Conservation Effects 

Assessment Project (CEAP) 

JUNE 2010 

DRAFT 

Assessment of the Effects 

of Conservation Practices on 

Cultivated Cropland in the 

Upper Mississippi River 

Basin 

 
Draft June 2010 Page 2 

 
Draft June 2010 Page 1 

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 Cooperative State Research, Education, and Extension 

Service (CSREES—now National Institute of Food and Agriculture [NIFA])) in response to a general call for better 

accountability of how society would benefit from the 2002 Farm Bill’s substantial increase in conservation program 

funding (Mausbach and Dedrick 2004). 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 provide research and 

assessment on how to best use conservation practices in managing agricultural landscapes to protect and enhance 

environmental quality. 

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 forest land; 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. 

Research and assessment efforts were designed to estimate the effects and benefits of conservation practices through 

a mix of research, data collection, model development, and model application. Duriancik et al. (2008) summarize the 

accomplishments of CEAP through 2007. A vision for how CEAP can contribute to better and more effective 

delivery of conservation programs in the years ahead is addressed in Maresch, Walbridge, and Kugler (2008). 

Additional information on the scope of the project can be found at http://www.nrcs.usda.gov/technical/nri/ceap/. 

 
Draft June 2010 Page 2 

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), Texas AgriLife Research, and the University of 

Massachusetts. 

Natural Resources Conservation Service, USDA 

Daryl Lund, Project Coordinator, Beltsville, MD, Soil Scientist 

Jay D. Atwood, Temple, TX, Agricultural Economist 

Joseph K. Bagdon, Amherst, MA, Agronomist and Pest Management Specialist 

Jim Benson, Beltsville, MD, Program Analyst 

Jeff Goebel, Beltsville, MD, Statistician 

Kevin Ingram, Beltsville, MD, Agricultural Economist 

Robert L. Kellogg, Beltsville, MD, Agricultural Economist 

Jerry Lemunyon, Fort Worth, TX, Agronomist and Nutrient Management Specialist 

Lee Norfleet, Temple, TX, Soil Scientist 

Agricultural Research Service, USDA, Grassland Soil and Water Research Laboratory, Temple, TX 

Jeff Arnold, Agricultural Engineer 

Mike White, Agricultural Engineer 

Blackland Center for Research and Extension, Texas AgriLife Research, Temple, TX 

Tom Gerik, Director 

Santhi Chinnasamy, Agricultural Engineer 

Mauro Di Luzio, Research Scientist 

Arnold King, Resource Conservationist

David C. Moffitt, Environmental Engineer 

Kannan Narayanan, Agricultural Engineer 

Theresa Pitts, Programmer 

Steve Potter, Hydrologic and Biological Engineer 

Evelyn Steglich, Research Assistant 

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 Douglas Lawrence, Deputy Chief for Soil Survey and Resource Assessment, and 

Tommie Parham, Director of the Resources Inventory and Assessment Division, NRCS, and Wayne Maresch, William Puckett,

and Maury Mausbach, former Deputy Chiefs for Soil Survey and Resource Assessment, NRCS. 

Acknowledgements 

The modeling team thanks former NRCS Chiefs Arlen Lancaster and Bruce Knight for their support, guidance, and hands-on 

involvement in the project. The team also thanks the current NRCS Chief, Dave White, for his support in the completion and 

publication of the report. The team acknowledges the contributions of Alex Barbarika, Rich Iovanna, and Skip Hyberg USDAFarm Service Agency, for providing data on Conservation Reserve Program (CRP) practices and making contributions to the report;

Craig Cox and the CEAP Blue Ribbon Panel for providing advice on the study design and recommendations on report scope and 

content; Harold Coble, North Carolina State University, for assisting with the analysis of the integrated pest management (IPM) 

survey data; Dania Fergusson, Eugene Young, and Kathy Broussard, USDA-National Agricultural Statistics Service, for leading 

the survey data collection effort; Dennis Timlin and Attila Nemes, USDA-Agricultural Research Service, for assistance with 

modeling; Phil Gasssman, Center for Agricultural and Rural Development (CARD), Iowa State University, for participating with the 

team in the model development; Chris Jones, Laboratory Supervisor, Des Moines Water Works, Des Moines, IA, for providing 

information on water quality issues in Des Moines; Greg Johnson, USDA-NRCS, Portland, OR, for providing assistance with 

weather data; 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; Harvey Terpstra, Center for Survey Statistics and Methodology, Iowa State 

University, for providing the National Soils Information System (NASIS) database link to the NRI; Dean Oman, USDA-NRCS, 

Beltsville, MD, for geographic information systems (GIS) analysis support; Doug Helms, USDA-NRCS, for assistance with the 

Foreword; Peter Chen, Susan Wallace, George Wallace, and Karl Musser, Paradigm Systems, Beltsville, MD, for graphics 

support, National Resources Inventory (NRI) database support, Web site support, and calculation of standard errors; and many others 

who provided advice, guidance, and suggestions throughout the project. 

The team also acknowledges the many helpful and constructive suggestions and comments by over 100 reviewers who participated in

the scientific peer review of an earlier version of the report. 
Draft June 2010 Page 3 

Foreword 

The United States Department of Agriculture has a rich tradition of working with farmers and ranchers to enhance agricultural 

productivity and environmental protection. Conservation pioneer Hugh Hammond Bennett worked tirelessly to establish a nationwide 

Soil Conservation Service along with a system of Soil and Water Conservation Districts. The purpose of these entities, now as then, is 

to work with farmers and ranchers and help them select and apply conservation practices to enable their operations to produce food, 

forage, and fiber while conserving the Nation’s soil and water resources. 

USDA conservation programs are voluntary. Many provide financial assistance to producers to help encourage adoption of 

conservation practices. Others provide technical assistance to design and install conservation practices suitable to the goals of the 

agricultural operation and the soil, climatic, and hydrologic setting. 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 to 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 to maintain the long-term productivity of crop and pasture land; and 

 retire land too fragile for continued agricultural production by planting and maintaining on them grasses, trees, or wetland 

vegetation. 

Once soil conservation became a national priority, assessing the effectiveness of conservation practices has been important. Over the 

past several decades, the relationship between crop production and the landscape in which it occurs has become better understood in 

terms of the impact on sustainable agricultural productivity and the impact of agricultural production on other ecosystem services that 

the landscape has potential to generate. Accordingly, the objectives of USDA conservation policy have expanded along with the 

development of conservation practices to achieve them. 

This report on the Upper Mississippi River Basin is the first in a series of regional reports that continues the tradition within USDA of 

assessing the status, condition, and trends of natural resources to determine how to improve conservation programs to best meet the 

Nation’s needs. These reports use a sampling and modeling approach to quantify the environmental benefits that farmers and 

conservation programs are currently providing to society, and explore prospects for attaining additional benefits with further 

conservation treatment. Subsequent reports on cultivated cropland will be prepared for regions shown in the following map. 

 
Draft June 2010 Page 4 

Assessment of the Effects 

of Conservation Practices on Cultivated Cropland 

in the Upper Mississippi River Basin 

Contents Page

Executive Summary 6 

Chapter 1: Land Use and Agriculture in the Upper Mississippi River Basin 13 

Land Use 

Agriculture 

Watersheds 

Chapter 2: Overview of Sampling and Modeling Approach 19 

Scope of Study 

Overview of Sampling and Modeling Approach 

Chapter 3: The Baseline Conservation Condition 29 

Overview and Summary of Findings 

Structural Conservation Practices 

Residue and Tillage Management Practices 

Cover Crops 

Irrigation Management Practices 

Nutrient Management Practices 

Pesticide Management Practices 

Conservation Cover Establishment 

Chapter 4: Onsite (Field-Level) Effects of Conservation Practices 42 

Water 

Erosion and Sediment Loss 

Soil Organic Carbon 

Nitrogen Loss 

Phosphorus Loss 

Pesticide Residues and Environmental Risk 

Chapter 5: Offsite Water Quality Effects of Conservation Practices 85 

Summary of Results for the Entire Basin 

Summary of Results for the 14 Subbasins 

Chapter 6: Assessment of Conservation Treatment Needs 95 

Conservation Treatment Levels 

Inherent Vulnerability Factors 

Evaluation of Conservation Treatment 

Under-Treated Acres 

Chapter 7: Assessment of Potential Gains from Further Conservation Treatment 112

Simulation of Additional Water Erosion Control Practices 

Simulation of Additional Nutrient Management Practices 

Potential for Field-Level Gains 

Potential for Offsite Water Quality Gains 

References 137

Appendix A: Estimates of Acres and Standard Errors 

Appendix B: Summary Tables of NRI-CEAP Cropland Survey Responses for the Upper Mississippi River Basin 

Appendix C: Model simulation results on the baseline conservation condition for the 14 subbasins 
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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/umrbdocumentation/. Included are the following reports that provide details on the 

modeling and databases used in this study: 

 The CEAP-HUMUS National Water Quality Modeling System and Databases 

 Calibration and Validation of CEAP-HUMUS for the Upper Mississippi River Basin 

 Delivery Ratios and Sediment Balance for the Upper Mississippi River Basin 

 APEX Model Validation for CEAP 

 Documentation of Pesticide Risk Indicators Used in the CEAP Cropland Modeling 

 NRI-CEAP Cropland Survey Design and Statistical Documentation 

 Transforming Survey Data to APEX Model Input Files 

 Modeling Structural Conservation Practices for the Cropland Component of the National Conservation Effects Assessment 

Project 

 APEX Model Upgrades, Data Inputs, and Parameter Settings for Use in CEAP Cropland Modeling 

 APEX Calibration and Validation Using Research Plots in Tifton, Georgia 

 The Agricultural Policy Environmental EXtender (APEX) Model: An Emerging Tool for Landscape and Watershed 

Environmental Analyses 

 The Soil and Water Assessment Tool: Historical Development, Applications, and Future Research Directions 

 Historical Development and Applications of the EPIC and APEX Models 
Draft June 2010 Page 6 

Assessment of the Effects of Conservation Practices on 

Cultivated Cropland in the Upper Mississippi River Basin 

Executive Summary 

 

Good progress has been made on reducing sediment, nutrient, and pesticide losses from farm fields through 

conservation practice implementation in the Upper Mississippi River Basin, but a significant amount of 

conservation treatment remains to be done to reduce nonpoint agricultural sources of pollution to acceptable 

levels. 

 Use of soil erosion control practices is widespread, with most acres receiving some form of erosion 

control treatment. Nevertheless, about 15 percent of the cultivated cropland acres still have excessive 

sediment loss from fields and require additional erosion control practices. 

 Complete and consistent use of nutrient management (proper rate, form, timing, and method of 

application) is generally lacking throughout the region. About 62 percent of the cultivated cropland 

acres require additional nutrient management to reduce the loss of nitrogen or phosphorus from fields. 

 The most critical conservation concern in the region is loss of nitrogen through leaching. About 51 

percent of cropped acres require additional nutrient management to address excessive levels of 

nitrogen loss in subsurface flow pathways, including tile drainage systems. About 36 percent of 

cropped acres need treatment only for nitrogen loss in subsurface flow. 

 About 15 percent of the acres are critically under-treated, usually requiring treatment for multiple 

natural resource problems. These acres are among the most vulnerable acres in the region. 

 Nutrient loss from fields is within acceptable limits when soil erosion control practices are paired with 

management of rate, form, timing, and method of nutrient application that maximizes the availability 

of nutrients for crop growth while minimizing environmental losses. A suite of practices that includes 

both soil erosion control and consistent nutrient management is required to simultaneously address 

soil erosion and nitrogen leaching loss. 

 Treatment of erosion alone can exacerbate the nitrogen leaching problem because reducing surface 

water increases infiltration and, therefore, movement of soluble nitrogen into subsurface flow 

pathways. Soil erosion control practices are effective in reducing the loss of nitrogen in surface 

runoff, but for some acres the re-routing of surface water runoff to subsurface flow along with 

incomplete nutrient management results in a small net increase in total nitrogen loss from the field. 

 Conservation practices in the region have also been effective in reducing pesticide residues lost from 

fields as well as the associated environmental risk. 

 Conservation practices have the greatest effect on the more vulnerable acres, such as highly erodible 

land and soils prone to leaching. Targeted treatment of these vulnerable acres is the most efficient 

strategy for reducing sediment, nutrients, and pesticide loads to water bodies in the region. 
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This study was designed to quantify the effects of conservation practices commonly used on cultivated cropland in 

the Upper Mississippi River Basin (UMRB), evaluate the need for additional conservation treatment in the region, 

and estimate the potential gains that could be attained with additional conservation treatment. 

For purposes of this report, cultivated cropland includes land in row crops or close-grown crops (such as small 

grains), hay and pasture in rotation with row crops and close-grown crops, and cropland in long-term conserving 

cover. The UMRB has about 61 million acres of cultivated cropland—58 million cropped acres and about 3 million 

acres in long-term conserving cover. Acres enrolled in the General Signup of the Conservation Reserve Program 

(CRP) were used to represent land in long-term conserving cover. 

A simulation model was used to estimate the effects of conservation practices that were in use during the period 

2003 to 2006. The National Resources Inventory, a statistical survey of conditions and trends in soil, water, and 

related resources on U.S. non-Federal land conducted by USDA’s Natural Resources Conservation Service, provides 

the statistical framework. Information on farming activities and conservation practices was obtained from a farmer 

survey and other sources. Using those data, conservation practice effects were evaluated in terms of— 

 reductions in losses of sediment, nutrients, and pesticides from 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 

simulate 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 are held constant in the two model runs. 

