subregion 0208.
For the Lower Chesapeake (8-digit HUC group V), instream
loads represent the load at the outlet of the Lower Eastern 8digit HUC (0208).
There are four points in the modeling process at which source
loads or instream loads are assessed for sediment, shown in
the schematic in figure 5.5.
1. Edge-of-field loads from cultivated cropland—
aggregated APEX model output as reported in the
previous chapter. Edge-of-field loads for the
Chesapeake Bay watershed differ slightly from those
reported in the previous chapter because in the
discussion on the Chesapeake Bay region, two 8-digit
HUCS that drain to the Atlantic and loads from land in
long-term conserving cover were included;
2. Delivery to the watershed outlet from cultivated
cropland—aggregated edge-of-field loads after
application of delivery ratios. Loadings delivered to
streams and rivers differ from the amount leaving the
field because of losses during transport from the field
to the stream. Delivery ratios are used to make this
adjustment;
3. Delivery to the watershed outlet from land uses other
than cultivated cropland as simulated by SWAT, after
application of delivery ratios. Point sources are
included; and
4. Loadings in the stream or river at a given point.
Instream loads include loadings delivered to the
watershed outlet from all sources as well as loads
delivered from upstream watersheds, after accounting
for channel and reservoir processes.
Terminology Used in this Report:
Chesapeake Bay Watershed
Versus
Chesapeake Bay Region
Estimates presented in this chapter exclude two
8-digit watersheds in the Upper Chesapeake Bay
subregion that drain to the Atlantic Ocean (8digit HUCs 02060010 and 02080110). The area
excluding these two subregions is referred to as
the Chesapeake Bay watershed. However, tables
and figures elsewhere in the report include the
cropped acres in these two 8-digit HUCs; the
area that includes these two watersheds is
referred to as the Chesapeake Bay region.

12

For a complete documentation of HUMUS/SWAT as it was used in this
study, see “The HUMUS/SWAT National Water Quality Modeling System”
at http://www.nrcs.usda.gov/technical/nri/ceap.
13

For a complete documentation of delivery ratios used for the Chesapeake
Bay region, see “Delivery Ratios Used in CEAP Cropland Modeling” at
http://www.nrcs.usda.gov/technical/nri/ceap.

76

Figure 5.4. Subregions and 8-digit HUC groups used for reporting of source loads and instream loads for the Chesapeake Bay
watershed.

77

Figure 5.5. Schematic of sediment sources and delivery as modeled with SWAT for the Chesapeake Bay watershed.

Erosion – Detachment,
Sheet and Rill

Hillslope
Deposition
Terraces
Buffers

Leaving edge of field

Leaving HRU

Cultivated
cropland
(APEX)

MUSLE
Sediment
Yield

Other land uses
(SWAT)
Ditches,
Channels,
and Flood
Plains

HUC Outlet
Sediment Yields

Point Sources

Sediment delivery ratio
(Edge of field
HUC Outlet)
Channel &
Floodplain
Deposition

HUC River
Routing (SWAT)
Sediment Transported
from River

Conservation Practice Effects on Water
Quality
The results from the onsite APEX model simulations for
cropped acres, excluding acres of cultivated cropland
classified as land in long-term conserving cover, were
integrated into SWAT to assess the effects of conservation
practices on instream loads of sediment, nitrogen, and
phosphorus. The simulated results for land in long-term
conserving cover were kept constant for the re-analysis of the
2003-06 and the 2011 survey results. The effects of
conservation practices on water quality were assessed by
comparing SWAT model simulation results for the no-practice
scenario, 2003-06 baseline condition, and 2011 conservation
condition. For each scenario, only the management of cropped
acres was changed. All other aspects of the simulations,
including sediment and nutrient loads from point sources and
land uses other than cultivated cropland, remained the same.

When the original USDA NRCS Chesapeake Bay region
report was written (USDA NRCS 2011), the 2001 National
Land Cover Database (NLCD) (Homer et al. 2007) provided
the most timely and robust estimates of non-cultivated
cropland, such as pastureland and permanent hayland, and
non-agricultural land uses, such as forests and urban areas.
The 2001 NLCD, therefore, informed the SWAT modeling of
instream effects estimates in the original report. The modeling
efforts in this report rely on the most recent (2007) NRI
estimates for cultivated acres of cropland values and keep all
other land use estimates consistent with the original
Chesapeake Bay region CEAP report (USDA NRCS 2011),
including land in long-term conserving cover. By holding
these inputs constant, the focus of this report is on the effect of
changing conservation practices on the cropped acres in the
2003-06 baseline condition as compared to the 2011
conservation condition. By holding all other inputs constant,
these differences can be isolated, without confounding effects
from the changes in loads from the other land uses.

78

SWAT accounts for the transport of water, sediment, and
nutrients from the land to receiving streams and routes the
flow downstream to the next watershed and ultimately to
estuaries and oceans. Not all of the water, sediment, and
nutrients that leave farm fields are delivered to streams and
rivers. Water may be lost to deep water storage or evaporation.
Some material is bound up permanently in various parts of the
landscape during transport. In addition, instream degradation
processes may release previously deposited sediment and
nutrients into the instream flow and streambed deposition and
accumulation may remove or trap a portion of the sediment
and/or nutrients after delivery to streams and rivers.
Agricultural conservation practices have been adopted in the
Chesapeake Bay region, with the goal of lowering nitrogen,
phosphorus, and sediment contributions to the Chesapeake
Bay, thus contributing to an improvement of the ecological
health of the Bay. At the field scale, conservation practices
have been linked to measureable effects and tangible benefits.
However, demonstrating conservation practice effects at larger
spatial scales has proven far more challenging. The apparent
dissociation between edge-of-field assessments and watershed
or sub-watershed scale assessments has been attributed to a
number of causes, including legacy sediment and nutrients and
the associated lag-time commonly observed between
conservation adoption and quantifiable large scale results.
Streams, tributaries, and rivers have received sediment and
nutrient inputs throughout their histories. Once introduced into
a waterway, sediment and nutrients may be carried
downstream, or may accumulate at any point along the
pathway from edge-of-field to the Bay. Once sediment and
nutrients have settled out of the flowing water, they become a
part of “legacy” sediment and nutrients. Resuspension and
redistribution may occur days, years, or decades in the future
(McDowell et al. 2002). Delivery of legacy sediment and
nutrients to the estuaries or Bay often masks the impacts of
current and recently applied conservation practices. Legacy
sediment and nutrients are one of the primary reasons that
evaluation of conservation practice success and identification
of remaining challenges in watershed management cannot be
regarded as solely reflective of today’s management (Sharpley
et al. 2013).
There are numerous causes that contribute to reintroduction of
legacy sediment and nutrients into the water. Storms and
flooding may dislodge sediment and nutrients, not only in the
rivers and streams, but also in the Bay itself. Estuaries, of
which Chesapeake Bay is North America’s largest, naturally
accumulate sediments and nutrients. In fact, it is estimated that
the estuaries along the East Coast of the United States have
trapped roughly 90 percent of the sediment their tributaries
have delivered (Meade 1982). This function makes estuaries
vulnerable to large storms, which are often associated with
large discharges of sediment and associated nutrients. For
example, Tropical Storm Agnes (1972) caused the
resuspension and discharge of about 31 million tons of
sediment and associated nutrients into the Chesapeake Bay,
drastically disrupting biological communities in the Bay, some
of which were still not recovered by 2005 (Schubel 1977;
Lynch 2005). In 2011, flooding associated with Tropical

Storm Lee resuspended and flushed 6.7 million tons of
sediments from the Susquehanna River into the Bay, creating
a dense sediment plume across half of Chesapeake Bay
(Cheng et al. 2013). Though less dramatic, the effects of
Tropical Storm Lee may still be impacting sediment and
nutrient quantification in the Bay. As the Chesapeake Bay
region is anticipated to suffer more tropical storm activity in
the future, it will become more important that these weather
events, currently viewed as anomalies, are accounted for when
quantifying nutrient and sediment loads in efforts to analyze
conservation effects.
Additionally, even in the absence of storms and associated
flooding, conservation practices may, themselves contribute to
increased sediment and nutrient dislodging caused by scouring
and channel cutting of streams and rivers. This is because
when practices are successful at removing sediment and
nutrients prior to the water leaving the field (or other source),
and practices are not put in place to attenuate the hydrologic
discharge, the cleaner water has a higher potential to detach
sediment. Flume studies have shown sediment detachment to
decrease by as much as 42 percent with increasing sediment
concentrations in the water; as water saturates with higher
sediment loads, deposition eventually exceeds detachment
(Merten et al. 2001). The erosion of stream and river banks
and beds may release legacy sediment and nutrients deposited
there due to losses from past land uses. The cleaner water may
also cause nutrients bound to the sediment to unbind from the
soil particles and dissolve into the water. These instream
processes may delay quantifiable effects of upland
conservation practices on sediment and nutrient loads
delivered to the Bay.
Legacy nutrients and sediments contribute to lag-times, the
length of which are dictated by the interaction of multiple
factors, including: the time required for the conservation
practice to produce an effect at the field scale; the time it takes
for that effect to be delivered to the watershed or subwatershed; the time it takes for that field-scale benefit to
translate to a watershed or sub-watershed benefit; and the
amount of time it takes for sampling protocol to quantify the
benefit (Meals et al. 2010). Lag-times between conservation
practice adoption and observable impact are well documented
(Sharpley et al. 2013). The University of Maryland Eastern
Shore’s research farm is located on the site of a former poultry
operation, with 30 years of poultry litter application.
Experiments to decrease the phosphorus loads from the soils
did not show a benefit, even at the field-scale, for nearly a
decade (Kleinman et al. 2011). In 2005 Maryland’s governor
declared the Corsica River as the State’s targeted restoration
watershed. A massive effort of private, local, State, and
Federal collaboration led to the adoption of numerous
conservation practices in the river’s watershed, including
installation of buffers, storm water and sewage treatment
upgrades, wetland restoration, and shoreline enhancement.
However, Maryland’s Department of Natural Resources
reports that from 2006 to 2011, the majority of sites in the
watershed showed no change in their biological condition.
Further, observable nutrient reduction occurred in only two of
the Corsica’s non-tidal tributaries (MDNR 2012). An
independent study found that the most pronounced trends

79

occurred after 2010, suggesting that it took 5 years for the
conservation measures to manifest in decreased sediment
deposition in the river (Palinkas 2013). It will likely take
longer for the benefits to be quantifiable in the Bay. A recent
USGS study suggests under current conservation conditions,
total daily nitrogen loads will continue to rise until the year
2050 due to lag-times associated with legacy nitrogen in
groundwater, which may take more than 50 years to flush
through the groundwater system on the Delmarva Peninsula in
the Chesapeake Bay (Sanford and Pope 2013, accepted).
Similarly, all measured instream nutrient and sediment fluxes
collected during each survey period informing this report do
not reflect impacts of conservation practices installed during
the same survey period. If the 5-year lag-time observed in the
Corsica River study were applicable across the region, it is
reasonable to consider the instream, outlet, and Bay nutrient
and sediment loading quantified in 2011 are reflective of
conservation practices in place during the first sampling
period (2003-06). However, Phillips and Lindsey (2003)
suggest that it may take decades for benefits of conservation
practices to have demonstrable impact in the Chesapeake Bay.
Even if the shorter observed lag-times hold true, the benefits
of the widespread conservation practices put in place as a
result of the 2009 Chesapeake Bay Protection and Restoration
Executive Order will likely not be evident in the instream,

outlet, and Bay data collected in the 2011 sampling period and
may not be observable until 2014 or sometime thereafter.

