Assessment of Effects of Conservation Practices on the Chesapeake Bay

Summary of Findings

March 2011

Assessment of the Effects of
Conservation Practices on Cultivated
Cropland in the Chesapeake Bay Region

The Chesapeake Bay is the largest estuary in the United States. The Bay is about 200 miles long, and the Bay and its
tributaries cover about 4,500 square miles of open water. The Chesapeake Bay watershed covers about 68,500 square
miles in parts of six states (Delaware, Maryland, New York, Pennsylvania, Virginia, and West Virginia) and the District of
Columbia (fig. 1).
Agricultural land makes up less than 30 percent of the area of the watershed (10 percent cultivated cropland, and 18
percent pasture and hayland). Forest land covers about 59 percent and urban land about 8 percent of the watershed.
The balance of the area is in wetlands or is open water. The focus of the CEAP Chesapeake Bay study is on the 10
percent of the watershed that is cultivated cropland.

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Summary of Findings:
Assessment of the Effects of Conservation Practices on Cultivated Cropland in the Chesapeake Bay Region

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Figure 1. Location of the Chesapeake Bay watershed

SOURCE: TEXAS AGRILIFE RESEARCH, TEXAS A&M UNIVERSITY
Methodology Used for the Cropland Assessments
A simulation model was used to estimate the effects of
conservation practices that were in use during the period 2003
to 2006, but does not capture practices implemented since then.
The NRCS National Resources Inventory, a statistical survey of
conditions and trends in soil, water, and related resources on
U.S. non-Federal land, provided the statistical framework.
Information on farming activities and conservation practices was
obtained from a farmer survey. Using those data, conservation
practice effects were evaluated in terms of—
•
reductions in losses of sediment, nutrients, and pesticides
from farm fields;
•
enhancement of soil quality through increases in soil
organic carbon in the field; and
•
reductions in instream loads of sediment, nutrients, and
pesticides in the region’s rivers and streams.
The physical process models used in this study are mathematical
representations of the real world designed to estimate complex
and varying environmental events and conditions. To estimate
the effects of conservation practices, model simulation results
were used to make relative comparisons between two model
runs—one that includes conservation practices and one that
excludes conservation practices. All other aspects of the input
data and the model parameters were held constant. Model
results are scientifically defensible to the level of 4-digit
hydrologic unit code (HUC) (subregion) watersheds.
The assessment includes conservation practices in use regardless of how or why they came to be in use. It is not restricted to only
those practices associated with Federal conservation programs; the assessment also includes the conservation efforts of States,
independent organizations, and individual landowners and farm operators.

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Summary of Findings:
Assessment of the Effects of Conservation Practices on Cultivated Cropland in the Chesapeake Bay Region

Study Findings
The voluntary, incentives-based conservation approach is working. Farmers have made good progress in reducing
sediment, nutrient, and pesticide losses from farm fields through conservation practice adoption throughout the
Chesapeake Bay region. Most cropland acres have structural or management practices—or both—in place to control
erosion. Nearly half the cropland acres are protected by one or more structural practices, such as buffers or terraces.
Reduced tillage is used in some form on 88 percent of the cropland.
Adoption of conservation practices has reduced edge-of-field sediment loss by 55 percent, losses of nitrogen with
surface runoff by 42 percent, losses of nitrogen in subsurface flows by 31 percent, and losses of phosphorus (sediment
attached and soluble) by 41 percent.
Opportunities exist to further reduce sediment and nutrient losses from cropland. The assessment of conservation
treatment needs presented in this study identifies opportunities to contribute to improved water quality in the Bay.
The study found that 19 percent of cropped acres (810,000 acres) have a high level of need for additional conservation
treatment. Acres with a high level of need consist of the most vulnerable acres with the least conservation treatment
and the highest losses of sediment and nutrients. Model simulations show that adoption of additional conservation
practices on these 810,000 acres would, compared to the 2003–06 baseline, further reduce edge-of-field sediment loss
by 37 percent, losses of nitrogen with surface runoff by 27 percent, losses of nitrogen in subsurface flows by 20
percent, and losses of phosphorus (sediment-attached and soluble) by 25 percent.
Targeting enhances effectiveness and efficiency. Targeting critical acres significantly improves the effectiveness of
conservation practice implementation. Use of additional conservation practices on acres that have a high need for
additional treatment—acres most prone to runoff or leaching and with low levels of conservation practice use—can
reduce sediment and nutrient per-acre losses by over twice as much as treatment of acres with a low or moderate
conservation treatment need.
Comprehensive conservation planning and implementation are essential. The most critical conservation concern
related to cropland in the region is the need to reduce nutrient losses from farm fields, especially nitrogen in
subsurface flows. Suites of practices that include soil erosion control and comprehensive nutrient management—
appropriate rate, form, timing, and method of application—are required to simultaneously address soil erosion,
nutrient losses in runoff, and loss of nitrogen through leaching.
Cultivated cropland represents only about 10 percent of the land base in the Chesapeake Bay watershed. However,
cultivated cropland delivers 22 percent of the sediment, 31 percent of the nitrogen, and 28 percent of the phosphorus
to rivers and streams in the watershed. Figure 2 shows the distribution of land uses within the Bay watershed, and
figures 3 through 5 show the source of sediment, nitrogen, and phosphorus delivered to rivers and streams in the
watershed.