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. 

The Baseline Conservation Condition 

The first Federal conservation efforts on cropland were focused primarily on water management and soil erosion 

control. Structural practices such as waterways, terraces, and diversions were installed along with supporting 

practices such as contour farming and stripcropping. Conservation tillage emerged in the 1960s and 1970s as a key 

management practice for enhancing soil quality and further reducing soil erosion. The conservation compliance 

provisions in the 1985 Farm Bill sharpened the focus to treatment of the most erodible acres—highly erodible land. 

This legislation created the CRP as a mechanism for establishing long-term conserving cover on the most erodible 

cropland through multi-year contracts with landowners. More recently, the focus has shifted from soil conservation 

and sustainability to a broader goal of reducing all pollution impacts associated with agricultural production. 

Prominent among new concerns are the environmental effects of nutrient and pesticide export from farm fields. 

The application of conservation practices in the UMRB closely reflects this history of Federal conservation 

programs and technical assistance. An assessment of the extent of conservation practice use in the UMRB for the 

period 2003–06, representing the “baseline conservation condition,” found the following: 

 Structural practices for controlling water erosion are in use on 45 percent of UMRB cropped acres, including 72 

percent of the highly erodible land. 

 About 71 percent of the acres meet tillage intensity criteria for no-till or mulch till and are gaining soil organic 

carbon. All but 5 percent of the acres have evidence of some kind of reduced tillage on at least one crop in the 

rotation. 

 Producers use residue and tillage management practices, structural practices, or both, on nearly all of the acres 

in the region. 

 Appropriate rates of nitrogen application are in use on about 34 percent of the acres for all crops in the rotation. 

 Good nitrogen management practices (rate, timing, and method) are in use on about 14 percent of the acres for 

all crops during every year of production. 
Draft June 2010 Page 8 

 Good phosphorus management practices are in use on 29 percent of the acres for all crops during every year of 

production. 

 While most acres have evidence of some nitrogen or phosphorus management, the majority of the acres in the 

region lack consistent use of appropriate rates and timing and method of application, including nearly all of the 

acres receiving manure. 

 Land in long-term conserving cover, as represented by enrollment in the CRP General Signup, consists of 2.8 

million acres in the region, of which 67 percent are highly erodible land. 

Effects of Conservation Practices for the Baseline Conservation Condition 

Model simulation results show that, for cropped acres in the region, on average conservation practices have— 

 reduced surface water flow from farm fields by 16 percent, re-routing the water to subsurface flow pathways; 

 reduced sediment loss from fields by 69 percent; 

 reduced total nitrogen loss (volatilization, denitrification, surface runoff, and subsurface flow losses) from fields 

by 18 percent: 

o reduced nitrogen lost with surface runoff (attached to sediment and in solution) by 46 percent, 

o but only reduced nitrogen loss in subsurface flow by 5 percent; 

 reduced total phosphorus loss from fields by 49 percent; 

 reduced pesticide loss from fields to surface water, resulting in a 51-percent reduction in edge-of-field pesticide 

risk for aquatic ecosystems and a 48-percent reduction in edge-of-field pesticide risk for humans (all pesticides 

combined); and 

 decreased the percentage of acres that are losing soil organic carbon from 41 percent to 25 percent. 

The increase in nitrogen loss in subsurface flow results from a combination of incomplete nutrient management and 

the re-routing of surface water runoff to subsurface flow by water erosion control practices. Structural erosion 

control practices, residue management practices, and reduced tillage slow the flow of surface water runoff and allow 

more of the water to infiltrate into the soil. This re-routing of surface water to subsurface flow not only re-directs the 

dissolved nitrogen into subsurface flow but also can extract additional nitrogen from the soil as the water passes 

through the soil profile. On about 20 percent of the acres in this region, the re-routing of surface water runoff to 

subsurface flow pathways results in sufficient amounts of additional nitrogen being leached from the soil to more 

than offset the reductions in nitrogen lost with surface runoff and produce a small net increase in total nitrogen loss. 

Model simulation of additional conservation treatment shows that pairing effective nutrient management practices 

(consistent use of proper rate, form, timing, and method of application) with water erosion control practices reduces 

nitrogen loss in subsurface flow to acceptable levels for nearly all acres in the region. 

For land in long-term conserving cover, soil erosion and sediment loss have been almost completely eliminated 

compared to a cropped condition without conservation practices, total nitrogen loss has been reduced by 81 percent, 

total phosphorus loss has been reduced by 97 percent, and soil organic carbon has been increased by an average of 

more than 400 pounds per acre. 

These reductions in field-level losses due to conservation practices, including land in long-term conserving cover, 

translate into improvements in water quality in streams and rivers in the region. Transport of sediment, nutrients, 

and pesticides from farm fields to streams and rivers involves a variety of processes and time-lags, and not all of the 

potential pollutants leaving fields contribute to instream loads. Model simulations show that at the outlet of the 

UMRB (Grafton, IL), use of conservation practices has— 

 reduced instream sediment loads by 37 percent; 

 reduced instream nitrogen loads by 21 percent; 

 reduced instream phosphorus loads by 40 percent; and 

 reduced instream atrazine loads by 51 percent. 

If the current level of conservation practice use is not maintained, some of these gains in water quality will be lost. 

 
Draft June 2010 Page 9 

Evaluation of Conservation Treatment Needs 

This study also determined that the combination of practices in use was often inadequate to address excessive losses 

of sediment and nutrients. 

Adequate conservation treatment consists of combinations of conservation practices that treat the specific inherent 

vulnerability factors associated with each field for both sediment and nutrient loss. Not all acres require the same 

level of conservation treatment because of differences in climate and inherent soil vulnerabilities. The evaluation of 

conservation treatment needs was conducted by identifying acres that were inadequately treated with respect to the 

soil runoff or soil leaching potential. 

The evaluation of treatment needs for the UMRB determined that— 

 36 million acres (62 percent of cropped acres) are under-treated for one or more of sediment loss, nitrogen or 

phosphorus lost with surface runoff, and nitrogen or phosphorus loss in subsurface flow: 

o all acres require additional treatment for either nitrogen or phosphorus loss, 

o 58 percent of these acres require additional treatment only for nitrogen loss in subsurface flow, 

o 17 percent require additional treatment for sediment loss, nitrogen runoff, and phosphorus runoff; 

 Of the 36 million under-treated acres, 8.5 million acres (15 percent of cropped acres) are “critical” under-treated 

acres that consist of the most vulnerable acres in the region, most of which require treatment for multiple 

resource concerns; and 

 22 million acres (38 percent) are adequately treated relative to their degree of vulnerability. 

Conservation treatment needs for further reducing the loss of pesticide residues were not estimated. 

Simulation of Additional Conservation Treatment 

Additional conservation treatment was simulated for (1) the 8.5 million most vulnerable under-treated acres in the 

region, and (2) all 36 million under-treated acres. Two levels of treatment were simulated for each set of acres: 

 Treatment with additional erosion control practices, which consisted of adding in-field practices to control 

overland flow (terraces, contouring, or stripcropping) for acres without overland flow control practices and 

having a slope of more than 2 percent, and adding edge-of-field buffering or filtering practices to all acres 

without edge-of-field practices. 

 Treatment with nutrient management in addition to erosion control practices, which was modeled by adjusting 

the commercial fertilizer and manure applications to simulate the appropriate rate of application, the appropriate 

timing of application, and use of the appropriate application method. 

Model simulation demonstrated that sediment and nutrient losses with surface runoff could be effectively controlled 

in the region by treating the 8.5 million most vulnerable under-treated acres with additional erosion control 

practices. At this level of treatment, model simulations showed the following for the region as a whole: 

 Sediment loss from farm fields would average 0.6 ton per acre per year, compared to the baseline conservation 

condition average of 1.0 ton per acre per year (a 40-percent reduction). 

 Nitrogen lost from the field with surface runoff (attached to sediment and in solution) would average 6.1 pounds 

per acre per year, compared to the baseline conservation condition average of 8.6 pounds per acre per year (a 

29-percent reduction). 

 Total phosphorus loss, most of which is lost with surface runoff, would average 2.4 pounds per acre per year, 

compared to 3.0 pounds per acre per year for the baseline conservation condition (a 22-percent reduction). 

However, model simulations also showed that a portion of these nutrient savings was re-routed to subsurface loss 

pathways, most of which is eventually delivered to lakes, streams, and rivers through seepage, artificial drainage 

systems, and groundwater return flow in this region. 

Treatment with nutrient management practices in addition to soil erosion control practices is required to effectively 

control the loss of soluble nitrogen and phosphorus from farm fields in the UMRB. Treatment at this level of all 36 

million under-treated acres, compared to the baseline conservation condition, for the region as a whole would reduce 

nitrogen loss in subsurface flow from an average of 21.8 pounds per acre to an average of 11.4 pounds per acre (a 

48-percent reduction). Total nitrogen loss (all loss pathways) would be reduced 43 percent. Total phosphorus loss 
Draft June 2010 Page 10 

would be reduced to about 1.5 pounds per acre per year, on average, representing a 51-percent reduction from the 

baseline conservation condition. 

Model simulations further showed that the additional reductions in field-level losses would be expected to provide 

the following improvements in water quality at the outlet of the UMRB (Grafton, IL), compared to the baseline 

conservation condition. 

Percent reductions of instream loads at the outlet of the Upper Mississippi River Basin 

due to additional erosion control and nutrient management 

Environmental outcome 

Treatment of the 8.5 million 

most vulnerable under-treated 

acres 

Treatment of all 36 million 

under-treated acres 

Sediment reduction 11% 21% 

Nitrogen reduction 12% 44% 

Phosphorus reduction 12% 27% 

Atrazine reduction 6% 18% 

The nutrient management treatment level simulated in this study represents feasible and proven conservation 

practices that can be successfully applied using today’s technology. There are, however, emerging conservation 

technologies that have the potential to further reduce nutrient loss from farm fields and provide even greater 

conservation benefits once the technologies become more widespread. These include— 

 variable rate technology for precise nutrient application rates and placement methods; 

 nitrogen use efficiency enhancers (time release and ammonia loss inhibitors); 

 water control management which reduces late fall and early spring flushes of nitrate-laden drainage water; and 

 constructed wetlands that receive surface water runoff from fields prior to discharge to streams and rivers. 

Not all acres get the same benefit from conservation treatment. The more vulnerable acres, such as highly erodible 

land and soils prone to leaching, inherently lose more sediment and/or nutrients, and therefore greater benefit can be 

attained with conservation treatment. The gains in efficiency by treating the more vulnerable acres first are 

demonstrated in the table below using results from the treatment simulations: 

Average annual per-acre reductions in loss from treatment of designated acres 

with additional erosion control and nutrient management 

Resource concern 

8.5 million critical 

under-treated acres 

27.5 million noncritical under-treated 

acres 

Remaining 22.2 

million acres 

Sediment loss at edge of field due 

to water erosion (tons/acre) 2.7 0.7 0.5 

Total nitrogen loss for all pathways 

(pounds/acre) 39 25 9 

Loss of nitrogen with surface 

runoff, including waterborne 

sediment (pounds/acre) 17 6 4 

Loss of nitrogen in subsurface 

flows (pounds/acre) 18 16 3 

Total phosphorus loss for all 

pathways (pounds/acre) 4.6 1.8 1.3 

Diminishing returns to additional conservation treatment are pronounced for sediment, phosphorus, and nitrogen lost 

with surface runoff. For nitrogen loss in subsurface flow, however, diminishing returns are not evident until all the 

under-treated acres are treated, a reflection of the pervasiveness of the nitrogen leaching problem in this region. 

 

 
Draft June 2010 Page 11 

Conclusions 

The results of the study lead to the following conclusions for the UMRB: 

 Conservation practice adoption has made good progress toward reducing sediment, nutrient, and pesticide 

losses from farm fields, but significant challenges remain. 

o Erosion control practices are widespread, but some of the more vulnerable acres are not adequately treated 

for erosion and sediment loss. 

o Nutrient management practices are common, but they do not consistently meet criteria for appropriate 

application rate and method and timing for all crops in all years of the crop rotation. 

o Acres receiving manure applications consistently have higher nutrient losses than do acres not receiving 

manure. Acres where manure is applied require more intensive and comprehensive treatment to attain 

acceptable levels of nutrient loss than do acres where manure is not applied. 

 About 38 percent of the acres are adequately treated for sediment, nitrogen, and phosphorus loss. However, 

about 62 percent of the acres still require additional conservation treatment to reduce sediment and/or nutrient 

losses to acceptable levels. The majority require additional treatment only for nitrogen leaching. About 15 

percent of the cropped acres are “critical under-treated” acres, most of which require additional conservation 

treatment for multiple resource concerns. 

 Model simulations showed that adequate treatment for all resource concerns was rarely achieved with single 

practice solutions. Full treatment of the most vulnerable acres will require a suite of conservation practices 

designed to— 

o avoid or limit the potential for loss by consistently using nutrient management practices (appropriate rate, 

form, method, and timing) on all crops in the rotation; 

o control overland flow and concentrated flow; and 

o trap materials leaving the field using appropriate edge-of-field mitigation. 