Land Use in the Chesapeake Bay Watershed
The 2001 National Land Cover Database (NLCD) (Homer et
al. 2007) was the principle source of acreage for SWAT
modeling (table 5.2). The 2003 National Resources Inventory
(NRI) was used to adjust NLCD cropland acreage estimates to
include acres enrolled in the Conservation Reserve Program
General Signups, used here to represent cropland currently
maintained in long-term conserving cover. Consequently,
cultivated cropland acres used to simulate the effects of
conservation practices on water quality differ slightly from the
cultivated cropland acres reported in the previous chapters,
which were estimated on the basis of the CEAP Cropland
sample. In addition, estimates presented in this chapter on offsite water quality in the Chesapeake Bay watershed exclude
two 8-digit HUC watersheds in the Upper Chesapeake Bay
subregion that drain to the Atlantic Ocean (8-digit HUCs
02060010 and 02080110). These watersheds were included in
analyses of the Chesapeake Bay region, discussed in previous
chapters.

Table 5.2. Land use in the Chesapeake Bay watershed.
Subregion
code
0205
0206
0207
0208

Subregion name
Susquehanna River
Upper Chesapeake Bay
Potomac River
Lower Chesapeake Bay
Total

Cultivated
cropland
(acres)*
2,007,380
1,218,106
611,355
553,641
4,390,482

Hayland not in
rotation with
crops (acres)
1,314,114
49,817
670,212
451,427
2,485,571

Pasture and
grazing land
not in
rotation with
crops (acres)
1,519,448
812,045
1,565,170
1,381,713
5,278,375

Urban land
(acres)
1,314,783
526,715
1,021,360
734,820
3,597,679

Forest and
other
(acres)**
11,230,468
2,310,880
5,385,808
7,307,893
26,235,048

Total land
(acres)***
17,386,193
4,917,564
9,253,905
10,429,494
41,987,155

Note: Estimates in this table differ from estimates for the Chesapeake Bay region by excluding the two 8-digit HUCs draining into the Atlantic Ocean.
* Acres of cultivated cropland include land in long-term conserving cover as well as hayland and pastureland in rotation with crops from 2003-06 survey.
** Includes forests (all types), wetlands, range brush, horticulture, and barren land.
*** Exclusive of water.

80

Sediment
Simulation results suggest the continued adoption of new and
improved conservation practices aimed at sediment load
reduction on cultivated croplands is working. Model
simulation results show that conservation practices reduced
the amount of sediment lost at the edge-of-field from 54.1
million tons (no-practice scenario) to 24.9 million tons of
sediment (2003-06 baseline condition) to 9.9 million tons of
sediment (2011 conservation condition) (table 5.3; fig. 5.6).
Relative to 2003-06 baseline condition, conservation practices
in place in 2011 reduced edge-of-field sediment losses by 60
percent. Similar reductions were achieved on sediment loads
delivered to rivers and streams each year. Sediment losses to
rivers and streams of roughly 21.1 million tons under the nopractice scenario were reduced 9.6 and 3.9 million tons of
sediment under 2003-06 baseline condition and 2011
conservation condition, respectively (table 5.4). The 2011
conservation condition reduced the delivery of sediment to the
Bay by about 22 and 8 percent relative to the no-practice
scenario and the 2003-06 baseline condition, respectively
(table 5.5).
Although relative to the no-practice scenario, edge-of-field
sediment losses were reduced by 82 percent due to
conservation practices in place in 2011 (table 5.3),
opportunities to reduce sediment losses remain. For example,
the sediment loss reduction gains in the Susquehanna River
subregion are not as high a percentage as the conservation
gains in other subregions in the Chesapeake Bay. In the
Susquehanna River subregion, the 2011 conservation
condition reduced annual edge-of-field sediment losses by 78
percent (29.6 million tons) relative to the no-practice scenario
and by 59 percent (11.9 million tons) relative to the 2003-06
baseline condition. The 11.9 million ton reduction in edge-offield sediment loss accounted for nearly 79 percent of all the
15.1 million tons of sediment loss reduction in the 2011
conservation condition as compared to the 2003-06 baseline
condition. Model simulations show that without any
conservation in place, the Susquehanna River subregion would
account for 70 percent of the region’s edge-of-field sediment
losses. However, the Susquehanna River subregion, which
contains 46 percent of the Chesapeake Bay region’s cropland
accounted for 81 and 83 percent of edge-of-field sediment
losses under the 2003-06 baseline condition and the 2011
conservation condition, respectively. This subregion has a
higher proportion of cropland acres with greater vulnerability
to runoff, which likely require a greater level of conservation
practices to control and trap sediment (table 5.3).
With 2011 conservation practices in place, cultivated cropland
is the source of 46 percent of sediment loads delivered to
rivers and streams in the Chesapeake Bay watershed (table
5.6, fig. 5.6). As just noted, 83 percent of these losses occur in
one subwatershed, the Susquehanna River. Under 2011

conditions, runoff from forests, wetlands, range brush,
horticulture, and barren land contributed 25 percent of
sediment delivered to watershed outlets, while urban nonpoint
sources represented about 21 percent of the total sediment load
delivered to streams and rivers. Under 2011 conditions
hayland, pasture and grazing land, and point sources each
contributed 5 percent or less of the total sediment delivered to
watershed outlets (table 5.6).
Under the 2011 conservation condition, instream loads—the
amount of sediment delivered from all sources to the
Chesapeake Bay after accounting for instream deposition and
transport processes—averaged about 7.0 million tons, down
from 7.6 million and 9.0 million tons of sediment delivered to
the Bay under the 2003-06 baseline condition and the nopractice scenario, respectively (table 5.5, fig. 5.6).
Under the 2011 conservation condition, the Upper Chesapeake
Bay contributed 64 percent of the instream sediment loads,
while the Lower Chesapeake Bay contributed 36 percent
(table 5.5). Instream loads were greatest from the
Rappahannock, York, and James Rivers subregion of the
Lower Chesapeake Bay and the Potomac River subregion of
the Upper Chesapeake Bay (table 5.5), which accounted for 35
and 34 percent of sediment delivered to the Chesapeake Bay,
respectively. The large contributions of these subregions are
due in part to their proximity to the Bay, which reduces
opportunities for sediment deposition during transport.
Transport processes are an important consideration in
sediment conservation. Under the 2011 conservation
condition, the Susquehanna River subregion delivered more
sediment to rivers and streams (53 percent of sediment from
all sources) than did the Potomac River (17 percent of
sediment from all sources; table 5.6). However, the
Susquehanna River’s instream load contribution to the
Chesapeake Bay only accounts for 18 percent of the total
instream sediment load from all sources, while the Potomac
River instream contribution accounts for 34 percent of the
total instream load from all sources (table 5.5). The
Conowingo Reservoir, located just above the outlet of the
Susquehanna River, traps a significant portion of the sediment
from the Susquehanna River, preventing its transport to the
Bay.
The Upper Chesapeake subregion had the highest percent
reduction in instream loads delivered to the Bay due to
conservation practice adoption. Relative to the no-practice
scenario, instream loads were reduced by 35 percent in the
2003-06 baseline condition and 50 percent in the 2011
conservation condition, (table 5.5). Of all the subregions, the
Upper Chesapeake subregion also had the greatest percentage
decrease in sediment delivered to the Chesapeake Bay, which
dropped by 26 percent between the 2003-06 baseline condition
and the 2011 conservation condition.

81

Subregion
code
0205
0206
0207
0208

Subregion name
Susquehanna River
Upper Chesapeake**
Potomac River
Lower Chesapeake**
Total

Load reductions due to conservation practices
(percent change)
2003-06
2011
2011
Vs.
Vs.
vs.
No-practice
No-practice
2003-06
47
78
59
67
92
77
74
87
51
69
91
72
54
82
60

Subregion
code
0205
0206
0207
0208

Subregion name
Susquehanna River
Upper Chesapeake**
Potomac River
Lower Chesapeake**
Total

Load reductions due to conservation practices
(percent change)
2003-06
2011
2011
vs.
vs.
vs.
No-practice
No-practice
2003-06
47
78
59
67
91
74
74
87
51
68
91
72
54
82
60

Note: Percent reductions were calculated prior to rounding the values for reporting in the table and the associated text. The differences between loadings in this table and table 5.3 are due to the application of delivery ratios,
which were used to simulate delivery of sediment from the edge-of-field to the watershed outlet (8-digit HUC). Some columns do not add to totals because of rounding.
* See Figure 5.4.
** Excludes watersheds that drain into the Atlantic Ocean (8-digit HUCs 02060010 and 02080110).

8-digit
HUC
group*
I
II
III
IV + V

Conservation Practice Impacts
(1,000 tons)
2011
2003-06
Conservation
Baseline
No-practice
condition
condition
scenario
3,161
7,662
14,495
152
577
1,768
369
753
2,922
173
616
1,919
3,854
9,608
21,104

Table 5.4. Average annual sediment loads delivered to watershed outlets (8-digit HUCs) from cultivated cropland for the four subregions in the Chesapeake Bay watershed: nopractice scenario, 2003-06 baseline condition, and 2011 conservation condition.

Note: Percent reductions were calculated prior to rounding the values for reporting in the table and the associated text. Loads represent both cropped acres and land in long-term conserving cover. Some columns do not add to
totals because of rounding.
* See Figure 5.4.
** Excludes watersheds that drain into the Atlantic Ocean (8-digit HUCs 02060010 and 02080110).

8-digit
HUC
group*
I
II
III
IV + V

Conservation Practice Impacts
(1,000 tons)
2011
2003-06
Conservation
Baseline
No-practice
condition
condition
scenario
8,198
20,141
37,827
338
1,461
4,496
924
1,905
7,272
399
1,415
4,508
9,859
24,922
54,100

Table 5.3. Average annual sediment loads delivered to edge-of-field (APEX model output) from cultivated cropland for the four subregions in the Chesapeake Bay watershed: the
no-practice scenario, 2003-06 baseline condition, and 2011 conservation condition.