Summary of Findings:
Assessment of the Effects of Conservation Practices on Cultivated Cropland in the Chesapeake Bay Region

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Figure 2. Distribution of land use/cover types in the Chesapeake Bay watershed
Cultivated
cropland

10.5%

62.5%

5.9%

Hayland

12.6%

Pasture and
grazing land

8.6%

Urban land
Forest and other

Figure 3. Percentage of average annual sediment loads delivered to rivers
and streams in the Chesapeake Bay watershed, by source
Cultivated cropland
21.5%
23.0%

10.1%
39.5%

5.9%

Hayland
Pasture and grazing
land
Urban point and
non-point
Forest and other

Figure 4. Percentage of average annual nitrogen loads delivered to rivers
and streams in the Chesapeake Bay watershed, by source
Cultivated cropland
13.3%
Hayland
30.8%
Pasture and grazing
land

37.7%
6.3%
11.8%

Urban point and
non-point
Forest and other

Figure 5. Percentage of average annual phosphorus loads delivered to rivers
and streams in the Chesapeake Bay watershed, by source
Cultivated cropland
6.8%
28.3%

Hayland
Pasture and grazing
land

50.1%
7.4%
7.4%

Urban point and
non-point
Forest and other

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Summary of Findings:
Assessment of the Effects of Conservation Practices on Cultivated Cropland in the Chesapeake Bay Region

Need for Additional Conservation Treatment
The need for additional conservation treatment in the Chesapeake Bay watershed was determined by imbalances
between the level of conservation practice use and the level of inherent vulnerability. Areas of sloping soils are more
vulnerable to surface runoff and consequently to loss of sediment and soluble nutrients with overland flow of water;
areas of level, permeable soils are generally not vulnerable to sediment loss or nutrient loss through overland flow but
are more prone to nitrogen losses through subsurface pathways.
Three levels of treatment need were estimated:
•

A high level of need for conservation treatment exists where the loss of sediment and/or nutrients is greatest and
where additional conservation treatment can provide the greatest reduction in agricultural pollutant loadings.
Some 810,000 acres—19 percent of the cultivated cropland in the region—have a high level of need for additional
conservation treatment.

•

A moderate level of need for conservation treatment exists where the loss of sediment and/or nutrients is not as
great and where additional conservation treatment has less potential for reducing agricultural pollutant loadings.
Approximately 2.6 million acres—61 percent of the cultivated cropland in the region—have a moderate level of
need for additional conservation treatment.

•

A low level of need for conservation treatment exists where the existing level of conservation treatment is
adequate compared to the level of inherent vulnerability. Additional conservation treatment on these acres would
provide little additional reduction in sediment and/or nutrient loss. Approximately 872,000 acres—20 percent of
the cultivated cropland in the region—have a low level of need for additional conservation treatment.

Figures 6 through 9 show the average annual per-acre rates of sediment loss, nitrogen loss through surface and
subsurface pathways, and phosphorus loss among the three levels of treatment need. The red bar across each chart
represents the average loss across the region, and the green bar shows model simulations of losses that could be
achieved with full, comprehensive treatment of acres with high and moderate treatment needs for sediment and
nutrient loss.

Summary of Findings:
Assessment of the Effects of Conservation Practices on Cultivated Cropland in the Chesapeake Bay Region

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Figure 6. Average annual per-acre sediment
loss for three levels of conservation treatment
need, Chesapeake Bay Region

Average nitrogen loss with surface runoff
(pounds/acre)

Average sediment loss (tons/acre)

3.0

Figure 7. Average annual per-acre nitrogen
loss with surface runoff for three levels of
conservation treatment need, Chesapeake Bay
Region

2.5
2.0
1.5
1.0
0.5

18
16
14
12
10
8
6
4
2
0

0.0
Low

Moderate

Low

High

60
50
40
30
20
10
0
Low

Moderate

High

Level of need for additional conservation
treatment for one or more resource concerns

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Figure 9. Average annual per acre
phosphorus loss to surface water for three
levels of conservation treatment,
Chesapeake Bay Region
Average total phosphorus loss (pounds/acre)

Average nitrogen loss in subsurface flows
(pounds/acre)

70

High

Level of need for additional conservation
treatment for one or more resource concerns

Level of need for additional conservation
treatment for one or more resource concerns

Figure 8. Average annual per-acre nitrogen
loss with subsurface flow pathways for three
levels of conservation treatment need,
Chesapeake Bay Region

Moderate

8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0
Low

Moderate

High

Level of need for additional conservation
treatment for one or more resource concerns

Summary of Findings:
Assessment of the Effects of Conservation Practices on Cultivated Cropland in the Chesapeake Bay Region