 Nutrient management is especially important for acres with erosion control treatment because some of the 

surface water that carries nitrogen and phosphorus in solution is re-routed to subsurface loss pathways, where it 

is more difficult to treat. A significant portion of these nutrients carried in subsurface flows is eventually 

delivered to lakes, streams, and rivers through seepage, artificial drainage systems, and groundwater return 

flow. 

 Simulation of additional conservation treatment indicated that, by augmenting conservation practices already in 

use with needed improvements in nutrient management on under-treated acres in the region, nitrogen savings 

could be more than doubled with respect to savings already attained. 

 Even when fully treated, however, some of the most vulnerable acres will have unacceptable losses, especially 

during years with extreme weather events. For these acres, a change in the cropping system, land use change, or 

establishment of long-term conserving cover may be necessary to meet watershed protection goals.

 
Draft June 2010 Page 12 

Potential for Using Model Simulation to Assess 

Alternative Conservation Policy Options 

The models and databases used in this study to assess the effects of conservation practices are uniquely 

capable of being used to simulate a variety of alternative policy options and answers “what if” 

questions. The simulation models incorporate a large amount of natural resource and management data 

and account for the physical processes that determine the fate and transport of soil, nutrients, and 

pesticides. What is new and innovative about the CEAP-Cropland model simulations is that the 

farming activities represented at each of the individual sample points are based on actual farming 

activities that are consistent with the specific natural resource conditions at each sample point—

climate, soil properties, and field characteristics—thus accounting for the diversity of farming 

operation activities and natural conditions that exist in the “real world.” Moreover, the field-level 

model results are linked to a regional water quality model that provides a direct connection between 

activities at the farm field level and offsite water quality outcomes. 

While many of the results in this report have implications for policy questions, the primary purpose of 

the study was to assess the effects of conservation practices. Separate model simulations and scenarios 

that account for the specific goals of policy would need to be constructed to appropriately address 

other policy-related issues. Examples of conservation policy issues that could be further explored with 

the CEAP cropland modeling system include— 

 simulation of additional conservation treatment required to meet specific water quality goals, 

including the extent to which conservation treatment can be used to meet nitrogen and 

phosphorus reduction goals for the region; 

 assessment of the impact of climate change on the performance of existing conservation 

practices and additional conservation treatment required to maintain the level of water quality 

in future years; 

 determination of the number and kind of acres that would provide the most cost-effective 

approach to meeting regional conservation program goals, given constraints in budget and 

staff; 

 experimentation with alternatives for new conservation initiatives and the environmental 

benefits that could be attained; 

 simulation of proposed rules for carbon or nutrient trading; evaluation of potential future 

options for Conservation Reserve Program (CRP) enrollments, including identification of the 

number and kind of acres that would provide the maximum water quality protection; and 

 evaluation and assessment of treatment alternatives for specific environmental issues, such as 

treatment alternatives for tile-drained acres, treatment alternatives for acres receiving manure, 

or treatment alternatives to reduce soluble nutrient loss. 
Draft June 2010 Page 13 

Chapter 1 

Land Use and Agriculture in the 

Upper Mississippi River Basin 

Land use 

The Upper Mississippi River Basin (UMRB) covers some 

190,000 square miles between Lake Itasca in northern 

Minnesota and the confluence of the Mississippi and Ohio 

Rivers at the southern tip of Illinois. The basin includes large 

parts of Illinois, Iowa, Minnesota, Missouri, and Wisconsin, 

and small areas in Indiana, Michigan, and South Dakota. 

About half the area of the UMRB is used for crop production 

(table 1 and figure 1). About 16 percent of the Nation’s 

cropland is in the UMRB. The highest concentrations of 

cropland are in northeastern and central Iowa and southern 

Minnesota, where cropland makes up more than 80 percent of 

the land in some counties. 

The second most common land cover in the UMRB is forest 

land, which covers about one-fourth of the basin, mostly in the 

north. The forests consist primarily of deciduous trees with 

conifers and mixed stands in some areas. 

Pastureland and hayland make up about 8 percent of the land 

cover in the region. 

Urban areas make up about 8 percent of the basin. The major 

metropolitan areas are Chicago, IL; Minneapolis-St. Paul, 

MN; St. Louis, MO; Des Moines, IA; and the Quad Cities area 

of Illinois and Iowa. 

Agriculture 

The 2007 Census of Agriculture reported about 279,000 farms 

in the UMRB, about 13 percent of the total number of farms in 

the United States (table 2) Farms in the UMRB make up about 

9 percent of all farmland in the nation. 

According to the 2007 Census of Agriculture, the value of 

UMRB agricultural sales in 2002 was about $44 billion—57 

percent from crops and 43 percent from livestock. About 66 

percent of UMRB farms primarily raise crops, about 25 

percent are primarily livestock operations, and the remaining 9 

percent produce a mix of livestock and crops (table 3). 

The majority of farms (59 percent) in 2007 were small 

operations with less than $50,000 in total farm sales. About 12 

percent of the farms had total farm sales greater than $500,000 

(table 3). 

Thirty-two percent of the farms in the UMRB are smaller than 

50 acres, 52 percent are between 50 and 500 acres, and 14 

percent are from 500 to 2,000 acres. Only about 2 percent of 

the farms in the region are operations with more than 2,000 

acres (table 3). 

Crop production 

The UMRB accounts for about 17 percent of all U.S. crop 

sales, including 30 percent of U.S. sales of grains and oilseeds 

(table 2). Corn and soybeans are the principal crops grown. 

Wheat and alfalfa hay are important secondary crops. 

Farmers in the region produced 41 percent of all corn 

harvested for grain in the United States in 2007—5.2 billion 

bushels—on about 32 million acres. They also produced 34 

percent of the national soybean crop (0.9 billion bushels) on 

19 million acres. 

Commercial fertilizers and pesticides are widely used 

throughout the region (table 2). In 2007, 47 million acres of 

cropland were fertilized, 47 million acres of cropland and 

pasture were treated with chemicals for weed control, and 20 

million acres of cropland were treated for insect control. 

About 5.3 million acres had manure applied in 2007. 

Irrigation use is uncommon in the UMRB. Only about 2 

percent of the harvested acres were irrigated in 2007.

Livestock operations 

Livestock production in the region is dominated by swine 

operations, followed by dairy. Livestock operations in the 

region produced 35 percent of all hog and pig sales in the 

United States in 2007, exceeding $6 billion in value (table 2). 

Sales of dairy products ranked second in the region at $5 

billion, representing 17 percent of the U.S. total. Beef 

production is also important in the region. The region 

accounted for about 11 percent of cattle on feed in the United 

States in 2007. 

Although about half of the farms in the UMRB reported 

livestock sales in 2007, the majority are small operations. 

About 55,000 farms had fewer than 30 animal units1

 on the 

farm; a small number of these had specialty livestock such as 

rabbits, bison, mink, or deer (table 3). Pastured livestock 

(cattle, horses, sheep, or goats) predominate on about 35,000 

farms; 90 percent of these farms raised fewer than 100 animal 

units. About 45,000 farms could be defined as animal feeding 

operations (AFOs). AFOs are typically livestock operations 

with confined livestock, such as poultry, swine, cattle on feed, 

or dairies. Sixteen percent of the farms in the UMRB are 

AFOs, although the bulk of these are relatively small 

operations. Only about 2,730 of the livestock operations (6 

percent of the AFOs) are large, with livestock numbers above 

the threshold for a Concentrated Animal Feeding Operation 

(CAFO). 

 

 

1

 An animal unit is 1,000 pounds of live animal weight. 
Draft June 2010 Page 14 

Watersheds 

A hydrologic accounting system consisting of water resource 

regions, major subbasins, and smaller watersheds has been 

defined by the U.S. Geological Survey (USGS) (1980). The 

UMRB is one of the 18 water resource regions in the 

conterminous United States. Each water resource region is 

designated with a 2-digit code, which is further divided into 4-

digit subbasins and then into 8-digit watersheds, or Hydrologic 

Unit Catalogs (HUCs). For example, in the UMRB the 8-digit 

watershed “07110009” belongs to the “07” 2-digit basin and 

the “0711” 4-digit subbasin. 

The 14 subasins within the UMRB are shown in figure 2, and 

agricultural land use within each subbasin is summarized in 

table 4. Cultivated cropland is the dominant land use in all but 

four northern subbasins and the southernmost subbasin. About 

half of the cultivated cropland in the UMRB is found in four 

subbasins: 

 Upper Mississippi-Iowa-Skunk-Wapsipinicon (subbasin 

code 0708) 

 Minnesota River Basin (subbasin code 0702) 

 Lower Illinois River Basin (subbasin code 0713) 

 Des Moines River Basin (subbasin code 0710) 

In each of these four subbasins, more than 70 percent of the 

landscape is cultivated cropland. This region of concentrated 

cultivated cropland extends through the central portion of the 

basin, as shown in figures 1 and 2. Pastureland, hayland, and 

woodland are more prominent land covers in the northern and 

southern subbasins. 
Draft June 2010 Page 15 

Table 1. Distribution of land cover in the Upper Mississippi River Basin

Land use Acres* Percent 

Cultivated cropland and land enrolled in the CRP General Signup 63,512,000 52 

Forest deciduous 22,203,000 18 

Hay/Pasture not in rotation with crops 10,118,000 8 

Urban 9,965,000 8 

Water 3,339,000 3 

Wetland forested 3,307,000 3 

Range grasses 2,994,000 2 

Wetland non-forested 2,643,000 2 

Forest evergreen 1,672,000 1 

Forest mixed 969,000 1 

Range brush 621,000 1 

Horticulture and barren 158,000 <1 

 Total 121,501,000 100 

SOURCE: 2001 National Land Cover Data (NLCD) (US EPA, 2007) and the 1997 National Resources Inventory 

*Acreage estimates for cultivated cropland differ slightly from those provided elsewhere in this report because of differences in sources.

Figure 1. Land cover in the Upper Mississippi River Basin 

SOURCE: 2001 National Land Cover Data (NLCD) (US EPA, 2007)
Draft June 2010 Page 16 

Table 2. Profile of farms in the Upper Mississippi River Basin, 2007 

Characteristic Value 

Percent of national 

total 

Number of farms 278,687 13 

Acres on farms 80,748,559 9 

Average acres per farm 290 

Cropland harvested, acres 59,369,843 19 

Cropland used for pasture, acres 1,866,087 5 

Cropland on which all crops failed, acres 199,293 3 

Cropland in summer fallow, acres 114,569 1 

Cropland idle or used for cover crops, acres 3,484,935 9 

Woodland pastured, acres 1,716,667 6 

Woodland not pastured, acres 5,039,206 11 

Permanent pasture and rangeland, acres 5,117,665 1 

Other land on farms, acres 3,840,294 12 

Total acres 80,748,559 9 

Principal crops grown 

 Field corn for grain harvested, acres 31,852,104 37 

 Field corn for silage harvested, acres 1,081,711 18 

 Soybeans harvested, acres 19,283,549 30 

 Wheat harvested, sum acres 1,354,073 3 

 Alfalfa hay harvested, acres 2,767,896 14 

Irrigated harvested land, acres 1,364,944 3 

Irrigated pastureland or rangeland, acres 12,650 <1 

Cropland fertilized, acres 46,981,154 19 

Pastureland fertilized, acres 1,247,434 5 

Land treated for insects on hay or other crops, acres 19,616,465 22 

Land treated for nematodes in crops, acres 1,643,590 22 

Land treated for diseases in crops and orchards, acres 2,581,415 11 

Land treated for weeds in crops and pasture, acres 46,529,531 21 

Crops on which chemicals for defoliation applied, acres 154,525 1 

Acres on which manure was applied 5,297,994 24 

Total grains and oilseeds sales, million dollars 22,870 30 

Total fruit and berry sales, million dollars 239 1 

Total vegetable, melons sales, million dollars 632 4 

Total nursery, greenhouse, and floriculture sales, million dollars 890 5 

Total crop sales, million dollars 25,097 17 

Total dairy sales, million dollars 5,308 17 

Total hog and pigs sales, million dollars 6,239 35 

Total poultry and eggs sales, million dollars 2,188 6 

Total cattle sales, million dollars 4,892 8 

Total sheep, goats, and their products sales, million dollars 61 9 

Total horses, ponies, and mules sales, million dollars 49 2 

Total livestock sales, million dollars 18,962 12 

Total crop and livestock sales, million dollars 44,059 15 

Animal units on farms 

 All livestock types 11,597,113 11 

Swine 3,604,576 35 

Dairy cows 2,136,316 17 

Fattened cattle 1,400,287 11 

Other cattle, horses, sheep, goats 2,974,834 6 

Turkeys 436,172 19 

Source: 2007 Census of Agriculture, National Agricultural Statistics Service, USDA 

Note: Information in the Census of Agriculture was used to estimate animal units using methods and assumptions described in USDA-NRCS (2003). 

 
Draft June 2010 Page 17 

Table 3. Characteristics of farms in the Upper Mississippi River Basin, 2007 

Number of 

farms 

Percent of 

farms in 

UMRB 

Farming primary occupation 135,688 49 

Farm size: 

<50 acres 88,987 32 

50–500 acres 145,408 52 

500–2,000 acres 39,814 14 

>2,000 acres 4,478 2 

Farm sales: 

<$10,000 120,763 43 

$10,000–50,000 45,195 16 

$50,000–250,000 54,422 20 

$250,000–500,000 25,075 9 

>$500,000 33,232 12 

Farm type: 

Crop sales make up more than 75% of farm sales 184,653 66 

Livestock sales make up more than 75% of farm sales 69,224 25 

Mixed crop and livestock sales 24,810 9 

Farms with no livestock sales 143,046 51 

Farms with few livestock or specialty livestock types 55,333 20 

Farms with pastured livestock and few other livestock types 35,150 13 

Farms with animal feeding operations (AFOs)* 45,158 16 

Source: 2007 Census of Agriculture, National Agricultural Statistics Service, USDA 

* AFOs, as defined here, typically have a total of more than 12 animal units consisting of fattened cattle, dairy cows, hogs and pigs, chickens, ducks, and turkeys. 