82

0205
0206
0207

0208
0208

I
II
III

IV
V

Lower Chesapeake Bay
Rappahannock, York, and James Rivers
Eastern and Western Shores

Subregion name
Upper Chesapeake Bay
Susquehanna River
Upper Chesapeake
Potomac River

Sub-total
Total

Sub-total

2,458
74
2,532
6,992

1,270
809
2,381
4,460

2,634
83
2,717
7,566

1,279
1,053
2,518
4,849

2,989
108
3,097
9,008

1,284
1,609
3,018
5,911

No-practice
scenario

12
23
12
16

<1
35
17
18

0205
0206
0207
0208

0205
0206
0207
0208

I
II
III
IV + V

I
II
III
IV + V

Susquehanna River
Upper Chesapeake****
Potomac River
Lower Chesapeake****
Total

Susquehanna River
Upper Chesapeake****
Potomac River
Lower Chesapeake****
Total

Subregion name

52
13
17
18
100

4,393
1,058
1,389
1,514
8,354

All sources

38
2
4
2
46

3,161
152
369
173
3,854

Cultivated
cropland*

* Includes land in long-term conserving cover, excludes horticulture.
** Includes construction sources and urban land runoff.
*** Includes forests (all types), wetlands, range brush, horticulture, and barren land.
**** Excludes watersheds that drain into the Atlantic Ocean (8-digit HUCs 02060010 and 02080110).

Subregion code

8-digit
HUC
group

3
<1
1
1
5

259
5
65
60
389

Hayland

Pasture and
grazing land
Amount (1,000 tons)
78
52
70
144
344
Percent of all sources
1
1
1
2
4

6
4
6
5
21

482
322
497
432
1,734

Non-point
sources**

Urban

<1
<1
<1
<1
<1

3
<1
1
3
7

Point sources

7
11
7
8

1
23
5
8

5
7
4
9
25

393
585
361
727
2,065

Forest and
other***

Table 5.6. Average annual sediment loads delivered to watershed outlets (8-digit HUCs) from all sources for the four subregions in the Chesapeake Bay watershed, 2011
conservation condition.

18
31
18
22

1
50
21
25

Load reductions due to conservation practices
(percent change)
2003-06
2011
2011
vs.
vs.
vs.
No-practice
No-practice
2003-06

* See Figure 5.4.
Note: Percent reductions were calculated prior to rounding the values for reporting in the table and the associated text. Some columns do not add to totals because of rounding.

Subregion
code

8-digit
HUC
group*

Conservation Practice Impacts
(1,000 tons)
2011
2003-06
Conservation
Baseline
condition
condition

Table 5.5. Average annual instream sediment loads (all sources) delivered to the Chesapeake Bay, 2011 conservation condition.

83

Figure 5.6. Estimates of average annual instream sediment loads for the 2003-06 baseline condition and 2011 conservation condition
with comparison to the no-practice and background scenarios for subregions in the Chesapeake Bay watershed.*

* Instream sediment loads delivered to the Chesapeake Bay (all sources) are shown for each of the four subregions, corresponding to estimates
presented in table 5.5. The total sediment load delivered to the Chesapeake Bay from all areas is shown in the bar chart in the lower right hand
corner, labeled “Sediment Load to Bay.”
Note: “Background sources” represent loads that would be expected if no acres in the watershed were cultivated. These estimates were derived by
running an additional scenario that simulated a grass and tree mix cover without any tillage or addition of nutrients for all cultivated cropland acres in
the watershed. “Background” loads include loads from all other land uses—hayland, pastureland, forestland, and urban land—as well as point
sources.

84

Total Nitrogen
The model simulations suggest that continued adoption of new
and improved conservation practices aimed at nitrogen load
reduction are working. Model simulation results show that
conservation practices reduced the amount of nitrogen lost at
the edge-of-field from 275.9 million pounds (no-practice
scenario) to 186.6 million pounds of nitrogen (2003-06
baseline condition) to 138.0 million pounds of nitrogen (2011
conservation condition) (table 5.7). Relative to the 2003-06
baseline condition, conservation practices in place in 2011
reduced edge-of-field nitrogen losses by 26 percent. The edgeof-field losses delivered to rivers and streams impact surface
water quality and do not include percolation losses to deep
aquifers. The nitrogen lost to deep percolation may become
trapped or may take many years to reach surface waters.
Similar reductions were achieved on nitrogen loads delivered
to rivers and streams each year: roughly 130.9 million pounds
of nitrogen were lost to rivers and streams each year in the
2003-06 baseline condition, a 30 percent reduction from the
no-practice scenario losses of 186.7 million pounds.
Conservation practices in use in 2011 reduced these losses to
104.2 million pounds, a 20 percent reduction from loss rates in
the 2003-06 baseline condition (table 5.8).
The 2011 conservation practices reduced the delivery of
nitrogen to the Bay by about 17 and 6 percent relative to the
no-practice scenario and the 2003-06 baseline condition,
respectively (table 5.9).
With 2011 conservation practices in place, cultivated cropland
is the source of 29 percent of nitrogen loads delivered to rivers
and streams in the Chesapeake Bay watershed (table 5.10, fig.
5.7). Roughly 41 percent of these losses occur in one
subwatershed, the Susquehanna River. Urban point sources

were the source of 27 percent of nitrogen loads delivered to
watershed outlets and urban non-point sources account for
another 10 percent; pasture and grazing land contributed 14
percent of the nitrogen load delivered to watershed outlets;
hayland contributed 8 percent of the total nitrogen delivered to
watershed outlets; and runoff from forests, wetlands, range
brush, horticulture, and barren land contributed 12 percent of
nitrogen delivered to watershed outlets (table 5.10).
Under 2011 conservation conditions, instream loads—the
amount of nitrogen delivered from all sources to the
Chesapeake Bay after accounting for instream deposition and
transport processes—averaged about 290.3 million pounds,
down from 309.8 million and 351.5 million pounds of nitrogen
delivered to the Bay under the 2003-06 baseline condition and
the no-practice scenario, respectively (table 5.9, fig. 5.7).
Transport processes are an important consideration in nitrogen
conservation. Nitrogen dynamics differ markedly from
sediment dynamics. For example, under the 2011 conservation
condition, the Susquehanna River subregion delivered 45
percent of nitrogen from all sources to rivers and streams,
while the Potomac River delivered 17 percent of nitrogen from
all sources; table 5.10). However, the Susquehanna River’s
instream load contribution to the Chesapeake Bay accounts for
41 percent of the total instream nitrogen load from all sources,
while the Potomac River instream contribution accounts for 21
percent of the total instream load from all sources (table 5.9).
Because of the solubility of nitrogen, the Conowingo
Reservoir, located just above the outlet of the Susquehanna
River, does not have the same impact on nitrogen dynamics as
it does on sediment dynamics. Nitrogen bound to sediment can
become soluble and move past the dam and into the
Chesapeake Bay.

85

Load reductions due to conservation practices
(percent change)
2003-06
2011
2011
vs.
vs.
vs.
No-practice
No-practice
2003-06
33
51
26
20
44
26
12
54
20
22
54
32
27
50
26

Subregion
code
0205
0206
0207
0208

Subregion name
Susquehanna River
Upper Chesapeake**
Potomac River
Lower Chesapeake**
Total

2011
Conservation
condition
62,179
21,783
12,833
7,401
104,200

Load reductions due to conservation practices
(percent change)
2003-06
2011
2011
vs.
vs.
vs.
No-practice
No-practice
2003-06
30
45
21
22
36
18
38
49
17
31
51
29
30
44
20

Note: Percent reductions were calculated prior to rounding the values for reporting in the table and the associated text. The differences between loadings in this table and table 5.7 are due to the application of delivery ratios,
which were used to simulate delivery of nitrogen from the edge-of-field to the watershed outlet (8-digit HUC). Some columns do not add to totals because of rounding.
* See Figure 5.4.
** Excludes watersheds that drain into the Atlantic Ocean (8-digit HUCs 02060010 and 02080110).

8-digit
HUC
group*
I
II
III
IV + V

Conservation Practice Impacts
(1,000 pounds)
2003-06
Baseline
No-practice
condition
scenario
78,330
112,440
26,681
34,181
15,411
25,042
10,424
15,021
130,850
186,680

Table 5.8. Average annual nitrogen source loads delivered to watershed outlets (8-digit HUCs) from cultivated cropland for the four subregions in the Chesapeake Bay watershed:
the no-practice scenario, 2003-06 baseline condition, and 2011 conservation condition.

Note: Percent reductions were calculated prior to rounding the values for reporting in the table and the associated text. Loads represent both cropped acres and land in long-term conserving cover. Some columns do not add to
totals because of rounding.
* See Figure 5.4.
** Excludes watersheds that drain into the Atlantic Ocean (8-digit HUCs 02060010 and 02080110).

watershed: the no-practice scenario, 2003-06 baseline condition, and 2011 conservation condition.
Conservation Practice Impacts
(1,000 pounds)
8-digit
Sub2011
2003-06
HUC
region
Conservation
Baseline
No-practice
group*
code
Subregion name
condition
condition
scenario
I
0205
Susquehanna River
81,074
110,080
163,970
II
0206
Upper Chesapeake**
29,009
39,224
51,538
III
0207
Potomac River
17,374
21,808
37,575
IV + V
0208
Lower Chesapeake**
10,540
15,455
22,765
Total
137,997
186,567
275,850

Table 5.7. Average annual nitrogen source loads delivered to edge-of-field (APEX model output) from cultivated cropland for the four subregions in the Chesapeake Bay

86

0205
0206
0207

0208
0208

I
II
III

IV
V

Lower Chesapeake Bay
Rappahannock, York, and James Rivers
Eastern and Western Shores

Subregion name
Upper Chesapeake Bay
Susquehanna River
Upper Chesapeake
Potomac River

Sub-total
Total

Sub-total

54,221
3,893
58,114
290,270

120,330
52,226
59,604
232,160

57,300
3,693
60,994
309,750

130,440
56,894
61,421
248,750

61,052
4,168
65,220
351,540

154,410
64,076
67,834
286,320

No-practice
scenario

6
11
6
12

16
11
9
13

11
7
11
17

22
18
12
19

Subregion code

0205
0206
0207
0208

0205
0206
0207
0208

8-digit
HUC
group

I
II
III
IV + V

I
II
III
IV + V

45
17
21
18
100

158,960
58,849
73,372
64,747
355,930

All sources

17
6
4
2
29

62,179
21,783
12,833
7,401
104,200

Cultivated
cropland*

* Includes land in long-term conserving cover, excludes horticulture.
** Includes construction sources and urban land runoff.
*** Includes forests (all types), wetlands, range brush, horticulture, and barren land.
**** Excludes watersheds that drain into the Atlantic Ocean (8-digit HUCs 02060010 and 02080110).