Current and Potential Reductions in Sediment and Nutrient Loadings
Table 1 shows current and potential reductions in sediment, nitrogen, and phosphorus delivery to rivers and streams in
the Chesapeake Bay watershed and to the Bay itself.
Table 1. Current and potential reductions in sediment, nitrogen, and phosphorus loadings to surface waters, Chesapeake Bay
watershed
Reduction in load to rivers and streams
Reduction in load to the Bay (all sources)
Pollutant
Current
Potential additional
Current
Potential additional
- - - - - - - - - - - - - - - - - - - - - - - - - - Percent - - - - - - - - - - - - - - - - - - - - - - - - - - Sediment
57
84
10
6
Nitrogen
36
52
14
15
Phosphorus
39
51
14
12

The use of conservation practices on cropland has reduced total sediment and nutrient loads delivered to rivers and
streams in the watershed compared to conditions that would be expected without conservation practices: Sediment
loads have been reduced by 57 percent, total nitrogen loads by 36 percent, and total phosphorus loads by 39 percent.
Additional conservation practices on all cultivated cropland acres having high and moderate treatment needs could
further reduce sediment delivery to rivers and streams by 84 percent from current levels, total nitrogen loads by 52
percent, and total phosphorus loads by 51 percent.
The use of conservation practices on cropland has reduced total loads delivered to Chesapeake Bay from all sources in
the watershed compared to conditions that would be expected without conservation practices: Sediment loads have
been reduced by 10 percent, total nitrogen loads by 14 percent, and total phosphorus loads by 14 percent. Additional
conservation practices on all cultivated cropland acres having high and moderate treatment needs could further reduce
sediment delivery to the Bay by 6 percent from current levels, total nitrogen delivery by 15 percent, and total
phosphorus delivery by 12 percent.

The Potential of Cover Crops for Reducing Nonpoint Source Pollution
The evaluation of conservation practices and associated estimates of conservation treatment needs are based on
practice use derived from a farmer survey conducted during the years 2003 to 2006. Since that time, however, the six
States in the Chesapeake Bay watershed have continued to work with farmers to enhance conservation practice
adoption in a joint effort to reduce nonpoint source pollution contributing to water quality issues in the Bay. In
Maryland, for example, the state offered expanded incentive payments for the planting of cover crops starting in the
2008–09 growing season.
When used properly, cover crops protect the soil from erosion during the winter months, take up nutrients remaining
in the soil, and release plant available nutrients slowly over the subsequent cropping period, thereby reducing nutrient
leaching and runoff during the non-growing season. Figures 10 and 11 compare the percentage of cropped acres with
high or moderate treatment need to projected treatment need if winter cover crops were planted on all cultivated
cropland in the region.

Summary of Findings:
Assessment of the Effects of Conservation Practices on Cultivated Cropland in the Chesapeake Bay Region

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Figure 11. Percentage of cropped acres that
would be expected to have high or moderate
treatment need if cover crops were in use on
all acres, by resource concern, Chesapeake
Bay Region

70%

70%

60%

60%

50%

Percent of cropped acres

Percent of cropped acres

Figure 10. Percentage of cropped acres that
have high or moderate treatment need, by
resource concern, Chesapeake Bay Region

40%
30%
20%

50%
40%
30%
20%

10%
10%
0%
Sediment
loss

Nitrogen Phosphorus Nitrogen
lost with
loss to
loss in
runoff
surface subsurface
water
flows

High treatment need
Moderate treatment need

0%
Nitrogen Phosphorus Nitrogen
lost to
loss in
lost with
surface subsurface
runoff
water
flows
High treatment need
Moderate treatment need

Sediment
loss

River Basin Cropland Modeling Study Reports
The U.S. Department of Agriculture initiated the Conservation Effects Assessment Project (CEAP) in 2003 to determine the effects
and effectiveness of soil and water conservation practices on agricultural lands. The CEAP report Assessment of the Effects of
Conservation Practices on Cultivated Cropland in the Chesapeake Bay Region is the second is a series of studies covering the major
river basins and water resource regions of the contiguous 48 United States. It was designed to quantify the effects of conservation
practices commonly used on cultivated cropland in the Chesapeake Bay Watershed, evaluate the need for additional conservation
treatment in the region, and estimate the potential gains that could be attained with additional conservation treatment. This series
is a cooperative effort among USDA’s Natural Resources Conservation Service and Agricultural Research Service, Texas AgriLife
Research of Texas A&M University, and the University of Massachusetts.
Upper Mississippi River Basin
Chesapeake Bay Region
Ohio-Tennessee River Basins
Great Lakes Water Resource Region
Delaware River Watershed
Northeast Water Resource Region
South Atlantic-Gulf Water Resource Region
Missouri River Basin
Arkansas-White-Red River Basins
Texas Gulf Water Resource Region
Lower Mississippi River Basin
Souris-Red-Rainy Water Resource Regions
Pacific Northwest and Western Water Resource
Regions
Expect release of these reports through 2011.

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Summary of Findings:
Assessment of the Effects of Conservation Practices on Cultivated Cropland in the Chesapeake Bay Region