 
Draft June 2010 Page 18 

Figure 2. Percent cultivated cropland, including land in long-term conserving cover, for the 14 subbasins in the Upper Mississippi 

River Basin

Table 4. Agricultural land use in the 14 subbasins in the Upper Mississippi River Basin (UMRB) 

Subbasin 

code Subbasin name 

Cultivated 

cropland 

(1,000 

acres)* 

Percent of 

cultivated 

cropland 

acres in 

long-term 

conserving 

cover 

Pastureland 

not in 

rotation 

with crops 

(1,000 

acres) 

Hayland 

not in 

rotation 

with 

crops 

(1,000 

acres) 

Total 

agricultural 

land (1,000 

acres) 

Percent 

cultivated 

cropland 

in 

subbasin 

Percent 

of 

cultivated 

cropland 

in UMRB 

0701 Mississippi Headwaters 3,102 6.0 659 851 12,904 24.0 5.0 

0702 Minnesota River Basin 8,290 4.3 239 166 10,802 76.7 13.2 

0703 St. Croix River Basin 629 7.2 230 408 4,950 12.7 1.0 

0704 Upper Mississippi-Black-Root 3,271 7.9 485 6 6,880 47.5 5.2 

0705 Chippewa River Basin 1,385 3.6 233 0 6,109 22.7 2.2 

0706 Upper Mississippi-MaquoketaPlum 2,999 10.9 396 345 5,489 54.6 4.8 

0707 Wisconsin River Basin 2,393 6.2 258 1 7,633 31.3 3.8 

0708 Upper Mississippi-Iowa-SkunkWapsipinicon 10,773 5.3 406 462 14,673 73.4 17.2 

0709 Rock River Basin 4,663 4.4 406 293 7,005 66.6 7.4 

0710 Des Moines River Basin 6,578 5.3 277 624 9,265 71.0 10.5 

0711 Upper Mississippi-Salt 2,967 15.4 365 1,062 6,445 46.0 4.7 

0712 Upper Illinois River Basin 4,062 0.9 97 105 6,979 58.2 6.5 

0713 Lower Illinois River Basin 8,064 1.5 153 471 11,456 70.4 12.9 

0714 Upper Mississippi-KaskaskiaMeramec 3,471 6.6 459 1,355 10,912 31.8 5.5 

 Total 62,647 5.4 4,662 6,148 121,501 51.6 100.0 

* Acres of cultivated cropland include land in long-term conserving cover. 

Note: Estimates in this table were obtained from HUMUS databases on land use, and do not exactly match the acreage estimates obtained from the NRI-CEAP sample. 
Draft June 2010 Page 19 

Chapter 2 

Modeling the Effects of Conservation 

Practices 

Scope of Study 

This report provides estimates for the Upper Mississippi River 

Basin (UMRB) of— 

 environmental benefits and effects of conservation 

practices in use in the Upper Mississippi River Basin; 

 conservation treatment needs for the region; and 

 potential gains that could be attained with additional 

conservation treatment. 

The study was designed to quantify at the regional level the 

effects of commonly used conservation practices on cultivated 

cropland, regardless of how or why the practices came to be in 

use. This assessment is not an evaluation of Federal 

conservation programs, because it is not restricted to only 

those practices associated with Federal conservation programs. 

For purposes of this report, cultivated cropland includes land 

in row crops or close-grown crops, hay and pasture in rotation 

with row crops and close-grown crops, and land in long-term 

conserving cover. Cultivated cropland does not include 

agricultural land that has been in hay, pasture, or horticulture 

for the most recent 4 years. Acres enrolled in the General 

Signup of the Conservation Reserve Program (CRP) were 

used to represent cultivated cropland currently in long-term 

conserving cover. The UMRB has about 61 million acres of 

cultivated cropland—58 million cropped acres and about 3 

million acres in long-term conserving cover. 

Overview of Sampling and Modeling 

Approach

The assessment uses a statistical sampling and modeling 

approach to estimate the environmental effects and benefits of 

conservation practices (figure 3). 

 A subset of 3,703 National Resources Inventory (NRI) 

sample points provides a statistical sample that represents 

the diversity of soils and other conditions for cropped 

acres in the UMRB. The sample also includes 1,831 

additional NRI sample points designated as CRP acres to 

represent land in long-term conserving cover. NRI sample 

points are linked to NRCS Soil Survey databases and 

were linked spatially to climate databases for this study. 

 A farmer survey—the NRI-CEAP Cropland Survey—was 

conducted at these sample points during the period 2003–

06 to determine what conservation practices were in use 

and to collect information on farming practices. 

 The field-level effects of the conservation practices were 

assessed using a field-scale physical process model—the 

Agricultural Policy Environmental Extender (APEX)—

which simulates the day-to-day farming activities, wind 

and water erosion, loss or gain of soil organic carbon, and 

edge-of-field losses of soil, nutrients, and pesticides. 

 A watershed model and system of databases—the 

Hydrologic Unit Model for the United States 

(HUMUS)—was then used to simulate how reductions of 

field losses have reduced instream concentrations and 

loadings of sediment, nutrients, and pesticides within the 

UMRB. The SWAT model (Soil and Water Assessment 

Tool) was used to simulate nonpoint source loadings from 

noncultivated cropland sources and to route instream 

loads from one watershed to another. 

Figure 3. Statistical sampling and modeling approach used to simulate the effects of conservation practices 
Draft June 2010 Page 20 

The modeling strategy for estimating the effects of 

conservation practices consists of two model scenarios that are 

produced for each sample point. 

1. A baseline scenario, the “baseline conservation condition” 

scenario, provides model simulations that account for 

cropping patterns, farming activities, and conservation 

practices as reported in the NRI-CEAP Cropland Survey 

and other sources. 

2. An alternative scenario, the “no-practice” scenario, 

simulates model results as if no conservation practices 

were in use but holds all other model inputs and 

parameters the same as in the current conservation 

condition scenario.

The effects of conservation practices are obtained by taking 

the difference in model results between the two scenarios 

(figure 4).2

 For example, to simulate “no practices” for sample 

points where some type of residue management is used, model 

simulations were conducted as if continuous conventional 

tillage had been used. Similarly, for sample points with 

structural conservation practices (buffers, terraces, grassed 

waterways, etc.), the no-practice scenario was simulated as if 

the practices were not present. The no-practice representation 

for land in long-term conserving cover was derived from 

model results for cropped acres as simulated in the no-practice 

scenario, representing how the land would have been managed 

had crops been grown without the use of conservation 

practices. 

The approach captures the diversity of land use, soils, climate, 

and topography from the NRI; 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 national and 

regional levels. 

The NRI and the CEAP subsample 

The approach is an extension of the NRI, a longitudinal, 

scientifically-based survey designed to gauge natural resource 

status, conditions, and trends on the Nation’s non-Federal land 

(Goebel 1998; USDA-NRCS 2002). NRCS has previously 

used the NRI for modeling to address issues related to natural 

resources and agriculture (Goebel and Kellogg 2002).3

 

 

2

 This modeling strategy is similar to how the NRI produces estimates of soil 

erosion and the intrinsic erosion rate used to identify highly erodible land. The 

NRI uses the Universal Soil Loss Equation (USLE) to estimate sheet and rill 

erosion at each sample point on the basis of site-specific factors. Soil loss per 

unit area is equal to R*K*L*S*C*P. The first four factors—R, K, L, S—

represent the conditions of climate, soil, and topography existing at a site. 

(USDA-NRCS 1989). The last two factors—C and P—represent the degree to 

which management influences the erosion rate. The product of the first four 

factors is sometimes called the intrinsic, or potential, erosion rate. The 

intrinsic erosion rate divided by T, the soil loss tolerance factor, produces 

estimates of EI, the erodibility index. The intrinsic erosion rate is thus a “nopractice” representation of sheet and rill erosion, since C=1 represents 

smooth-tilled continuous fallow and P=1 represents no supporting practices. 3

 Previous studies have used this NRI micro-simulation modeling approach to 

estimate soil loss, nutrient loss, and change in soil organic carbon (Potter et al. 

2006), to estimate pesticide loss from cropland (Kellogg et al. 1992, 1994, 

2002; Goss et al. 1998), and to identify priority watersheds for water quality 

protection from nonpoint sources related to agriculture (Kellogg 2000, 

Kellogg et al. 1997). 

Figure 4. Modeling strategy used to assess effects of 

conservation practices 

The NRI sampling design implemented in 1982 provided a 

stratified, two-stage, unequal probability area sample of the 

entire country (Goebel and Baker 1987; Nusser and Goebel 

1997). Nominally square areas/segments were selected within 

geographical strata on a county-by-county basis; specific point 

locations were selected within each selected segment. The 

segments ranged in size from 40 to 640 acres but were 

typically half-mile square areas, and most segments contained 

three sample points. At each sample point, information is 

collected on nearly 200 attributes; some items are also 

collected for the entire segment. The sampling rates for the 

segments were variable, typically from 2 to 6 percent in 

agricultural strata and much lower in remote nonagricultural 

areas. The 1997 NRI Foundation Sample contained about 

300,000 sample segments and about 800,000 sample points. 

NRCS made several significant changes to the NRI program 

over the past 10 years, including transitioning from a 5-year 

periodic survey to an annual survey. The NRI’s annual design 

is a supplemented panel design. A core panel of 41,000 

segments is sampled each year, and rotation (supplemental) 

panels of 31,000 segments each vary by inventory year and 

allow an inventory to focus on an emerging issue. The core 

panel and the various supplemental panels are unequal 

probability subsamples from the 1997 NRI Foundation 

Sample.4

 

 

4

 For more information on the NRI, see www.nrcs.usda.gov/technical/NRI/. 
Draft June 2010 Page 21 

The 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.5

 The sample is statistically representative of 

cultivated cropland and formerly cultivated land currently in 

long-term conserving cover. Nationally, the NRI-CEAP 

sample consists of about 18,700 NRI points representing 

cropped acres,6

 and about 13,000 NRI points representing land 

enrolled in the General Signup of the CRP. 

The UMRB portion of the NRI-CEAP sample consists of 

3,703 sample points representing 58.2 million cropped acres 

and 1,831 sample points representing 2.8 million acres of 

agricultural land in long-term conserving cover. Table 5 

provides a breakdown of sample sizes for the dominant 

cropping systems that occur in the UMRB. 

Table 5. Cultivated cropland in the UMRB

Cropping System 

Number 

of 

CEAP 

samples 

Estimated 

acres 

Percent

of acres

Corn-soybean only 2,694 42,980,688 71 

Corn only 316 5,037,033 8 

Hay-crop mix 237 3,653,031 6 

Corn-soybean with close grown 

crops 164 2,144,046 4 

Soybean only 105 1,507,404 2 

Soybean-wheat only 63 783,464 1 

Corn and close grown crops 41 752,294 1 

Remaining mix of crops 83 1,295,541 2 

Sub-total for cropped acres 3,703 58,153,500 95 

CRP General Signup, representing 

cultivated cropland in long-term 

conserving cover 1,831 2,801,700 5 

Total 5,534 60,955,200 100 

Note: Cultivated cropland acres in this table differ slightly from estimates 

provided elsewhere in this report because of differences in sources. 

Acres reported using the CEAP sample are “estimated” acres 

because of the uncertainty associated with the statistical 

sample. Standard errors for estimated acres used in this report 

are provided in Appendix A. 

The NRI-CEAP Cropland Survey 

A farmer survey—the NRI-CEAP Cropland Survey—was 

conducted to obtain the additional information needed for 

modeling the 3,703 sample points with crops. The USDA 

National Agricultural Statistics Service (NASS) administered 

the survey. Farmer participation was voluntary, and the 

information gathered is confidential. The survey content was 

 

5

 Information about the CEAP sample design is in “NRI-CEAP Cropland 

Survey Design and Statistical Documentation,” available at 

www.nrcs.usda.gov/technical/nri/ceap/umrbdocumentation/. 6

 A completed farmer survey was required to include the sample point in the 

CEAP sample. Some farmers declined to participate in the survey, others 

could not be located during the time period scheduled for implementing the 

survey, and other sample points were excluded for administrative reasons such 

as overlap with other USDA surveys. Some sample points were excluded 

because the surveys were incomplete or contained inconsistent information, 

land use found at the sample point had recently changed and was no longer 

cultivated cropland, or because the crops grown were uncommon and model 

parameters for crop growth were not available. 

specifically designed to provide information on farming 

activities for use with a physical process model to estimate 

field-level effects of conservation practices. The survey 

obtained information on—7

 crops grown for the previous 3 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 the previous 3 years; 

 application of manure (source and type, consistency, 

application rate, method, and timing) on the field over the 

previous 3 years; 

 application of pesticides (chemical, rate, timing, and 

method) for the previous 3 years; 

 pest management practices; 

 irrigation practices (system type, amount, and frequency); 

 timing and equipment used for all field operations (tillage, 

planting, cultivation, harvesting) over the previous 3 

years; 

 practices to improve wildlife habitat and operator’s 

judgment on their effects on local wildlife populations; 

and 

 general characteristics of the operator and the operation. 