Susquehanna River
Upper Chesapeake****
Potomac River
Lower Chesapeake****
Total

Susquehanna River
Upper Chesapeake****
Potomac River
Lower Chesapeake****
Total

Subregion name

5
<1
2
1
8

19,276
591
5,455
2,892
28,214

Hayland

Pasture and
grazing land
Amount (1,000 tons)
27,639
4,380
11,241
7,615
50,876
Percent of all sources
8
1
3
2
14

2
1
3
3
10

8,305
4,639
10,867
10,408
34,219

Non-point
sources**

Urban

7
6
8
7
27

23,728
19,662
26,889
25,018
95,297

Point sources

5
2
2
3
12

16,880
7,796
6,092
11,411
42,179

Forest and
other***

Table 5.10. Average annual nitrogen loads delivered to watershed outlets (8-digit HUCs) from all sources for the four subregions in the Chesapeake Bay watershed, 2011
conservation condition.

5
-5
5
6

8
8
8
7

Load reductions due to conservation practices
(percent change)
2003-06
2011
2011
vs.
vs.
vs.
No-practice
No-practice
2003-06

*See Figure 5.7.
Note: Percent reductions were calculated prior to rounding reported values. Some columns do not add to totals because of rounding. The negative reduction simulated in the 2003-06 baseline condition and the 2011
conservation condition on the Eastern and Western Shores in HUC 0208 is due to higher nitrate loadings in 2011 relative to 2003-06.

Subregion
code

8-digit
HUC
group*

Conservation Practice Impacts
(1,000 tons)
2011
2003-06
Conservation
Baseline
condition
condition

Table 5.9. Average annual instream total nitrogen loads (all sources) delivered to the Chesapeake Bay, 2011 conservation condition.

87

Figure 5.7. Estimates of average annual instream nitrogen loads for the 2003-06 baseline condition and 2011 conservation condition
with comparison to the no-practice and background scenarios for subregions in the Chesapeake Bay watershed.*

* Instream nitrogen loads delivered to the Chesapeake Bay (all sources) are shown for each of the four subregions, corresponding to estimates
presented in table 5.9. The total sediment load delivered to the Chesapeake Bay from all areas is shown in the bar chart in the lower right hand
corner, labeled “Nitrogen Load to Bay.”
Note: “Background sources” represent loads that would be expected if no acres in the watershed were cultivated. These estimates were derived by
running an additional scenario that simulated a grass and tree mix cover without any tillage or addition of nutrients for all cultivated cropland acres in
the watershed. “Background” loads include loads from all other land uses—hayland, pastureland, forestland, and urban land—as well as point
sources.

88

Total Phosphorus
Model simulations suggest the continued adoption of new and
improved conservation practices aimed at phosphorus load
reduction are working. Model simulation results show that
conservation practices reduced the amount of phosphorus lost
at the edge-of-field from 37.3 million pounds (no-practice
scenario) to 15.6 million pounds of phosphorus (2003-06
baseline condition) to 8.5 million pounds of phosphorus (2011
conservation condition) (table 5.11; fig. 5.8). Relative to the
2003-06 baseline condition conservation practices in place in
2011 reduced edge-of-field phosphorus losses by 46 percent.
Similar reductions were achieved on phosphorus loads
delivered to rivers and streams each year: roughly 5.7 million
pounds of phosphorus were lost to rivers and streams each
year under the 2003-06 baseline condition, a 59 percent
reduction from losses in the no-practice scenario (13.7 million
pounds). Conservation practices in use in 2011 reduced these
losses to 3.4 million tons, a 41 percent reduction from 2003-06
loss rates (table 5.12). The 2011 conservation condition
reduced the delivery of phosphorus to the Chesapeake Bay by
about 21 and 5 percent relative to the no- practice scenario and
the 2003-06 baseline condition, respectively (table 5.13).
Although relative to the no-practice scenario, edge-of-field
phosphorus losses were reduced by 77 percent due to
conservation practices in place in 2011 (table 5.11),
opportunities to reduce phosphorus losses remain. Phosphorus
conservation trends are similar to trends in sediment loss
reduction, although they are not identical due to the behavior
of the soluble form of phosphorus. For example, the
Susquehanna River subregion accounted for a greater
percentage of total edge-of-field sediment losses over all three
scenarios, highlighting the greater proportion of cropland and
greater inherent runoff as compared to the other subregions.
Similarly, phosphorus losses in the Susquehanna River
subregion, accounted for 62, 72, and 75 percent of edge-offield phosphorus losses under the no-practice scenario, 200306 baseline condition, and 2011 conservation condition,
respectively (table 5.11). Conservation practice adoption
impact on phosphorus reduction in the Susquehanna was
significant. Annual phosphorus losses were reduced by 73
percent (16.8 million pounds) under 2011 conservation
condition, relative to the no-practice scenario, and by 43
percent (4.9 million pounds) relative to the 2003-06 baseline
condition (table 5.11).
With 2011 conservation practices in place, cultivated cropland
is the source of 11 percent of phosphorus loads delivered to
rivers and streams in the Chesapeake Bay watershed (table
5.14, fig. 5.8). Approximately 72 percent of these losses occur
in one subwatershed, the Susquehanna River. Under the 2011
conditions, point sources were the source of 37 percent of
phosphorus loads delivered to watershed outlets. Pasture and
grazing land contributed 28 percent of the phosphorus load

delivered to watershed outlets. Runoff from point sources
contributed 10 percent of phosphorus loads delivered to
watershed outlets. Runoff from forests, wetlands, range brush,
horticulture, and barren land contributed 8 percent of
phosphorus delivered to watershed outlets. Hayland
contributed 5 percent of total phosphorus delivered to
watershed outlets (table 5.14).
Under the 2011 conservation condition, instream loads—the
amount of phosphorus delivered from all sources to the
Chesapeake Bay after accounting for instream deposition and
transport processes—averaged about 14.3 million pounds,
down from 15.1 million and 18.1 million pounds of
phosphorus delivered to the Bay under the 2003-06 baseline
condition and the no-practice scenario, respectively (table
5.13, fig. 5.8).
Under the 2011 conservation condition, the Upper Chesapeake
Bay contributed 65 percent of the instream phosphorus loads,
while the Lower Chesapeake Bay contributed 35 percent
(table 5.13). Instream loads were greatest from the
Rappahannock, York and James Rivers subregion of the
Lower Chesapeake Bay and the Susquehanna River subregion
of the Upper Chesapeake Bay (table 5.13), which accounted
for 33 and 25 percent of phosphorus delivered to the
Chesapeake Bay, respectively. The large contributions of these
subregions are due in part to their proximity to the Bay, which
reduces opportunities for sediment-bound phosphorus
deposition during transport.
Transport processes are an important consideration in
phosphorus conservation. Under 2011 conservation
conditions, the Susquehanna River subregion delivered more
phosphorus to rivers and streams (41 percent of phosphorus
from all sources) than did the Potomac River (19 percent of
phosphorus from all sources) (table 5.14). The Susquehanna
River’s instream load contribution to the Chesapeake Bay only
accounts for 25 percent of the total instream phosphorus load
from all sources, while the Potomac River instream
contribution accounts for 20 percent of the total instream load
from all sources (table 5.13). The Conowingo Reservoir,
located just above the outlet of the Susquehanna River, traps a
significant portion of sediment-bound phosphorus from the
Susquehanna River, preventing its transport to the Bay.
However, note that the reduction was not as significant as was
reported for the dam’s impact on sediment retention. This is
because phosphorus has both an insoluble form, typically
associated with sediment, and a soluble form, which is
dissolved in water and may bypass the dam.

89

Subregion
code
0205
0206
0207
0208

Subregion name
Susquehanna River
Upper Chesapeake**
Potomac River
Lower Chesapeake**
Total

2011
Conservation
condition
6,383
562
1,004
519
8,468

Load reductions due to conservation practices
(percent change)
2003-06
2011
2011
vs.
vs.
vs.
No-practice
No-practice
2003-06
51
73
43
71
88
60
70
83
43
68
85
54
58
77
46

Subregion
code
0205
0206
0207
0208

Subregion name
Susquehanna River
Upper Chesapeake**
Potomac River
Lower Chesapeake**
Total

2011
Conservation
condition
2,406
282
434
241
3,363

Load reductions due to conservation practices
(percent change)
2003-06
2011
2011
vs.
vs.
vs.
No-practice
No-practice
2003-06
52
70
38
72
86
49
67
80
40
67
83
48
59
75
41

Note: Percent reductions were calculated prior to rounding the values for reporting in the table and the associated text. The differences between loadings in this table and table 5.11 are due to the application of delivery ratios,
which were used to simulate delivery of phosphorus from the edge-of-field to the watershed outlet (8-digit HUC). Some columns do not add to totals because of rounding.
* See Figure 5.4.
** Excludes watersheds that drain into the Atlantic Ocean (8-digit HUCs 02060010 and 02080110).

8-digit
HUC
group*
I
II
III
IV + V

Conservation Practice Impacts
(1,000 pounds)
2003-06
Baseline
No-practice
condition
scenario
3,909
8,084
557
1,983
727
2,206
462
1,421
5,654
13,694

Table 5.12. Average annual phosphorus source loads delivered to watershed outlets (8-digit HUCs) from cultivated cropland for the four subregions in the Chesapeake Bay
watershed: the no-practice scenario, 2003-06 baseline condition, and 2011 conservation condition.

Note: Percent reductions were calculated prior to rounding the values for reporting in the table and the associated text. Loads represent both cropped acres and land in long-term conserving cover. Some columns do not add to
totals because of rounding.
* See Figure 5.4.
** Excludes watersheds that drain into the Atlantic Ocean (8-digit HUCs 02060010 and 02080110).

8-digit
HUC
group*
I
II
III
IV + V

Conservation Practice Impacts
(1,000 pounds)
2003-06
Baseline
No-practice
condition
scenario
11,294
23,218
1,404
4,766
1,765
5,793
1,130
3,477
15,594
37,254

Table 5.11. Average annual phosphorus source loads delivered to edge-of-field (APEX model output) from cultivated cropland for the four subregions in the Chesapeake Bay
watershed: the no-practice scenario, 2003-06 baseline condition, and 2011 conservation condition.

90

0205
0206
0207

0208
0208

I
II
III

IV
V

Lower Chesapeake Bay
Rappahannock, York, and James Rivers
Eastern and Western Shores

Subregion name
Upper Chesapeake Bay
Susquehanna River
Upper Chesapeake
Potomac River

Sub-total
Total

Sub-total

4,792
159
4,952
14,346

3,657
2,833
2,904
9,394

4,889
170
5,059
15,094

3,988
3,018
3,030
10,036

5,327
257
5,584
18,055

4,858
4,054
3,558
12,471

10
38
11
21

25
30
18
25

0205
0206
0207
0208

0205
0206
0207
0208

I
II
III
IV + V

I
II
III
IV + V

Susquehanna River
Upper Chesapeake****
Potomac River
Lower Chesapeake****
Total

Susquehanna River
Upper Chesapeake****
Potomac River
Lower Chesapeake****
Total

Subregion name

41
13
19
27
100

12,473
3,874
5,758
8,238
30,343

All sources

8
1
1
1
11

2,406
282
434
241
3,363

Cultivated
cropland*

* Includes land in long-term conserving cover, excludes horticulture.
** Includes construction sources and urban land runoff.
*** Includes forests (all types), wetlands, range brush, horticulture, and barren land.
**** Excludes watersheds that drain into the Atlantic Ocean (8-digit HUCs 02060010 and 02080110).