Farmers were also asked about the presence of structural 

conservation practices associated with the field. In a separate 

survey, NRCS field offices provided information on the 

practices specified in conservation plans. 

Because of the large size of the sample, it was necessary to 

spread the data collection process over a 4-year period, from 

2003 through 2006. In each year, surveys were obtained for a 

separate set of sample points. The final CEAP sample was 

constructed by pooling the set of usable, completed surveys 

from all four years. 

Farmer responses to the NRI-CEAP Cropland Survey for the 

UMRB are summarized in Appendix B. 

The field-level cropland model—APEX 

A complex physical process model called APEX was used to 

simulate the effects of conservation practices at the field level 

(Williams et al., 2008; Williams et al., 2006; Gassman et al. 

2009 and 2010).8

 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.9

 

7

 The surveys, the enumerator instructions, and other documentation can be 

found at www.nrcs.usda.gov/technical/nri/ceap/surveys.html. 8

 The full theoretical and technical documentation of APEX can be found at 

http://epicapex.brc.tamus.edu/downloads/user-manuals.aspx . 9

 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. 
Draft June 2010 Page 22 

The APEX model is a field-scale, daily time-step model that 

simulates weather, farming operations, crop growth and yield, 

and the movement of water, soil, carbon, nutrients, sediment, 

and pesticides (figure 5). The APEX model and its 

predecessor, EPIC (Environmental Policy Impact Calculator), 

have a long history of use in simulation of agricultural and 

environmental processes and of the effect of agricultural 

technology and government policy (Izaurralde et al., 

2006;Williams, 1990; Williams et al., 1984;Gassman et al. 

2005).10 

Figure 5. Daily hydrologic processes simulated by APEX 

On a daily basis, APEX simulates the farming operations used 

to grow crops, such as planting, tillage before and after 

planting, application of nutrients and pesticides, application of 

manure, irrigation, and harvest. Weather events and their 

interaction with crop cover and soil properties are simulated; 

these events affect crop growth and the fate and transport of 

water and chemicals through the soil profile and over land to 

the edge of the field. Over time, the chemical makeup and 

physical structure of the soil may change, which in turn affect 

crop yields and environmental outcomes. Crop residue 

remaining on the field after harvest is transformed into organic 

matter. Organic matter may build up in the soil over time, or it 

may degrade. 

APEX simulates all of the basic biological, chemical, 

hydrological, and meteorological processes of farming 

systems and their interactions. Soil erosion is simulated over 

time, including 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 their 

availability for plant growth or for transport from the field. 

Exchange of gaseous forms between the soil and the 

atmosphere is simulated, including losses of gaseous nitrogen 

compounds. 

 

10 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/umrbdocumentation/. 

The NRI-CEAP Cropland Survey was the primary source of 

information on all farming activities simulated using APEX. 

Crop data were transformed for the model into a crop rotation 

for each sample point, which was then repeated over the 47-

year simulation. The 3 years of data reported in the survey 

were represented in the model simulation as 1-, 2-, 3-, 4-, or 5-

year crop rotations. For example, a 2-year corn-soybean 

rotation was used if the operator reported that corn was grown 

in the first year, soybeans in the second year, and corn again in 

the third year. In this case, only 2 of the reported 3 years of 

survey data were used. If management differed significantly 

for the 2 years that corn was grown (manure was applied, for 

example, or tillage was different), the rotation was expanded 

to 4 years, retaining the second year of corn and repeating the 

year of soybeans. In addition, some rotations with alfalfa or 

grass seed were simulated as 5-year rotations. Specific rules 

and procedures were established for using survey data to 

simulate cover crops, double crops, complex systems such as 

intercropping and nurse crops, perennial hay in rotations, 

abandoned crops, re-planting, multiple harvests, manure 

applications, irrigation, and grazing of cropland before and 

after harvest.11 

Use of conservation practices in the UMRB was obtained from 

four sources: (1) NRI-CEAP Cropland Survey, (2) NRCS field 

offices, (3) USDA Farm Service Agency (FSA), and (4) the 

2003 NRI. For each sample point, data from these four sources 

were pooled and duplicate practices discarded.12

The national water quality model—HUMUS/SWAT 

Offsite estimates of water quality benefits were assessed using 

HUMUS/SWAT, a combination of the SWAT model and 

HUMUS (Hydrologic Unit Modeling for the United States) 

databases required to run SWAT at the watershed scale for all 

watersheds in the United States (Arnold et al. 1999; Srinivasan 

et al. 1998). SWAT simulates the transport of water, sediment, 

pesticides, and nutrients from the land to receiving streams 

and routes the flow downstream to the next watershed and 

ultimately to estuaries and oceans (figure 6). 

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).13 The hydrologic cycle in the model is 

divided into two parts. The land phase of the hydrologic cycle, 

or upland processes, simulates the amount of water, sediment, 

nutrients, and pesticides delivered from the land to the outlet 

of each watershed. The routing phase of the hydrologic cycle, 

or channel processes, simulates the movement of water, 

sediment, nutrients, and pesticides from the outlet of the 

upstream watershed through the main channel network to the 

watershed outlet. 

 

11 For a detailed description of the rules and procedures, see “Transforming 

Survey Data to APEX Model Input Files,” 

http://www.nrcs.usda.gov/technical/nri/ceap/umrbdocumentation/. 12 For a detailed description of the rules and procedures for simulation of 

structural conservation practices, see “Modeling Structural Conservation 

Practices in APEX,” 

http://www.nrcs.usda.gov/technical/nri/ceap/umrbdocumentation/. 13 A complete description of the SWAT model can be found at 

http://www.brc.tamus.edu/swat/index.html. 
Draft June 2010 Page 23 

Figure 6. Sources of water flows, sediment, and agricultural 

chemicals simulated with HUMUS/SWAT 

Source loads for cultivated cropland are estimated by APEX, 

and source loads for noncultivated land uses are estimated by 

SWAT. SWAT simulates the fate and transport of water, 

sediment, nutrients, and pesticides for the following land use 

categories, referred to as Hydrologic Response Units (HRUs): 

 Pastureland 

 Range shrub 

 Range grass 

 Urban 

 Mixed forest 

 Deciduous forest 

 Evergreen forest 

 Horticultural lands 

 Forested wetlands 

 Non-forested wetlands 

All source loads, including point sources, are introduced into 

SWAT at the outlet of each watershed (8-digit hydrologic unit 

code [HUC]). Flows and source loads from upstream 

watersheds are routed through each downstream watershed, 

including reservoirs when present. During the routing, channel 

processes such as sediment deposition and degradation and 

nutrient and pesticide transformations are simulated (figure 

7).14

Instream loads of sediment, nitrogen, phosphorus, and the 

pesticide atrazine are reported for each of the 14 subbasins (4-

digit HUC) in the UMRB. Atrazine was the only pesticide 

modeled in the UMRB because of its dominance in 

determining environmental risk in the region.

Simulating weather 

In the UMRB, weather is the predominant factor determining 

the loss of soil, nitrogen, phosphorus, and pesticides from 

farm fields, as well as the effects of conservation practices. 

 

14 For a complete documentation of HUMUS/SWAT as it was used in this 

study, as well as a summary of calibration and validation results for the 

UMRB, see “The CEAP-HUMUS National Water Quality Modeling System 

and Databases” at 

http://www.nrcs.usda.gov/technical/nri/ceap/umrbdocumentation/. 

Figure 7. SWAT model channel simulation processes 

To capture the effects of weather, each scenario was simulated 

for 47 years using actual daily weather data for the time period 

1960 through 2006.15 The same 47-year weather data were 

used in the HUMUS/SWAT simulations that were used in the 

APEX model simulations. 

Annual precipitation over the 47-year simulation averaged 

about 34 inches in this region. However, annual precipitation 

varies substantially in the model simulations, both within the 

region and from year to year, as shown in figure 8. Each curve 

shows how annual precipitation varied over the region in one 

of the 47 years. The family of curves shows the variability 

from year to year. Generally, the drier parts of the region 

receive about half as much rainfall (22 inches on average) as 

the wettest parts of the region (49 inches on average). Year-toyear variability is equally pronounced—the annual median 

precipitation amount (representing the region as a whole) 

ranged from 23 inches per year to 46 inches per year. 

The 5 driest years included in the model simulation (median 

precipitation less than 28 inches) were 1963, 1966, 1976, 

1988, and 1989. The 5 wettest years (median precipitation 

more than 40 inches) were 1965, 1973, 1990, 1993, and 1998. 

The effects of conservation practices estimated in this study 

reflect these extreme conditions. 

Because farming activities represent the time period 2003 to 

2006, model results do not indicate environmental outcomes 

for each year of the 47 years. 

 

15 The 47-year record is the extent of a serially complete daily data set of 

weather station data from weather station records available from the NCDC 

(National Climatic Data Center), for the period 1960 to 2006, including 

precipitation, temperature maximum, and temperature minimum (Eischeid et 

al., 2000). 
Draft June 2010 Page 24 

Figure 8. Annual precipitation used in the model simulations, by year, for the Upper Mississippi River Basin 

Note: This figure shows how annual precipitation varied within the region and from year to year in the model simulation. Each of the 47 curves shown above represents 

a single year of data and shows how annual precipitation varied over the region in that year, starting with the driest acres within the region and increasing to the wettest 

acres for each year. The family of curves shows how annual precipitation varied from year to year. Annual precipitation over the 47-year simulation averaged about 34 

inches. The top curve shown is for the year 1993, the wettest year on record in this region. The curve for 1993 shows that precipitation exceeded 40 inches per year for 

about 75 percent of cropped acres in the UMRB. 

Rather, model results represent what would be expected to occur 

under varying weather conditions for farming activities 

conducted in the period 2003–06. For most analyses, model 

results are averaged over the 47 years and reported as average 

annual values. These average annual estimates thus represent 

environmental outcomes that would be expected over the long 

run. 

Simulating the no-practice scenario 

The purpose of the no-practice scenario is to provide an estimate 

of the benefits of conservation practices in use within the 

UMRB. The only difference between the no-practice scenario 

and the baseline conservation condition is that the conservation 

practices are removed or their effects are reversed in the nopractice scenario simulations. There were usually several 

alternatives that could be used to represent “no practices.” The 

no-practice representations derived for use in this study 

conformed to the following guidelines. 

 Consistency: It is impossible to determine what an 

individual farmer would be doing if he or she had not 

adopted certain practices, so it is important to represent all 

practices on all sample points in a consistent manner that is 

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. 

Complexity would not only complicate the modeling 

process but also hamper the interpretation of results. 

 Historical context avoided: The no-practice scenario is a 

technological step backward for conservation, not a 

chronological step back to a prior era when conservation 

practices were not used. Although the advent of certain 

conservation technologies can be dated, the adoption of 

technology is gradual, regionally diverse, and ongoing. It is 

also important to retain the overall crop mix in the region, as 

it in part reflects today’s market forces. Therefore, moving 

the clock back to 1950s (or any other time period) 

10

15

20

25

30

35

40

45

50

55

60

0 10 20 30 40 50 60 70 80 90 100

Annual precipitation (inches/year)

Cumulative percent acres
Draft June 2010 Page 25 

agriculture is not the goal of the no-practice scenario. 

Taking away the conservation ethic is the goal. 

 Moderation: The no-practice scenario should provide a 

reasonable level of “poor” conservation so that a believable 

benefit can be determined, where warranted, but not so 

severe as to generate exaggerated conservation gains by 

simulating the worst-case condition. Tremendous benefits 

could be generated if, for example, nutrients were applied at 

twice the recommended rates with poor timing or 

application methods in the no-practice simulation. Similarly, 

large erosion benefits could be calculated if the no-practice 

representation for tillage was fall plowing with moldboard 

plows and heavy disking, which was once common but 

today would generally be considered economically 

inefficient. 

 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. The 

same guideline was followed for pest control—the suite of 

pesticides used was not adjusted in the no-practice scenario 

because of the likelihood that alternative pesticides would 

not be as effective and would result in lower yields under 

actual conditions. 

A deliberate effort was made to adhere to these guidelines to the 

same degree for all conservation practices so that the overall 

level of representation would be equally moderate for all 

practices. Table 6 summarizes the adjustments to conservation 

practices used in simulation of the no-practice scenario. 

Table 6. Construction of the no-practice scenario 

Practice adjusted Level of criteria 

Criteria used to determine if a practice 

was in use 

Adjustment made to create the no-practice scenario 

Residue management (tillage) Crop within a crop year STIR ≤100 Add two tandem diskings 1 week prior to planting 

Nitrogen rate – without manure Crop within a crop year Applied N ≤1.4 times harvest removal 

for non-legume crops 

Increase rate to 1.64 times harvest removal 

(proportionate increase in all reported applications) 

Phosphorus rate – without 

manure 

Crop rotation Applied P ≤1.1 times harvest removal for 

all crops in rotation 

Increase rate to 1.6 times harvest removal 

(proportionate increase in all reported applications) 

Nitrogen rate – with manure Crop within a crop year Applied total of fertilizer and manure N 

≤1.4 times harvest removal for all crops 

Increase manure and N fertilizer application rates to 

reach 1.64 times harvest removal (all applications 

increased proportionately) 

Phosphorus rate – with manure Crop rotation Applied total of fertilizer and manure P ≤

1.1 times harvest removal, accounting also 

for manure P associated with increase to 

meet N criteria 

Increase P fertilizer application rates to reach1.6 times 

harvest removal, accounting for increased manure due 

to the N criteria 

Fertilizer application method Application event Incorporated or banded Change to surface broadcast 

Manure application method Application event Incorporated, banded, or injected Change to surface broadcast 

Fertilizer application timing Application event Within 3 weeks prior to planting, at 

planting, or within 60 days after planting. 

Moved to 3 weeks prior to planting 

Cover crop Crop year Cover crop planted for off-season 

protection 

Remove cover crop simulation (field operations, 

fertilizer, grazing, etc.) 

Pesticide Sample 1. Practicing high level of IPM 

2. Practicing moderate level of IPM 

1. All incorporated applications changed to surface 

application. For each crop, the first application 

event after planting and 30 days prior to harvest 

replicated twice, 1 week and 2 weeks later than 

original. 

2. Same as for high level of IPM, except replication 

of first application only 1 time, 1 week after 

original 

Irrigation Crop year Pressure systems Change to Hand Move Sprinkler Systems 

Structural practices Sample 1. Overland flow practices present 

2. Concentrated flow—managed 

structures or waterways present 

3. Edge-of-field mitigation practices 

present 

4. Wind erosion control practices 

present 

1. USLE P-factor changed to 1 and slope length 

increased for points with terraces, soil condition 

changed from good to poor. 

2. Structures and waterways replaced with earthen 

ditch, soil condition changed from good to poor. 

3. Removed practice and width added back to field 

slope length. 

4. Unsheltered distance increased to 400 meters 
Draft June 2010 Page 26 

No-practice representation of conservation tillage. The nopractice tillage protocols are designed to remove the benefits 

of conservation tillage. For all crops grown with some kind of 

reduced tillage, including cover crops, the no-practice scenario 

simulates conventional tillage, based on the STIR (Soil 

Tillage Intensity Rating) value. Conventional tillage for the 

purpose of estimating conservation benefits is defined as any 

crop grown with a STIR value above 100. (To put this in 

context, no-till or direct seed systems have a STIR of less than 

30, and that value is part of the technical standard for Residue 

Management, No-Till/Strip Till/Direct Seed [NRCS Practice 

Standard 329]). Those crops grown with a STIR value of less 

than 100 in the baseline conservation condition had tillage 

operations added in the no-practice scenario. 

Simulating conventional tillage for crops with a STIR value of 

less than 100 requires the introduction of additional tillage 

operations in the field operations schedule. For the no-practice 

scenario, two consecutive tandem disk operations were added 

prior to planting. In addition to adding tillage, the hydrologic 

condition for assignment of the runoff curve number was 

changed from good to poor on all points receiving additional 

tillage. Points that are conventionally tilled for all crops in the 

baseline condition scenario are also modeled with a “poor“ 

hydrologic condition curve number. 

The most common type of tillage operation in the survey was 

disking, and the most common disk used was a tandem disk 

for nearly all crops, in all parts of the region, and for both 

dryland and irrigated agriculture. The tandem disk has a STIR 

value of 39 for a single use. Two consecutive disking 

operations will 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. Although a few 

sample points will have STIR values in the 80s or 90s after 

adding the two disking operations, the consistency of an 

across-the-board increase of 78 is simple and provides the 

effect of a distinctly more intense tillage system. 

These additional two tillage operations were inserted in the 

simulation one week prior to planting, one of the least 

vulnerable times for tillage operations because it is close to the 

time when vegetation will begin to provide cover and 

protection. 

No-practice representation of structural practices. The nopractice field condition for structural practices is simply the 

removal of the structural practices from the modeling process. 

In addition, the soil condition is changed from “Good” to 

“Poor” for the determination of the runoff curve number for 

erosion prediction. 

 Overland flow: This group includes such practices as 

terraces and contouring which slow the flow of water 

across the field. For the practices affecting overland flow 

of water and therefore the P factor of the USLE-based 

equations, the P factor was increased to 1. Slope length is 

also changed for practices such as terraces to reflect the 

absence of these slope-interrupting practices. 

 Concentrated flow: This group of practices is designed 

to address channelized flow and includes grassed 

waterways and grade stabilization structures. These 

practices are designed to prevent areas of concentrated 

flow from developing gullies or to stabilize gullies that 

have developed. The no-practice protocol for these 

practices removes the structure or waterway and replaces 

it with a “ditch” as a separate subarea. This ditch, or 

channel, represents a gully; however, the only sediment 

contributions from the gully will come from downcutting. 

Headcutting and sloughing of the sides are not simulated 

in APEX. 

 Edge of field: These practices include buffers, filters, and 

other practices that occur outside the primary production 

area and act to mitigate the losses from the field. The nopractice protocol removes these areas and their 

management. The width of these practices will be 

returned to the slope lengths as well. (When simulating a 

buffer in APEX, the slope length reported in the NRI is 

adjusted.) 

 Wind control: Practices such as windbreaks or 

shelterbelts, cross wind ridges, stripcropping or trap 

strips, and hedgerows are examples of practices used for 

wind control. The unsheltered distance reflects the 

dimensions of the field as modeled, 400 meters or 1,312 

feet. Any practices reducing the unsheltered distance are 

removed and the unsheltered distance set to 400 meters. 

No-practice representation of cover crops. The no-practice 

protocol for this practice removes the planting of the crop and 

all associated management practices such as tillage and 

fertilization. In a few cases the cover crops were grazed; when 

the cover crops are removed so are the grazing operations. 

No-practice representation of nutrient management 

practices. The no-practice nutrient management protocols are 

designed to remove the benefits of proper nutrient 

management techniques. The NRCS Nutrient Management 

standard (590) allows a variety of methods to reduce nutrient 

losses while supplying a sufficient amount of nutrient to meet 

realistic yield goals. The standard addresses nutrient loss in 

one of two primary ways: (1) by altering rates, form, timing, 

and methods of application, or (2) by installing buffers, filters, 

or erosion or runoff control practices to reduce mechanisms of 

loss. The latter method is covered by the structural practices 

protocols for the no-practice scenario. The goals of the 

nutrient management protocols are to alter 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. 

 Nitrogen rate: For the no-practice scenario, the amount 

of commercial nitrogen fertilizer applied was increased to 

1.64 times harvest removal for non-legume crops 

receiving less than or equal to 1.40 times the amount of 

nitrogen removed at harvest. The ratio of 1.64 for the 

increased nitrogen rate was determined by the average 

rate-to-yield-removal ratio for crops exceeding 1.4. 
Draft June 2010 Page 27 

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, both 

manure and fertilizer, and both fertilizer and manure were 

increased proportionately to reach the 1.64 times harvest 

removal threshold. The assessment for using appropriate 

nitrogen application rates was made on an average annual 

basis for each crop in the rotation using average annual 

model output for nitrogen removed at harvest in the 

baseline conservation condition scenario. 

 Phosphorus rate: The no-practice scenario for 

phosphorus is similar to that for nitrogen, but with a lower 

threshold. The lower threshold was used because 

phosphorus is not lost through volatilization to the 

atmosphere and much less is lost through other pathways 

owing to strong bonding of phosphorus to soil particles. 

The threshold for identifying proper phosphorus 

application rates was 1.1 times the amount of phosphorus 

taken up by the crop and removed at harvest. For the nopractice scenario, the amount of phosphorus applied was 

increased to 1.6 times the harvest removal rate. For crops 

receiving manure, the increase in P from manure added to 

meet the N criteria was taken into account. The ratio of 

1.6 for the increased phosphorus rate was determined by 

the average rate-to-yield-removal ratio for crops 

exceeding 1.1. Fertilizer application events were 

increased proportionately to meet the 1.6 threshold. No 

adjustment was made to manure to meet the P threshold. 

No adjustment was made in the no-practice scenario for 

manure applications exceeding a phosphorus basis for the 

manure application rate. 

 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 no-practice 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. 

 Method of application: Nutrient applications, including 

manure applications, that were incorporated or banded 

were changed to a surface broadcast application method. 

No-practice representation of irrigation practices. The nopractice irrigation protocols focus on reducing efficiencies 

both of water delivery from the source to the field and of 

application methods. 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. All conservation practices, 

such as irrigation water management, were removed and 

samples with pressurized systems were changed to “hand 

move sprinklers.” All but three of the 66 cases of irrigated 

crops used a Center Pivot system in the baseline conservation 

condition. The other three included two with Big Gun and 

one Open Discharge Flood system. The Open Discharge Flood 

system was unchanged. 

No-practice representation of pesticide management 

practices. Pesticide management for conservation purposes is 

a combination of three types of interrelated management 

activities: 

1. A mix of conservation practices that retain pesticide 

residues within the farm field boundaries. 

2. Pesticides and pesticide application practices that 

minimize the risk that pesticide residue poses to the 

surrounding environment. 

3. Practice of Integrated Pest Management (IPM) at a high 

level. 

The first activity is covered by the no-practice representation 

of structural practices and residue and tillage management. 

The second activity, for the most part, cannot be simulated in 

large-scale regional modeling because of the difficulty in 

assuring that any changes in the types of pesticides applied or 

in the method or timing of application would provide 

sufficient protection against pests to maintain crop yields.16

Farmers, of course, have such options, and environmentally 

conscientious farmers make tradeoffs to reduce environmental 

risk. But without better information on the nature of the pest 

problem both at the field level and in the surrounding area, 

modelers have to resort to prescriptive and generalized 

approaches to simulate alternative pesticides and application 

techniques, which would inevitably be inappropriate for many, 

if not most, of the acres simulated. 

The no-practice representation for pesticide management is 

therefore based on the third type of activity—practicing IPM. 

An IPM indicator was developed on the basis of survey 

responses to IPM-related questions in the NRI-CEAP 

Cropland Survey. 

Adoption of IPM systems normally occurs along a continuum 

from largely reliant on prophylactic control measures and 

pesticides to multiple-strategy, biologically intensive 

approaches, and is not usually an either/or situation. The 

practice of IPM is site-specific in nature, with individual 

tactics determined by the particular crop/pest/environment 

scenario. Where appropriate, each site should have in place a 

management strategy for Prevention, Avoidance, 

Monitoring, and Suppression of pest populations (the PAMS

approach) (Coble, 1998). In order to qualify as IPM 

practitioners, growers should use tactics in all four PAMS 

components. 

Prevention is the practice of keeping a pest population from 

infesting a field or site, and should be the first line of defense. 

 

16 The APEX model can simulate pesticide applications, but it does not 

currently include a pest population model that would allow simulation of the 

effectiveness of pest management practices. Thus, the relative effectiveness of 

pesticide substitution or changes in other pest management practices cannot be 

evaluated. 
Draft June 2010 Page 28 

It includes such tactics as using pest-free seeds and 

transplants, preventing weeds from reproducing, irrigation 

scheduling to avoid situations conducive to disease 

development, cleaning tillage and harvesting equipment 

between fields or operations, using field sanitation procedures, 

and eliminating alternate hosts or sites for insect pests and 

disease organisms. 

Avoidance may be practiced when pest populations exist in a 

field or site but the impact of the pest on the crop can be 

avoided through some cultural practice. Examples of 

avoidance tactics include crop rotation in which the crop of 

choice is not a host for the pest, choosing cultivars with 

genetic resistance to pests, using trap crops or pheromone 

traps, choosing cultivars with maturity dates that may allow 

harvest before pest populations develop, fertilization programs 

to promote rapid crop development, and simply not planting 

certain areas of fields where pest populations are likely to 

cause crop failure. 

Monitoring and proper identification of pests through surveys 

or scouting programs, including trapping, weather monitoring 

and soil testing where appropriate, should be performed as the 

basis for suppression activities. Records should be kept of pest 

incidence and distribution for each field or site. Such records 

form the basis for crop rotation selection, economic 

thresholds, and suppressive actions. 

Suppression of pest populations may become necessary to 

avoid economic loss if prevention and avoidance tactics are 

not successful. Suppressive tactics include cultural practices 

such as narrow row spacing or optimized in-row plant 

populations, alternative tillage approaches such as no-till or 

strip-till systems, cover crops or mulches, or using crops with 

allelopathic potential in the rotation. Physical suppression 

tactics include cultivation or mowing for weed control, baited 

or pheromone traps for certain insects, and temperature 

management or exclusion devices for insect and disease 

management. Biological controls, including mating disruption 

for insects, should be considered as alternatives to 

conventional pesticides, especially where long-term control of 

an especially troublesome pest species can be obtained. Where 

naturally occurring biological controls exist, effort should be 

made to conserve these valuable tools. Chemical pesticides are 

important in IPM programs, and some use will remain 

necessary. However, pesticides should be applied as a last 

resort in suppression systems using a sound management 

approach. 

An IPM index was developed to determine the level of IPM 

activity for each sample point. The index was constructed as 

follows: 

 Scores were assigned to each question by a group of IPM 

experts. 

 Scores for each PAMS category were normalized to have 

a maximum score of 100. 

 The four PAMS categories were also scored in terms of 

relative importance for an IPM index: prevention = 1/6, 

avoidance = 1/6, monitoring = 1/3, and suppression = 1/3. 

 The IPM indicator was calculated by multiplying the 

normalized PAMS category by the category weight and 

summing over the categories. 