Subregion
code

8-digit
HUC
group

3
<1
1
1
5

1,060
39
256
269
1,625

Hayland

Pasture and
grazing land
Amount (1,000 tons)
3,055
1,037
1,919
2,414
8,424
Percent of all sources
10
3
6
8
28

3
2
2
3
10

829
565
739
940
3,073

Non-point
sources**

Urban

14
5
6
12
37

4,299
1,459
1,971
3,545
11,273

Point sources

3
2
1
3
8

790
493
440
827
2,550

Forest and
other***

Table 5.14. Average annual phosphorus loads delivered to watershed outlets (8-digit HUCs) from all sources for the four subregions in the Chesapeake Bay watershed, 2011
conservation condition.

8
34
9
16

18
26
15
20

2
6
2
5

8
6
4
6

Load reductions due to conservation practices
(percent change)
2003-06
2011
2011
vs.
vs.
vs.
No-practice
No-practice
2003-06

*See Figure 5.4.
Note: Percent reductions were calculated prior to rounding the values for reporting in the table and the associated text. Some columns do not add to totals because of rounding.

Subregion
code

8-digit
HUC
group*

Conservation Practice Impacts
(1,000 tons)
2011
2003-06
Conservation
Baseline No-practice
condition
condition
scenario

Table 5.13. Average annual instream total phosphorus loads (all sources) delivered to the Chesapeake Bay, 2011 conservation condition.

91

Figure 5.8. Estimates of average annual instream phosphorus loads for the 2003-06 baseline condition and 2011 conservation
condition with comparison to the no-practice and background scenarios for subregions in the Chesapeake Bay watershed.*

* Instream phosphorus loads delivered to the Chesapeake Bay (all sources) are shown for each of the four subregions, corresponding to estimates
presented in table 5.13. The total sediment load delivered to the Chesapeake Bay from all areas is shown in the bar chart in the lower right hand
corner, labeled “Phosphorus Load to Bay.”
Note: “Background sources” represent loads that would be expected if no acres in the watershed were cultivated. These estimates were derived by
running an additional scenario that simulated a grass and tree mix cover without any tillage or addition of nutrients for all cultivated cropland acres in
the watershed. “Background” loads include loads from all other land uses—hayland, pastureland, forestland, and urban land—as well as point
sources.

92

Summary of Conservation Practice Effects
on Water Quality in the Chesapeake Bay
Watershed
Reductions in field-level losses due to conservation practices,
including maintaining land in long-term conserving cover,
translate into improvements in water quality in streams and
rivers. Transport of sediment and nutrients from farm fields to
streams and rivers involves a variety of processes and timelags, and not all of the potential pollutants leaving fields
contribute to current instream loads.
Cultivated cropland represents only about 10 percent of the
land base in the Chesapeake Bay watershed. At the 2003-06
baseline condition, relative to loads from all sources,
cultivated cropland delivered a disproportionate amount of
sediment and significant nutrients to rivers and streams and
ultimately to the Chesapeake Bay. Model simulations suggest
the long-term contributions of the conservation practices put
in place in the 2003-06 baseline condition and the 2011
conservation condition provide significant improvements
towards lessening agricultural losses of sediment and
nutrients. Of the total loads delivered to rivers and streams at
the 8-digit HUC watershed outlets from all sources, cultivated
cropland is the source for 46 percent of the sediment, 29
percent of the nitrogen, and 11 percent of the phosphorus.
Figures 5.9, 5.10, and 5.11 summarize the extent to which the
2003-06 baseline condition and the 2011 conservation
condition have reduced sediment, nitrogen, and phosphorus
loads in the Chesapeake Bay watershed, on the basis of model
simulations. In each figure, the top map shows delivery from
cultivated cropland to rivers and streams and the bottom map
shows delivery from all sources to the Chesapeake Bay. The
effects of the 2011 conservation condition are contrasted with
the effects of the 2003-06 baseline condition and the nopractice scenario.
Background levels, representing loads that would be expected
if no acres in the watershed were cultivated or treated with
conservation practices, are also shown in the bar charts. These
estimates simulate a grass and tree mix cover without any
tillage or addition of nutrients or pesticides for all cultivated
cropland acres in the watershed. Background loads also
include 2003-06 baseline condition loads from all other land
uses—hayland, pastureland, forestland, and urban land—as
well as point sources. In the 2003-06 report alternative
scenarios were developed to project the potential reductions
that could realized by targeting acres with different treatment
needs; that analysis was not repeated in this report.

Sediment Loss
In figure 5.9, the top map shows that the 2003-06 baseline
condition reduced sediment loads delivered from cropland to
rivers and streams in the watershed by 54 percent relative to
the no-practice scenario. The 2011 conservation condition
reduced sediment losses by 60 percent relative to the 2003-06
baseline condition.
The bottom map shows that when sediment loads from all
sources are considered, the use of conservation practices on
cropland reduced sediment loads delivered to the Chesapeake
Bay by 16 percent under the 2003-06 baseline condition as
compared to the no-practice scenario. The 2011 conservation
condition reduced total sediment loads delivered to the
Chesapeake Bay by 8 percent relative to the 2003-06 baseline
condition.

Total Nitrogen Loss
In Figure 5.10, the top map shows that 2003-06 baseline
condition reduced total nitrogen loads delivered from cropland
to rivers and streams in the watershed by 30 percent relative to
the no-practice scenario. The 2011 conservation condition
reduced nitrogen losses by 20 percent relative to the 2003-06
baseline condition.
The bottom map shows that the use of conservation practices
on cropland reduced total nitrogen loads delivered to the
Chesapeake Bay by 12 percent under the 2003-06 baseline
condition as compared to the no-practice scenario. The 2011
conservation condition reduced nitrogen loads delivered to the
Chesapeake Bay by 6 percent relative to the 2003-06 baseline
condition.

Total Phosphorus Loss
In Figure 5.11, the top map shows that the 2003-06 baseline
condition reduced total phosphorus loads delivered from
cropland to rivers and streams in the watershed by 59 percent
relative to the no-practice scenario. The 2011conservation
condition reduced phosphorus losses by 41 percent relative to
the 2003-06 baseline condition.
The bottom map shows that the use of conservation practices
on cropland reduced total phosphorus loads delivered to the
Chesapeake Bay by 16 percent under the 2003-06 baseline
condition as compared to the no-practice scenario. The 2011
conservation condition reduced phosphorus loads delivered to
the Chesapeake Bay by 5 percent as compared to the 2003-06
baseline condition.

93

Figure 5.9. Summary of the effects of conservation practices on sediment loads in the Chesapeake Bay watershed: no-practice
scenario, 2003-06 baseline condition, and 2011 conservation condition.

94

Figure 5.10. Summary of the effects of conservation practices on total nitrogen loads in the Chesapeake Bay watershed: no-practice
scenario, 2003-06 baseline condition, and 2011 conservation condition.

95

Figure 5.11. Summary of the effects of conservation practices on total phosphorus loads in the Chesapeake Bay watershed: nopractice scenario, 2003-06 baseline condition, and 2011 conservation condition.

96

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31 January 2010.

98

Appendix A
Land Use Data Used in this Report
The Chesapeake Bay region covers about 68,500 square miles
and includes parts of New York, Pennsylvania, Maryland,
Delaware, Virginia, and West Virginia, as well as the entire
District of Columbia. Fifty-nine percent of the land cover in
the Chesapeake Bay region is forest; it is primarily deciduous
forest, with some areas dominated by conifers and mixed
stands. Pastureland and hayland make up about 18 percent of
the land cover in the region, while 10 percent is used for crop
production. About 6 percent of the area is water and wetlands.
Urban areas make up about 8 percent of the Chesapeake Bay
region by area (table A1). The major metropolitan areas are
Washington, DC; Baltimore, MD; Richmond, VA; Norfolk
VA, and; Harrisburg, PA.
The 2007 Census of Agriculture reported that the 83,775
farms in the Chesapeake Bay region account for about 4
percent of the total number of farms in the United States and
occupy about 1 percent of all farmland in the nation.
According to the 2007 Census of Agriculture, in 2007
agriculture in the Chesapeake Bay region generated about $9.5
billion—24 percent from crops and 76 percent from livestock.

The Chesapeake Bay, the largest estuary in the United States,
is about 200 miles long and 30 miles wide at its widest point.
The Chesapeake Bay and its tributaries cover about 4,500
square miles of open water with over 11,600 miles of
shoreline, while the entire watershed covers about 68,500
square miles shared across six states (Delaware, Maryland,
New York, Pennsylvania, Virginia, and West Virginia) and the
District of Columbia. Per the most recent Census of
Agriculture, completed in 2007, agricultural land makes up
roughly 30 percent of the area and agriculture generates
roughly $9.5 billion annually. Cultivated cropland, including
land in continuous cover, makes up 10 percent of the region’s
acreage, while 20 percent is pasture, grassy or brushy range,
and hayland. Forest land covers about 58 percent and urban
land makes up 8 percent of the region. The remaining 4
percent of the area is in non-forested wetlands or is open
water.
A number of factors specific to cultivated cropland in the
Chesapeake Bay region contribute to a relatively high
vulnerability to soil and nutrient losses. These factors include
the region’s relatively high annual precipitation, cultivation on
highly erodible land, and cultivation of soils with high
vulnerability to surface water runoff and/or leaching.

Table A1. Distribution of land cover in the Chesapeake Bay region (USDA NRCS 2011).
Land use
Acres*
Cultivated cropland and land enrolled in the CRP general signup
4,588,332
Forest deciduous
19,106,747
Hay/Pasture not in rotation with crops
7,738,805
Urban
3,651,000
Water
1,152,262
Wetland forested
793,516
Rangeland – grasses
142,690
Wetland non-forested
517,632
Forest evergreen
2,999,538
Forest mixed
2,421,677
Rangeland – brush
266,807
Horticulture and barren
473,994
Totals
43,853,000

Percent
10
44
18
8
3
2
<1
1
7
6
1
1
100

Source: 2001 National Land Cover Database for the Conterminous United States (Homer et al. 2007).
*Acreage estimates for cultivated cropland differ slightly from those provided elsewhere in this report because of differences in sources and methods.

99

Appendix B
Simulating the No-Practice Scenario
The no-practice scenario provides an estimate of sediment and
nutrient loss from farm fields that would occur in the absence
of conservation practices. The benefits of conservation
practices in use within the Chesapeake Bay region were
estimated by contrasting model output from the no-practice
scenario to model output from the baseline conservation
conditions for 2003-06 and 2011. The no-practice
representations derived for use in this study conformed to the
following guidelines:
 Consistency: representation of all practices on all
sample points in a consistent manner, based on the
intended purpose of each practice;
 Simplicity: Complex rules for assigning “no-practice”
activities lead to complex explanations that are difficult
to substantiate and sometimes difficult to explain and
accept;
 Historical context avoided: The no-practice scenario is
a technological, not a chronological, step backward for
conservation It is also important to retain the overall
crop mix in the region, as it in part reflects market
forces. Taking away the conservation ethic is the goal;
 Moderation: The no-practice scenario should provide a
reasonable reduction in conservation practices so that
believable benefits of additional conservation practices
can be determined through comparison with baseline
conservation simulations; and
 Maintenance of crop yield or efficacy. It is impossible
to avoid small changes in crop yields, but care was
taken to avoid no-practice representations that would
significantly change crop yields and regional
production capabilities.
Table B1 summarizes the adjustments to conservation
practices used in simulation of the no-practice scenario.
No-practice representation of structural practices
The no-practice field condition for structural practices
simulates the absence of structural practices and uses a runoff
curve number for erosion prediction determined from a “poor”
soil condition.
 Overland flow. When practices affecting overland flow
of water and therefore the P factor of the USLE-based
equations were removed, the P factor was increased to
1. Slope length was also changed for practices such as
terraces, to reflect the absence of these slopeinterrupting practices in the no-practice scenario;
 Concentrated flow. The no-practice protocol removes
the structure or waterway that previously channelized
the flow and replaces it with a “ditch” as a separate
subarea. Although the ditch represents a gully, the only
sediment contributions from the gully come from
downcutting. Headcutting and sloughing of the sides
are not simulated in APEX;

 Edge-of-field. The no-practice protocol removes edgeof-field practices, restoring the slope length to what it
would be in the absence of the practices; and
 Wind control. Any practices reducing the unsheltered
distance are removed and the unsheltered distance set
to 400 meters.
No-practice representation of conservation tillage
The no-practice simulations remove conservation tillage and
cover crops benefits. Crops grown with a Soil Tillage Intensity
Rating (STIR value) below 100 are considered to be no- or
low-till systems and had tillage operations added to them in
the no-practice scenario. Specifically, because the most
common type of tillage operation reported was disking and the
most commonly reported disk implement was a tandem disk,
in the no-practice scenario two consecutive tandem disk
operations prior to planting were added. Two consecutive
disking operations add 78 to the existing tillage intensity,
which allows for more than 90 percent of the crops to exceed a
STIR of 100 and yet maintain the unique suite and timing of
operations for each crop in the rotation.
The hydrologic condition for assignment of the runoff curve
number on these acres was changed from “good” to “poor” on
all points receiving additional tillage. Points conventionally
tilled for all crops in the baseline condition scenario are
modeled with a “poor” hydrologic condition curve number.
No-practice representation of cover crops
The no-practice protocol for this practice removes the planting
of the crop and all associated cultural practices such as tillage,
fertilization, and includes consideration of grazing operations.
No-practice representation of irrigation practices
The no-practice irrigation protocols remove the benefits of
increased efficiencies of modern irrigation systems by
increasing water losses from the water source to the field,
evaporation losses with sprinkler systems, percolation losses
below the root-zone during irrigation, and runoff at the lower
end of the field.
The quantity of water applied for all scenarios was simulated in
APEX using an “auto-irrigation” procedure that applied
irrigation water when the degree of plant stress exceeded a
threshold. “Auto-irrigation” amounts were determined within
pre-set single event minimums and maximums, and an annual
maximum irrigation amount. APEX also used a pre-determined
minimum number of days before another irrigation event
regardless of plant stress. In the no-practice representation, all
conservation practices, such as Irrigation Water Management
and Irrigation Land Leveling, were removed.
No-practice representation of nutrient management
practices
The no-practice nutrient management protocols remove the
benefits of proper nutrient management techniques by altering
three of the four basic aspects of nutrient application—rate,
timing, and method. The form of application was not
addressed because of the inability to determine if proper form
was being applied.

100

Table B1. Construction of the no-practice scenario for the Chesapeake Bay region.
Practice adjusted
Criteria used to determine if a practice was Adjustments made to create the no-practice scenario
in use
Structural practices
Overland flow practices present
USLE P-factor changed to 1 and slope length increased
for points with terraces, soil condition changed good to
poor.
Concentrated flow—managed structures or
Structures and waterways replaced with earthen ditch,
waterways present
soil condition changed from good to poor.
Edge-of-field mitigation practices present
Removed practice and width added back to field slope
length.
Wind erosion control practices present
Unsheltered distance increased to 400 meters.
Residue and tillage
management

STIR ≤100 for any crop within a crop year

Add two tandem diskings 1 week prior to planting.

Cover crop

Cover crop planted for off-season protection

Remove cover crop simulation (field operations,
fertilizer, grazing, etc.).

Irrigation

Pressure systems

Change to hand-move sprinkler system except where the
existing system is less efficient.

Nitrogen rate

Total of all applications of nitrogen
(commercial fertilizer and manure
applications) ≤1.4 times harvest removal for
non-legume crops, except for cotton and small
grain crops

Increase rate to 1.98 times harvest removal
(proportionate increase in all reported applications,
including manure).

Total of all applications of nitrogen
(commercial fertilizer and manure
applications) ≤1.6 times harvest removal for
small grain crops

Increase rate to 2.0 times harvest removal (proportionate
increase in all reported applications, including manure).

Total of all applications of nitrogen
(commercial fertilizer and manure
applications) for cotton ≤60 pounds per bale

Increase rate to 90 pounds per bale (proportionate
increase in all reported applications, including manure).

Phosphorus rate

Applied total of fertilizer and manure
phosphorus over all crops in the crop rotation
≤ 1.1 times total harvest—phosphorus
removal over all crops in rotation.

Increase commercial phosphorus fertilizer application
rates to reach 2.2 times harvest removal for the crop
rotation (proportionate increase in all reported
applications over the rotation), accounting also for
manure phosphorus associated with increase to meet
nitrogen applications for no-practice scenario. Manure
applications were NOT increased to meet the higher
phosphorus rate for the no-practice scenario.

Commercial fertilizer
application method

Incorporated or banded

Change to surface broadcast.

Manure application
method

Incorporated, banded, or injected

Change to surface broadcast.

Commercial fertilizer
application timing

Within 3 weeks prior to planting, at planting,
or within 60 days after planting.

Moved to 3 weeks prior to planting. Manure
applications were not adjusted for timing in the nopractice scenario.

101

Nitrogen rate. For the no-practice scenario, the amount of
commercial nitrogen fertilizer applied was—
 increased to 1.98 times harvest removal for nonlegume crops receiving less than or equal to 1.40 times
the amount of nitrogen removed at harvest in the
baseline scenario, except for cotton and small grain
crops;
 increased to 2.0 times harvest removal for small grain
crops receiving less than or equal to 1.60 times the
amount of nitrogen removed at harvest in the baseline
scenario; and
 increased to 90 pounds per bale for cotton crops
receiving less than 60 pounds of nitrogen per bale in
the baseline scenario.

Timing of application. Nutrients applied closest to the time
when a plant needs them are the most efficiently utilized and
least likely to be lost to the surrounding environment. All
commercial fertilizer applications occurring within 3 weeks
prior to planting, at planting, or within 60 days after planting
were moved back to 3 weeks prior to planting for the nopractice scenario. For example, split applications that occur
within 60 days after planting are moved to a single application
3 weeks before planting. Timing of manure applications was
not adjusted in the no-practice scenario.

Where nitrogen was applied in multiple applications, each
application was increased proportionately. For sites receiving
manure, the threshold for identifying good management was
the total nitrogen application rate from both manure and
fertilizer, and both fertilizer and manure were increased
proportionately to reach the no-practice scenario rate.

No-practice representation of land in long-term conserving
cover
The no-practice representation of land in long-term conserving
cover is cultivated cropping with no conservation practices in
use. Cropped sample points were matched to each CRP
sample point on the basis of slope, soil texture, soil hydrologic
group, and geographic proximity. The cropped sample points
that matched most closely were used to represent the cropped
condition that would be expected at each CRP sample point if
the field had not been enrolled in CRP. In most cases, seven
“donor” points were used to represent the crops that were
grown and the various management activities to represent
crops and management for the CRP sample point “as if” the
acres had not been enrolled in CRP. The crops and
management activities of each donor crop sample were
combined with the site and soil characteristics of the CRP
point for the no-practice representation of land in long-term
conserving cover.

Phosphorus rate. For the no-practice scenario, the amount of
commercial phosphorus fertilizer applied was increased to 2.2
times the harvest removal rate. For crops receiving manure,
any increase in phosphorus from manure added to meet the
nitrogen criteria for no-practice was taken into account in
setting the no-practice application rate. However, no
adjustment was made to manure applied at rates below the P
threshold because the appropriate manure rate was based on
the nitrogen level in the manure. The ratio of 2.2 for the
increased phosphorus rate was determined by the average rateto-yield-removal ratio for crops with phosphorus applications
exceeding 1.1 times the amount of phosphorus taken up by all
the crops in rotation and removed at harvest. Multiple
commercial phosphorus fertilizer applications were increased
proportionately to meet the 2.2 threshold.

Method of application. Nutrient applications, including
banded or incorporated manure applications, were changed to
a surface broadcast application method.

102

Appendix C
Estimates of Margins of Error for
Selected Acre Estimates
The 2003-06 CEAP cultivated cropland sample is a subset of
NRI sample points from the 2003 NRI (USDA NRCS 2007).
The 2001, 2002, and 2003 Annual NRI surveys were used to
draw the sample. (Information about the CEAP sample design
is in “NRI-CEAP Cropland Survey Design and Statistical
Documentation,” available at
http://www.nrcs.usda.gov/technical/nri/ceap.) The 2011 CEAP
cultivated cropland sample is a subset of the 2007 NRI. The
2003-06 sample for cropped acres consists of 771 sample
points in the Chesapeake Bay region, while the 2011 sample
consists of 904 sample points. Acres reported using the CEAP
sample are “estimated” acres because of the uncertainty
associated with statistical sampling.
Statistics derived from the CEAP database are based upon data
collected at sample sites located across all parts of the region.
This means that estimates of acreage are statistical estimates
and contain some amount of statistical uncertainty. Since the
NRI employs recognized statistical methodology, it is possible
to quantify this statistical uncertainty.