For samples classified as having either high or moderate IPM 

use, all soil-incorporated pesticide applications in the baseline 

condition were changed to surface applications. For high IPM 

cases, the first application event between planting and 30 days 

before harvest was replicated twice for each crop, one week 

and two weeks after its original occurrence. For moderate 

IPM cases, the first application event was replicated one time 

for each crop, one week after its original occurrence. 

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. For each CRP sample point, a set of cropping 

simulations was developed to represent the probable mix of 

management that would be applied to the point if it were 

cropped. 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 to create a new simulation. 
Draft June 2010 Page 29 

Chapter 3 

The Baseline Conservation Condition 

Overview and Summary of Findings 

The use of conservation practices in the UMRB closely 

reflects the history of Federal conservation programs and 

technical assistance. In the beginning the focus was almost 

entirely on reducing soil erosion and the preserving the soil’s 

productive capacity. In the 1930s and 1940s, Hugh Hammond 

Bennett, the founder and first chief of the Soil Conservation 

Service (now Natural Resources Conservation Service) 

instilled in the national ethic the need to treat every acre to its 

potential by controlling soil erosion and water runoff. Land 

shaping structural practices (such as terraces, contour farming, 

and strip cropping) and sediment control structures were 

widely adopted. Conservation tillage emerged in the 1960s 

and 1970s as a key management practice for enhancing soil 

quality and further reducing soil erosion. Conservation tillage, 

along with use of crop rotations and cover crops, was used 

either alone or in combination with structural practices to 

further reduce soil erosion on cropland. The conservation 

compliance provisions in the 1985 Farm Bill sharpened the 

focus to treatment of the most erodible acres, tying farm 

commodity payments to conservation treatment of highly 

erodible land. The Conservation Reserve Program was 

established to enroll the most erodible cropland acres in multiyear contracts to plant acres in long-term conserving cover. 

During the late 1990s, the focus of conservation efforts began 

to shift from soil conservation and sustainability to reducing 

pollution impacts associated with agricultural production. 

Prominent among new concerns were the environmental 

effects of nutrient export from farm fields. Traditional 

conservation practices used to control surface water runoff and 

erosion control were mitigating a significant portion of these 

nutrient losses, but additional gains were being achieved using 

nutrient management practices—application of nutrients 

(appropriate timing, rate, method, and form) to minimize 

losses to the environment and maximize the availability of 

nutrients for crop growth. 

This study assessed the use and effectiveness of conservation 

practices in the UMRB for the period 2003 to 2006 to 

determine the baseline conservation condition for the region. 

The baseline conservation condition provides a benchmark for 

estimating the effects of existing conservation practices as 

well as projecting the likely effects of alternative conservation 

treatments. Conservation practices that were evaluated include 

structural practices, annual practices, and long-term 

conserving cover. 

Structural conservation practices, once implemented, are 

usually kept in place for several years. Designed primarily for 

erosion control, they also mitigate edge-of-field nutrient and 

pesticide loss. Structural practices evaluated include— 

 in-field practices for water erosion control, divided into 

two groups: 

o practices that control overland flow (terraces, contour 

buffer strips, contour farming, stripcropping, contour 

stripcropping), and 

o 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, field borders); and 

 wind erosion control practices (windbreaks/shelterbelts, 

cross wind trap strips, herbaceous wind barriers, 

hedgerow planting). 

Annual conservation practices are management practices that 

are conducted as part of the crop production system each year. 

These practices are designed primarily to promote soil quality, 

reduce in-field erosion, and reduce the availability of 

sediment, nutrients, and pesticides for transport by wind or 

water. They include— 

 residue and tillage management; 

 nutrient management practices; 

 pesticide management practices; and 

 cover crops. 

Long-term conservation cover establishment consists of 

planting suitable native or domestic grasses, forbs, or trees on 

environmentally sensitive cultivated cropland. 

The effects of conservation crop rotation practices (NRCS 

practice code 328) were not assessed. This practice consists of 

growing different crops in a planned rotation to manage 

nutrient inputs, enhance soil quality, or reduce soil erosion. In 

the UMRB, crop rotations that meet NRCS criteria occur on 

over 90 percent of the cropped acres, often for reasons 

unrelated to conservation benefits, such as the control of pests 

or in response to changing markets. In contrast, only 25 

percent of survey respondents had conservation crop rotation 

included in a written conservation plan. Estimating the effects 

of conservation crop rotation practices requires simulation of 

continuous cropping systems for all crops, for which adequate 

information on chemical use and other farming practices was 

not available. 

Given the long history of conservation in the UMRB, it is not 

surprising to find that nearly all cropped acres in the region 

have evidence of some kind of conservation practice, 

especially erosion control practices. The conservation practice 

information collected during the study was used to assess the 

extent of conservation practice use. Key findings are: 

 Structural practices for controlling water erosion are in 

use on 45 percent of cropped acres (table 7). On the 18 

percent of the acres designated as highly erodible land, 

structural practices designed to control water erosion are 

in use on 72 percent of those acres. 

 Tillage and residue management use is common (table 8). 

o About 71 percent of the acres meet tillage intensity 

criteria for either no-till or mulch till and are gaining 

soil organic carbon, including 62 percent of the 

highly erodible land. 
Draft June 2010 Page 30 

o Overall, 75 percent of the acres are gaining soil 

organic carbon. 

o All but 5 percent of the acres had evidence of some 

kind of reduced tillage on at least one crop. 

 Producers use either residue and tillage management 

practices or structural practices, or both, on 96 percent of 

the acres, including 98 percent of the highly erodible land. 

 While most acres have evidence of some nitrogen or 

phosphorus management, the majority of the acres in the 

region lack consistent use of appropriate rates, timing, 

and method of application on each crop in every year of 

production, including most of the acres receiving manure 

(table 9). 

o Appropriate rates of nitrogen application are in use 

on about 34 percent of the acres for all crops in the 

rotation. 

o Appropriate nitrogen application rates, timing of 

application, and application method for all crops 

during every year of production, however, are in use 

on only about 14 percent of the acres, including acres 

without nitrogen applications. 

o About 86 percent of the acres lack consistent use of 

appropriate nitrogen application rates and/or time of 

nitrogen application, including nearly all of the acres 

receiving manure. 

o Good phosphorus management practices (appropriate 

rate, timing, and method) are in use on 29 percent of 

the acres on all crops during every year of 

production, including acres without phosphorus 

applications. 

o About 71 percent of the acres lack consistent use of 

appropriate phosphorus application rates and/or 

method of phosphorus application, including nearly 

all of the acres receiving manure. 

 The Integrated Pest Management (IPM) indicator showed 

that only about 10 percent of the acres were being 

managed with a relatively high level of IPM. 

 Land in long-term conserving cover, as represented by 

enrollment in the CRP General Signup, consists of 2.8 

million acres in the region, of which 67 percent are highly 

erodible land. 

Structural Conservation Practices 

Data on structural practices for the farm field associated with 

each sample point were obtained from four sources: 

1. The NRI-CEAP Cropland Survey included questions 

about the presence of 12 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, 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 that were enrolled in the 

Continuous CRP for these structural practices: contour 

grass strips, filter strips, grassed waterways, riparian 

buffers (trees), and field windbreaks (Alex Barbarika, 

USDA/FSA, personal communication). 

4. The 2003 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, cross wind stripcropping, cross wind trap strips, 

diversions, field borders, filter strips, grassed waterways 

or outlets, hedgerow planting, herbaceous wind barriers, 

riparian forest buffers, and windbreak or shelterbelt 

establishment. 

Overland flow control practices are designed to slow the 

movement of water across the soil surface to reduce 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. These practices are found on about 21 percent of the 

cropped acres in the UMRB, including 46 percent of those that 

are classified as highly erodible land (table 7). 

Concentrated flow control practices are designed to prevent 

the development of gullies along flow paths within the field. 

NRCS practice standards for concentrated flow control 

practices include grassed waterways, grade stabilization 

structures, diversions, and water and sediment control basins. 

This is the most prevalent group of structural practices in the 

UMRB; about 32 percent of the cropped acres have one or 

more of these practices, including 55 percent of the highly 

erodible land. 

Edge-of-field buffering and filtering practices, consisting of 

grasses, shrubs, and/or trees, are designed to capture the 

surface runoff losses that were not avoided or mitigated by the 

in-field practices. NRCS practice standards for edge-of-field 

mitigation practices include edge-of-field filter strips, riparian 

herbaceous buffers, and riparian forest buffers. CRP’s buffer 

practices are included in this category. Edge-of-field buffering 

and filtering practices are in use on about 9 percent of all 

cropped acres in the region. 

Wind erosion control practices are designed to reduce the 

force of the wind on the field. NRCS practice standards for 

wind erosion control practices include cross wind ridges, cross 

wind trap strips, herbaceous wind barriers, and 

windbreak/shelterbelt establishment. Wind erosion is not a 

resource concern for most acres in this region. Only about 3 

percent of the cropped acres in the region are treated for wind 

erosion using structural practices. 

 
Draft June 2010 Page 31 

Table 7. Structural conservation practices in use for the baseline conservation condition, Upper Mississippi River Basin 

Structural practice 

category Conservation practice in use 

Percent 

of nonHEL Percent of 

HEL 

Percent of 

all acres 

Overland flow control 

practices Terraces, contour buffer strips, contour farming, stripcropping, 

contour stripcropping, field border, in-field vegetative barriers 15 46 21 

Concentrated flow 

control practices Grassed waterways, grade stabilization structures, diversions, 

other structures for water control 27 55 32 

Edge-of-field buffering 

and filtering practices Riparian forest buffers, riparian herbaceous buffers, filter strips 10 8 9 

One or more water 

erosion control practices Overland flow, concentrated flow, or edge-of-field practice 39 72 45 

Wind erosion control 

practices 

Windbreaks/shelterbelts, crosswind trap strips, herbaceous 

windbreak, hedgerow planting 3 3 3 

Note: About 18.4 percent of cropped acres in the UMRB are highly erodible land (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. 
Draft June 2010 Page 32 

Overall, about 45 percent of the cropped acres in the UMRB 

are treated with one or more water erosion control structural 

practices (table 7). The treated percentage for highly erodible 

land acres is much higher—72 percent. 

The structural conservation practices for water erosion control 

in use for each sample were classified as either a high level of 

treatment, moderately high level of treatment, moderate level 

of treatment, or low level of treatment. Criteria for each 

treatment level are presented in figure 9. These treatment 

levels are combined with soil risk classes to estimate acres that 

appear to be under-treated for water erosion control in chapter 

6. 

As shown in figure 9, only about 5 percent of cropped acres in 

the region have a high level of treatment (combination of 

edge-of-field buffering or filtering and at least one in-field 

structural practice). About 55 percent of the acres do not have 

structural practices for water erosion control; however, some 

of the fields with slopes less than 2 percent do not need to be 

treated with structural practices. 

Figure 9. Conservation treatment levels for structural practices, baseline conservation condition, UMRB

Criteria for four levels of treatment with structural conservation practices are: 

 High treatment: Edge-of-field mitigation and at least one in-field structural practice (concentrated flow or overland flow 

practice) required. 

 Moderately high treatment: Either edge-of-field mitigation required or both concentrated flow and overland flow practices 

required. 

 Moderate treatment: No edge-of-field mitigation, either concentrated flow or overland flow practices required. 

 Low treatment: No edge-of-field or in-field structural practices. 

Low Moderate Moderately 

high High

Slope 2 percent or less 36.6 12.5 6.1 2.4

Slope greater than 2 percent 18.0 13.2 8.7 2.4

0

10

20

30

40

50

60

Percent of cropped acres
Draft June 2010 Page 33 

Residue and Tillage Management Practices 

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 applied. 

The Soil Tillage Intensity Rating (STIR) (USDA-NRCS 

2007)17 was used to determine the soil disturbance intensity 

for each crop at each sample point. The soil disturbance 

intensity is a function of the kinds of tillage, the frequency of 

tillage, and the depth of tillage. STIR values were calculated 

for each crop and for each of the 3 years covered by the NRICEAP Cropland Survey (accounting for multiple crops or 

cover crops). By combining the STIR values for each crop 

year with model output on the long-term trend in soil organic 

carbon gain or loss, eight categories of residue and tillage 

management were identified, as defined in table 8. 

Overall, 91 percent of cropped acres in the UMRB meet the 

tillage intensity rating for no-till or mulch till (table 8). About 

28 percent meet the criteria for no-till--23 percent with gains 

in soil organic carbon and 5 percent with soil organic carbon 

loss. Most cropped acres (63 percent) meet the tillage intensity 

criteria for mulch till--48 percent with gains in soil organic 

carbon and 15 percent with soil organic carbon loss. No-till is 

used more frequently on highly erodible land than on nonhighly erodible land. Only 5 percent of the acres are 

conventionally tilled for all crops in the rotation. 

Four levels of treatment for residue and tillage management 

practices were derived according to criteria presented in figure 

10. These treatment levels are combined with soil risk classes 

to estimate acres that appear to be under-treated for water 

erosion control in chapter 6. The high and moderately high 

treatment levels represent the 71 percent of the acres that meet 

tillage intensity criteria for either no-till or mulch till with 

gains in soil organic carbon. The high treatment level (63 

percent of the acres) includes only those acres where the 

tillage intensity criteria are met for each crop in the rotation. 

Only 3 percent of the acres have a low treatment level, 

consisting of continuous conventional tillage for all crops in 

the rotation and loss of soil organic carbon. 