Margins of error are provided in table C1 for selected acres
estimates found elsewhere in the report. The margin of error is
a commonly used measure of statistical uncertainty and can be
used to construct a 95-percent confidence interval for an
estimate. The lower bound of the confidence interval is
obtained by subtracting the margin of error from the estimate;
adding the margin of error to the estimate forms the upper
bound. Measures of uncertainty (e.g., margins of error,
standard errors, confidence intervals, coefficients of variation)
should be taken into consideration when using CEAP acreage
estimates. The margin of error is calculated by multiplying the
standard error by the factor 1.96; a coefficient of variation is
the relative standard for an estimate, usually in terms of
percentages, and is calculated by taking 100 times the standard
error and then dividing by the estimate.
The precision of CEAP acres estimates depends upon the
number of samples within the region of interest, the
distribution of the resource characteristics across the region,
the sampling procedure, and the estimation procedure.
Characteristics that are common and spread fairly uniformly
over an area can be estimated more precisely than
characteristics that are rare or unevenly distributed.

103

Table C1. Margins of error for acre estimates based on the CEAP sample.
2003-06
Estimated
acres
Cropped Acres
Susquehanna River (subregion 0205)
1,734.8
Upper Chesapeake Bay (subregion 0206)
1,187.9
Potomac River (subregion 0207)
684.0
Lower Chesapeake Bay (subregion 0208)
673.2
Chesapeake Bay region
4,279.9
Highly erodible land (HEL)
Susquehanna River (subregion 0205)
847.1
Upper Chesapeake Bay (subregion 0206)
133.3
Potomac River (subregion 0207)
334.5
Lower Chesapeake Bay (subregion 0208)
102.4
Chesapeake Bay region
1,417.2
Irrigated acres
Susquehanna River (subregion 0205)
19.7
Upper Chesapeake Bay (subregion 0206)
144.3
Potomac River (subregion 0207)
4.8
Lower Chesapeake Bay (subregion 0208)
40.2
Chesapeake Bay region
209.0
Acres receiving manure
Susquehanna River (subregion 0205)
913.6
Upper Chesapeake Bay (subregion 0206)
401.8
Potomac River (subregion 0207)
294.0
Lower Chesapeake Bay (subregion 0208)
7.8
Chesapeake Bay region
1,617.2
Cropping Systems (table 2.3)
Corn-soybean only
1,174.7
Corn-soybean with close grown crops
797.6
Corn only
690.4
Soybean only
161.1
Soybean-wheat only
124.7
Soybean and close grown crops
6.8
Corn and close grown crops
272.4
Vegetable or tobacco with or without other crops
142.9
Hay-crop mix
627.0
Remaining mix of crops
282.3
Use of structural practices (table 2.1)
Overland flow control practices
1,607.0
Concentrated flow control practices
871.9
Edge-of-field buffering and filtering practices
582.1
One or more water erosion control practices
2,215.1
Wind erosion control practices
378.1
497.0
Use of cover crops
Conservation treatment levels for nitrogen application
management (4Rs) (fig. 2.4)
High level of treatment
209.5
Moderately high level of treatment
2,335.1
Moderate level of treatment
1,170.1
Low level of treatment
565.3

2003-06
Margin
of error

2011
Estimate
d acres

2011
Margin
of error

186.4
100.0
102.8
96.9
285.3

1,996.3
1,021.3
733.3
602.5
4,353.4

254.6
126.4
92.0
98.7
302.3

146.8
49.4
72.9
67.2
184.1

1,170.7
131.3
356.5
86.0
1,744.5

185.7
47.5
88.1
35.6
182.3

29.3
52.3
10.0
35.8
67.2

24.0
226.1
23.5
33.9
307.5

29.2
67.3
24.5
34.6
90.5

247.9
85.1
96.8
8.8
307.8

1,216.4
400.3
358.3
93.6
2,068.6

207.2
82.9
83.6
48.7
283.2

175.2
139.5
140.3
76.2
73.6
8.9
91.0
87.5
141.9
87.4

880.4
1,251.6
364.3
128.0
119.9
45.3
335.9
208.8
701.4
317.8

153.9
157.9
95.3
51.2
44.0
32.7
93.7
102.1
168.0
79.0

248.5
169.7
138.0
311.2
114.7
121.6

1,966.5
1,334.4
1,339.0
2,884.7
1,024.1
2,225.2

189.5
174.4
159.0
261.4
175.7
168.4

106.4
228.4
209.7
158.7

236.8
2,141.0
1,561.4
414.2

93.1
263.9
181.6
89.4

Significan
t
Difference

*
*

*
*
*
*
*

104

Table C1. Margins of error for acre estimates based on the CEAP sample (Cont’d).
2003-06 2003-06
Estimate Margin
d acres of error
Conservation treatment levels for phosphorus application
management (4Rs) (fig. 2.5)
High level of treatment
1,003.8
188.4
Moderately high level of treatment
1,621.6
224.8
Moderate level of treatment
829.2
225.3
Low level of treatment
825.3
211.4
Conservation treatment levels for water erosion control
practices (fig. 4.1)
High level of treatment
74.2
44.0
Moderately high level of treatment
539.1
117.9
Moderate level of treatment
2,075.8
248.2
Low level of treatment
1,590.8
191.3
Conservation treatment levels for nitrogen runoff control
(fig. 4.2)
High level of treatment
356.9
121.9
Moderately high level of treatment
1,922.6
205.0
Moderate level of treatment
1,532.5
226.6
Low level of treatment
468.0
153.6
Conservation treatment levels for nitrogen leaching control
practices (fig. 4.3)
High level of treatment
487.0
130.4
Moderately high level of treatment
2,161.6
258.0
Moderate level of treatment
1,000.7
198.2
Low level of treatment
630.7
178.3
Conservation treatment levels for phosphorus runoff control
(fig. 4.4)
High level of treatment
851.8
173.3
Moderately high level of treatment
1,774.3
239.3
Moderate level of treatment
984.0
190.5
Low level of treatment
669.8
188.6

2011
Estimate
d acres

2011
Margin
of error

1,180.5
1,405.7
779.3
987.9

155.6
144.7
195.3
151.1

696.1
1,447.6
1,647.4
562.3

116.5
197.9
212.5
140.4

*
*

1,513.9
1,723.4
912.4
203.7

159.8
199.6
192.7
57.6

*

819.2
1,981.8
1,049.6
502.8

150.8
229.9
135.0
123.7

*

1,665.8
1,559.5
701.1
427.0

162.0
217.1
147.8
104.4

*

Significant
Difference

*

*
*

105

Appendix D
Nutrient Management, Nitrogen and
Phosphorus Scoring Method

the entire rotation. Scoring for phosphorus timing and method
are based on the lowest score for all applications. Maximum
score for both nutrients is 60. Rate and timing have a
maximum of 20 each and proper method plus split application
of nutrients can add an additional 20 points, 10 points each.

Table D1 shows the scoring system for nitrogen and
phosphorus application management treatment levels. Scores
for nitrogen are for each crop and crop year and averaged over
the rotation length. For phosphorus, the scores are based on
Table D1. Scoring System for Nitrogen and Phosphorus application management treatment levels.
Application Category
All crops except small
grains

Small grains

Rotation

Timing

Method

Application Criteria
Nitrogen Rate
Total N Applied / N removed by Harvest

Score*

< 1.2
< 1.4
< 1.6
< 1.8
> 1.8
No N Applied

20
15
10
5
0
15

Total N Applied / N removed by Harvest
< 1.4
< 1.6
< 1.8
< 2.0
< 2.0
No N Applied

20
15
10
5
0
15

Phosphorus Rate
Total P Applied / P removed by Harvest
< 1.0
< 1.2
< 1.4
< 1.6
> 1.6

20
15
10
5
0

Timing and Method Scores are the same for both Nitrogen and Phosphorus
Application relative to Planting (Days)
> 45
0
> 21 but < 25
5
> 7 but < 21
10
+ or – 7
15
> 7 past planting
20
Split Applications
First application >21 days
First application >7 but <21 days
First application w/in 7 days of plant

0
5
10

Surface broadcast and no incorporation
Injection, knifed, banded or incorporation

0
10

*Scores for Nitrogen are for each crop and crop year and averaged over the rotation length. For phosphorus, the
scores are based on the entire rotation. Scoring for phosphorus timing and method are based on the lowest score
for all applications. Maximum score for both nutrients is 60.

106

column headings refer to the subregion code. The names of the
subregions are shown below:

Appendix E
Model Simulation Results for the
Baseline Conservation Condition for
the Four Subregions in the
Chesapeake Bay Region

Subregion code

Model simulation results presented in Chapter 4 for the
baseline conservation condition are presented in tables E1 and
E2 for the four subregions in the Chesapeake Bay region. The

0205

Subregion name
Susquehanna
River

0206

Upper Chesapeake

0207

Potomac River

0208

Lower Chesapeake

Table E1. Average annual estimates of water flow, erosion, and soil organic carbon for the baseline conservation condition for
cropped acres, by subregion, in the Chesapeake Bay region.
Model simulated outcome

2003-06
Chesapeake
Bay Region

0205

0206

0207

0208

4,279.9

1,734.8

1,187.9

684.0

673.2

Cropped acres (million acres)
Percent of acres in region
Highly erodible acres
Percent of acres highly erodible
Irrigated acres
Percent of acres irrigated
Manured acres
Percent of acres receiving manure

2011
Chesapeake
Bay Region
4,353.4

0205
1,996.3

0206
1,021.3

0207

0208

733.3

602.5

100.0

40.5

27.8

16.0

15.7

100.0

46.6

23.9

17.1

14.1

1,417.2

847.1

133.3

334.5

102.4

1,744.5

1,170.7

131.3

356.5

86.0

33.1

48.8

11.2

48.9

15.2

40.1

58.6

12.9

48.6

14.3

209.0

19.7

144.2

4.8

40.2

300.9

24.0

219.5

23.5

33.9

4.9

1.1

12.1

0.7

6.0

6.9

1.2

21.5

3.2

5.6

1,569.8

876.3

396.3

289.5

7.8

2,068.6

1,216.4

400.3

358.3

93.6

36.7

50.5

33.4

42.3

1.2

47.5

60.9

39.2

48.9

15.5

4,070.9

1,715.1

1,043.7

679.2

633.0

4,052.5

1,972.3

801.8

709.8

568.6

42.4

41.7

43.8

40.6

43.5

42.3

41.7

43.8

40.8

43.5

42.7

38.6

43.8

39.4

41.0

40.9

39.3

43.8

39.4

43.2

7.6

7.1

7.8

5.5

7.4

8.1

8.2

6.4

11.1

7.2

24.2

23.5

24.4

24.8

25.1

24.9

23.9

25.8

25.6

25.9

8.8

9.0

8.3

8.0

9.9

8.5

9.0

7.4

7.8

9.9

9.6

9.1

11.8

7.8

8.7

9.3

8.8

12.1

7.9

8.1

0.0

0.0

0.0

0.0

0.1

0.0

0.0

0.0

0.0

0.0

3.7

6.6

1.1

2.8

1.5

1.5

2.5

0.4

1.1

0.5

5.1

9.4

1.1

3.6

2.3

1.9

3.2

0.3

1.4

0.6

57.2

45.1

62.8

59.9

75.5

73.0

67.1

69.9

71.4

100.0

-182.2

-256.1

-128.0

-137.5

-132.7

-102.7

-151.2

-55.2

-75.6

-55.4

Water sources
Non-irrigated acres
Precipitation (average annual inches)
Irrigated acres
Precipitation (average annual inches)
Irrigation applied (average annual inches)
Water loss pathways (average annual inches)
Evapotranspiration
Surface water runoff
Subsurface water flow
Erosion and sediment loss (average annual
tons/acre)
Wind erosion
Sheet and rill erosion
Sediment loss at edge-of-field due to water
erosion
Soil organic carbon (average annual
pounds/acre)
Loss of soil organic carbon with wind and
water erosion
Change in soil organic carbon, including loss
of carbon with wind and water erosion

107

Table E2. Average annual estimates of nitrogen loss and phosphorus loss for the baseline conservation condition for cropped acres, by
subregion, in the Chesapeake Bay region.
2003-06
Chesapeake
Bay Region

0205

0206

0207

0208

4,279.9

1,734.8

1,187.9

684.0

673.2

4,353.4

1,996.3

1,021.3

733.3

602.5

8.8

9.8

7.5

8.5

8.6

8.9

9.9

7.4

8.5

8.8

31.8

23.8

40.3

29.6

40.0

36.4

33.6

36.8

38.1

42.7

95.0

103.0

87.5

105.7

76.7

104.6

107.0

105.4

108.7

90.2

135.6

136.6

135.3

143.7

125.3

149.9

150.5

149.6

155.3

141.7

88.9

78.0

97.8

93.9

96.9

98.5

90.2

105.5

103.7

107.4

14.2

15.7

13.0

14.7

12.0

17.4

18.9

17.2

17.0

13.4

Nitrogen loss through denitrification

3.0

3.6

2.1

4.3

1.7

4.9

5.7

3.4

6.0

3.6

Nitrogen lost with windborne sediment
Nitrogen loss with surface runoff ,
including waterborne sediment

0.1

0.0

0.1

0.0

0.2

0.1

0.1

0.1

0.0

0.1

15.7

23.7

6.6

15.6

11.7

9.8

13.7

3.5

9.9

7.0

Nitrogen loss in subsurface flow pathways

25.9

31.5

25.4

23.8

14.6

22.9

26.7

22.6

20.7

13.1

Total nitrogen loss for all loss pathways

58.9

74.5

47.2

58.3

40.1

55.0

65.1

46.8

53.5

37.2

-17.3

-24.1

-12.0

-13.8

-12.3

-10.8

-15.2

-6.3

-9.0

-5.9

Phosphorus (average annual pounds/acre)
Phosphorus applied as commercial fertilizer
and manure

23.9

28.7

17.8

30.0

15.8

25.2

29.3

20.2

26.4

18.2

Phosphorus in crop yield removed at harvest

14.8

13.5

15.6

16.1

15.4

15.8

14.7

16.9

16.6

16.9

Phosphorus lost with windborne sediment
Phosphorus lost to surface runoff,
including waterborne sediment and
soluble phosphorus in surface water
runoff and lateral flow into drainage
ditches

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

3.3

5.5

1.1

3.2

1.8

1.8

2.8

0.5

1.6

0.8

Soluble phosphorus loss to groundwater

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

Total phosphorus loss for all pathways

3.4

5.6

1.1

3.3

1.8

1.9

2.9

0.6

1.7

0.9

0.5

1.2

-0.9

3.1

-1.6

2.6

4.6

0.8

2.4

-0.6

Model simulated outcome
Nitrogen (average annual pounds/acre)

2011
Chesapeake
Bay Region

0205

0206

0207

0208

Nitrogen sources
Atmospheric deposition
Bio-fixation by legumes
Nitrogen applied as commercial fertilizer
and manure
All nitrogen sources
Nitrogen in crop yield removed at harvest
Nitrogen loss pathways
Nitrogen loss by volatilization

Change in soil nitrogen

Phosphorus loss pathways

Change in soil phosphorus

108

Appendix F
Criteria for Water Erosion Control
Treatment Levels
The sediment scoring shown in table F1 assigns mitigation
points for sediment conserving conservation practices for each
method of mitigating sediment loss: Avoid, Control, and Trap
(ACT). These points provide a means to evaluate the
differences between treatment levels. They are combined with
nutrient application scoring in loss matrices for surface loss of
nitrogen and phosphorus. Each mitigation technique (Avoid,
Control, Trap) addressed by a conservation practice is scored
on a scale of 20 points for a maximum score for any individual
practice of 60 points. The point assignment is based on
professional opinions of NRCS conservationists and based on
a practices’ relative ability to control sediment loss for that
mitigation technique. Two practices may receive the same
score and one be generally recognized as more efficient in
certain situations, but both are highly effective in their
mitigation of losses. For example, no-till and terraces both
score 20 points for controlling sediment runoff losses.

Terraces are physical barriers that slow runoff and help control
concentrate flow. However, terraces do not reduce rainfall
impact; soil may be dislodged and may move between
terraces, especially if crop residue is not present on the soil
surface. The residue cover from no-till provides a physical
barrier to raindrop impact and reduces dislodging of soil
particles and subsequent erosion. When applied correctly,
terraces and no till practices complement each other to reduce
erosion to acceptable levels on most land suitable for crop
production.
For each point, the sum from all practices applied is calculated
for each mitigation technique and as an overall score. For
incorporation with the nutrient application scores for
determining treatment levels for nitrogen and phosphorus
runoff, each mitigation pathway is adjusted to a maximum of 20
points so its scoring scale is equivalent to that for the maximum
scores for rate, timing, and method plus split application scores
from nutrient application management. For example, the
maximum score for avoiding sediment when all practices are
summed is 40, so all avoid scores are halved. The maximum for
control mitigation is 100 and that for trapping is 80.

Table F1. Criteria for Water Erosion Control Treatment Levels
Sediment Loss (Runoff) Only

Conservation Cover (327)

Avoid

Control

Trap

20

0

0

Conservation Crop Rotation (328)

5

0

0

Contour Buffer Strips (332)

0

20

10

Contour Farming (330)

0

5

0

Cover Crop (340)

0

20

10

Cross Wind Ridges (588)

0

5

0

Cross Wind Trap Strips (589C)

0

10

5

Dike (356)

0

5

5

Diversion (362)

0

10

0

Field Border (386)

0

0

5

Filter Strip (393)

2

0

20

Grade Stabilization Structure (410)

0

10

0

Grassed Waterway (412)

0

10

5

Hedgerow Planting (442)

0

0

5

Herbaceous Wind Barriers (603)

0

10

5

Residue and Tillage Management, No-till/Strip-Till/Direct Seed (329)

20

20

0

Residue and Tillage Management, Mulch-Till (345)

14

14

0

Residue and Tillage Management, Ridge Till (346)

10

14

0

Riparian Forest Buffer (391)

4

0

20

Riparian Herbaceous Buffer (390)

4

0

20

Stripcropping (585)

0

10

0

Terrace (600)

0

20

2

Vegetative Barriers (601)

0

5

5

Vegetative Treatment Area (635)

0

0

10

Windbreak/Shelterbelt Establishment (380)

0

5

5

109

Appendix G
Criteria for Four Classes of Soil
Runoff Potential
Criteria for four classes of soil runoff potential were derived
using a combination of soil hydrologic group, slope, and Kfactor, as shown in table G1.

Table G1. Criteria for Four Classes of Soil Runoff Potential.
Acres with
Acres with
Soil runoff
hydrologic
hydrologic soil
potential
soil Group A*
Group B*

Acres with
hydrologic soil
Group C*

All acres

Slope<4

Slope<2

Acres with
hydrologic soil
Group D*
Slope<2
and
K-factor<0.28**

None

Slope >=4 and <=6
and
K-factor<0.32**

Slope >=2 and <=6
and
K-factor<0.28**

Slope<2
and
K-factor>=0.28**

None

Slope >=4 and <=6
and
K-factor>=0.32**

Slope >=2 and <=6
and
K-factor>=0.28**

Slope >=2 and <=4

None

Slope>6

Slope>6

Slope>4

Low

Moderate

Moderately high

High

Note: About 40 percent of cropped acres in the Chesapeake Bay region are highly erodible land (HEL).
* Hydrologic soil groups are classified as:

Group A—sand, loamy sand, or sandy loam soils that have low runoff potential and high infiltration rates even when thoroughly
wetted.

Group B—silt loam or loam soils that have moderate infiltration rates when thoroughly wetted.

Group C—sandy clay loam soils that have low infiltration rates when thoroughly wetted.

Group D—clay loam, silty clay loam, sandy clay, silty clay, or clay soils that have very low infiltration rates when thoroughly
wetted.
** K-factor is a relative index of susceptibility of bare, cultivated soil to particle detachment and transport by rainfall. It is determined by
the composition of the soil, saturated hydraulic conductivity, and soil structure.

110

Appendix H
Criteria for Four Classes of Soil
Leaching Potential
Criteria for four classes of soil leaching potential were derived
using a combination of soil hydrologic group, slope, and Kfactor, as shown in table H1.

Table H1. Criteria for Four Classes of Soil Leaching Potential.
Acres with
Acres with
Soil leaching
soil
soil hydrologic
potential*
hydrologic
Group B**
Group A**
Low

Moderate

Moderately high

High

Acres with
soil hydrologic
Group C**

Acres with
soil hydrologic
Group D**

None

None

None

All acres except
organic soils

None

Slope <=12
and
K-factor>=0.24***
or slope>12

All acres except
organic soils

None

Slope>12

Slope >=3 and <=12
and
K-factor<0.24***

None

None

Slope<=12 or
acres classified
as organic
soils

Slope<3 and
K-factor <0.24***
or acres classified as
organic soils

Acres classified
as organic soils

Acres classified
as organic soils

Note: About 40 percent of cropped acres in the Chesapeake Bay region are highly erodible land.
*Coarse fragments (stones and rocks) in the soil make it easier for water to infiltrate rather than run off. If the coarse fragment content
of the soil was greater than 30 percent by weight, the soil leaching potential was increased two levels (moderate and moderately high
to high, and low to moderately high). If the coarse fragment content was greater than 10 percent but less than 30 percent, the soil
leaching potential was increased one level.
**Hydrologic soil groups are classified as:

Group A—sand, loamy sand, or sandy loam soils that have low runoff potential and high infiltration rates even when thoroughly
wetted.

Group B—silt loam or loam soils that have moderate infiltration rates when thoroughly wetted.

Group C—sandy clay loam soils that have low infiltration rates when thoroughly wetted.

Group D—clay loam, silty clay loam, sandy clay, silty clay, or clay soils that have very low infiltration rates when thoroughly
wetted.
***K-factor is a relative index of susceptibility of bare, cultivated soil to particle detachment and transport by rainfall. It is determined by
the composition of the soil, saturated hydraulic conductivity, and soil structure.

111