Cover Crops 

Cover crops are planted when the principal crops are not 

growing. The two most important functions of cover crops are 

(1) to provide soil surface cover and reduce soil erosion, and 

(2) to utilize and convert excess nutrients remaining in the soil 

from the preceding crop into plant biomass, thereby reducing 

nutrient leaching and minimizing the amount of soluble 

nutrients in runoff during the non-crop growing season. Cover 

crops also contribute to soil quality by capturing atmospheric 

carbon in plant tissue and adding it to the soil carbon. 

 

17 A description of the Soil Tillage Intensity Rating (STIR) can be found at 

http://stir.nrcs.usda.gov/. 

The presence or absence of cover crops was determined from 

farmer responses in the NRI-CEAP Cropland Survey. The 

following criteria were used to identify a cover crop: 

 A cover crop must be a close-grown crop that is not 

harvested as a principal crop, or if it is harvested, must 

have been specifically identified in the NRI-CEAP 

Cropland Survey as a cover crop as an indicator that the 

harvest was for an acceptable purpose (such as biomass 

removal or use as mulch or forage material). 18 

 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 sugar beets and potatoes. 

Early spring vegetation protects young crop seedlings. 

In the UMRB, cover crops are rarely used as a conservation 

practice. Less than 1 percent of the acres (13 sample points) 

meet the criteria for a cover crop. Climate is likely to play a 

large role in its lack of adoption, since the growing season in 

much of the basin is too short to establish a cover crop 

following fall-harvested crops. Farmers in the portions of the 

basin where the climate is warmer and the growing season is 

longer are more likely to double crop with winter wheat rather 

than to plant a small grain winter cover crop.

Irrigation Management Practices 

Only about 2.5 percent of the cropland—1.5 million acres—

receives irrigation water in the UMRB. Irrigation in the region 

is almost exclusively by pressure systems. Most common are 

center-pivot or linear-move systems with impact sprinkler 

heads (56 percent) followed by center-pivot or linear-move 

with the more efficient low-pressure spray (34 percent). Big 

gun sprinklers make up 4 percent of the systems, and the most 

efficient system, center pivot or linear-move with near-ground 

emitters, are another 3 percent. Because of the small number 

of irrigation systems reported for the region, the conservation 

effects of irrigation management practices were not evaluated. 

 

18 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. 
Draft June 2010 Page 34 

Table 8. Residue and tillage management practices for the baseline conservation condition, Upper Mississippi River Basin 

Residue and tillage management practice in use 

Percent of 

non-HEL 

Percent of 

HEL 

Percent of 

all acres 

Acres with carbon gain 78 63 75 

Average annual tillage intensity for crop rotation meets criteria for no-till* 20 36 23 

Average annual tillage intensity for crop rotation meets criteria for mulch till** 53 26 48 

Reduced tillage on some crops in rotation but average annual tillage intensity greater than criteria 

for mulch till 3 1 2 

Continuous conventional tillage in every year of crop rotation*** 2 1 2 

Acres with carbon loss 22 37 25 

Average annual tillage intensity for crop rotation meets criteria for no-till* 2 14 5 

Average annual tillage intensity for crop rotation meets criteria for mulch till** 14 20 15 

Reduced tillage on some crops in rotation but average annual tillage intensity greater than criteria 

for mulch till 2 2 2 

Continuous conventional tillage in every year of crop rotation*** 4 2 3 

* Average annual Soil Tillage Intensity Rating (STIR) over all crop years in the rotation is less than 30. 

** Average annual Soil Tillage Intensity Rating (STIR) over all crop years in the rotation is between 30 and 100. 

*** Soil Tillage Intensity Rating (STIR) for every crop year in the rotation is more than 100. 

HEL = highly erodible land. 

Note: Percents may not add to totals because of rounding. 

Figure 10. Conservation treatment levels for residue and tillage management, baseline conservation condition, UMRB 

Criteria for four levels of treatment with residue and tillage management are: 

 High treatment: All crops meet tillage intensity criteria for either no-till or mulch till and crop rotation is gaining soil organic 

carbon. 

 Moderately high treatment: Average annual tillage intensity meets criteria for mulch till or no-till and crop rotation is gaining 

soil organic carbon; some crops in rotation exceed tillage intensity criteria for mulch till. 

 Moderate treatment: Some crops have reduced tillage but do not meet criteria for high or moderately high treatment or crop 

rotation is gaining soil organic carbon; most acres in this treatment level are losing soil organic carbon. 

 Low treatment: Continuous conventional tillage and crop rotation is losing soil organic carbon. 

Low Moderate Moderately 

high High

Losing carbon 3.4 21.2 0.0 0.0

Gaining carbon 0.0 4.2 8.7 62.6

0

10

20

30

40

50

60

70

Percent of cropped acres
Draft June 2010 Page 35 

Nutrient Management Practices 

Nitrogen and phosphorus are essential inputs to profitable crop 

production. Farmers apply these nutrients to the land as 

commercial fertilizers and manure to promote plant growth 

and increase crop yields. Not all of the nutrients applied to the 

land, however, are taken up by crops; some are lost to the 

environment and, when combined with naturally occurring 

levels of these elements, can create human health risks and 

other offsite environmental problems. 

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.) 

Such systems are tailored to address the specific cropping 

system, nutrient sources available, and site characteristics of 

each field. All nutrient management systems have four basic 

criteria for application of commercial fertilizers and manure. 

1. Apply nutrients at the appropriate rate based on soil and 

plant tissue analyses and realistic yield goals. 

2. Apply the appropriate form of fertilizer and organic 

material with compositions and characteristics that resist 

nutrient losses from the agricultural management zone. 

3. Apply at the appropriate time to supply nutrients to the 

crop when the plants have the most active uptake and 

biomass production, and avoid times when adverse 

weather conditions can result in large losses of nutrients 

from the agricultural management zone. 

4. Apply using the appropriate application method that 

provides nutrients to the plants for rapid, efficient uptake 

and reduces the exposure of nutrient material to forces of 

wind and water. 

Depending on the field characteristics, these 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 by careful management and 

kept within an acceptable level. 

The presence or absence of nutrient management practices 

was based on information on the timing, rate, and method of 

application for manure and commercial fertilizer as reported 

by the producer in the NRI-CEAP Cropland Survey. The 

appropriate form of nutrients applied was not evaluated 

because the survey was not sufficiently specific about the 

material formulations that were applied. The following criteria 

were used to identify the appropriate rate, time, and method of 

nutrient application on a crop-by-crop basis: 

 All commercial fertilizer and manure applications are 

within 3 weeks prior to plant date, at planting, or within 

60 days after planting. 

 The method of application for commercial fertilizer or 

manure is some form of incorporation or banding. 

 Where only commercial fertilizer is applied— 

o the rate of commercial nitrogen fertilizer application 

is less than 1.4 times the amount of nitrogen removed 

in the crop yield at harvest; or 

o the rate of commercial phosphorus fertilizer 

application is less than 1.1 times the amount of 

phosphorus removed in the crop yield at harvest. 

 Where manure is applied, the sum of the nitrogen in 

commercial fertilizer and the nitrogen in the manure is 

less than 1.4 times the amount of nitrogen removed in the 

crop yield at harvest. A nitrogen basis for manure 

applications is considered sufficient to meet requirements 

for nutrient management.19

These nutrient management criteria are intended to represent 

practice recommendations commonly found in nutrient 

management conservation plans. Some conservation plans 

have requirements that are less stringent, while others include 

more stringent nutrient management practices. The criteria 

used here to identify the occurrence of nutrient management 

practices, while generally consistent with NRCS standards, do 

not necessarily represent the best possible or even the best 

practical set of nutrient management practices. 

As shown in table 9, most acres with nutrients applied meet 

one or more of the criteria for nutrient management in the 

UMRB: 

 45 percent of acres meet criteria for timing of nitrogen 

applications, mostly acres not receiving manure. 

 56 percent of acres meet criteria for method of nitrogen 

application. 

 34 percent of acres meet criteria for nitrogen application 

rate. 

 50 percent of acres meet criteria for timing of phosphorus 

applications, mostly acres not receiving manure. 

 57 percent of acres meet criteria for method of 

phosphorus application. 

 57 percent of acres meet criteria for phosphorus 

application rate. 

However, few acres meet all criteria. Overall, only 14 percent 

of the acres meet all criteria for nitrogen applications. Another 

2 percent of cropped acres did not apply nitrogen. Proper 

phosphorus management is more common; 29 percent of the 

acres meet all criteria for phosphorus applications. About 1 

percent of the acres did not apply phosphorus. 

Only about 12 percent of the acres meet the criteria for both

phosphorus and nitrogen management (table 9). 

 

19 Meeting criteria for the more strict phosphorus basis for manure application 

was not evaluated. It is a common practice to use a nitrogen basis for manure 

application, which usually results in over-application of phosphorus. The 

farmers practicing sound phosphorus management then wait to apply manure 

again when soil tests show that phosphorus is needed. This prevents 

phosphorus from building up in the soil to levels that result in significant loss 

of soluble phosphorus in surface water runoff. It was not possible to determine 

this behavior from the survey responses. 
Draft June 2010 Page 36 

Table 9. Nutrient management practices for the baseline conservation condition, Upper Mississippi River Basin 

Percent 

of acres 

without 

manure 

applied 

Percent 

of acres 

with 

manure 

applied 

Percent 

of all 

cropped 

acres 

Nitrogen* 

No N applied to any crop in rotation 3 0 2 

For samples where N is applied: 

Time of application 

All crops in rotation have application of N (manure and/or fertilizer) within 3 weeks before planting or after planting 51 11 45 

Some or all crops in rotation have fall application of N (manure and/or fertilizer) for spring planted crop 41 64 45 

Some or all crops in rotation have application of N (manure and/or fertilizer) prior to 3 weeks before planting 5 25 8 

Method of application 

All crops in rotation have N applied with incorporation or banding/foliar/spot treatment 59 42 56 

Some crops in rotation have N applied with incorporation or banding/foliar/spot treatment 34 57 38 

No crops in rotation have N applied with incorporation or banding/foliar/spot treatment 5 1 4 

Rate of application 

All crops in rotation have N applied at a rate less than 1.4 times the removal in the yield at harvest 33 36 34 

Some crops in rotation have N applied at a rate less than 1.4 times the removal in the yield at harvest 59 56 58 

No crops in rotation have N applied at a rate less than 1.4 times the removal in the yield at harvest 5 8 6 

Timing and method and rate of application 

All crops have N rate less than 1.4 times removal at harvest and application within 3 weeks before planting or after 

planting with incorporation or banding/foliar/spot treatment 17 2 14 

Some crops have N rate less than 1.4 times removal at harvest or application within 3 weeks before planting or after 

planting or use of incorporation or banding/foliar/spot treatment 70 71 70 

No crops have N rate less than 1.4 times removal at harvest or application within 3 weeks before planting or after 

planting or use of incorporation or banding/foliar/spot treatment 11 27 14 

 

Phosphorus* 

No P applied to any crop in rotation 1 0 1 

For samples where P is applied: 

Time of application 

All crops in rotation have application of P (manure and/or fertilizer) within 3 weeks before planting or after planting 57 13 50 

Some or all crops in rotation have fall application of P (manure and/or fertilizer) for spring planted crop 36 63 41 

Some or all crops in rotation have application of P (manure and/or fertilizer) prior to 3 weeks before planting 6 24 9 

Method of application 

All crops in rotation have P applied with incorporation or banding/foliar/spot treatment 59 48 57 

Some crops in rotation have P applied with incorporation or banding/foliar/spot treatment 35 51 38 

No crops in rotation have P applied with incorporation or banding/foliar/spot treatment 5 1 4 

Rate of application 

Crop rotation has P applied at a rate less than 1.1 times the removal of P in the yield at harvest for the crop rotation 62 29 57 

Crop rotation has P applied at a rate more than 1.1 times the removal of P in the yield at harvest for the crop rotation 37 71 43 

Timing and method and rate of application 

Crop rotation has P rate less than 1.1 times removal at harvest and applications within 3 weeks before planting or after 

planting with incorporation or banding/foliar/spot treatment 34 2 29 

Crop rotation has P rate less than 1.1 times removal at harvest and some crops had application within 3 weeks before 

planting or after planting and/or some crops used incorporation or banding/foliar/spot treatment 27 24 26 

Crop rotation has P rate more than 1.1 times removal at harvest or no crops had applications within 3 weeks before 

planting or after planting or no crops used incorporation or banding/foliar/spot treatment 39 74 45 

 

Nitrogen and Phosphorus 

 

Crop rotation P rate less than 1.1 and N rate less than 1.4 times removal at harvest and all applications within 3 weeks 

before planting or after planting with incorporation or banding/foliar/spot treatment 14 1 12 

 

Crop rotation P rate less than 1.1 and N rate less than 1.2 times removal at harvest and all application within 3 weeks 

before planting or after planting with incorporation or banding/foliar/spot treatment 9 0 7 

 

All sample points 100 100 100 

Note: About 16 percent of cropped acres (9.5 million acres) have manure applied. 

* Adjustments were made to the reported data on nitrogen and phosphorus application rates reported in 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, is a 

function of nitrogen and phosphorus, it was necessary to add additional nitrogen and phosphorus when the reported levels were insufficient to support reasonable crop 

yields throughout the 47 years in the model simulation. The approach taken was to first identify crop samples that have application rates recorded erroneously or were 

under-reported in the survey. The model was used to identify these samples by running the simulation at optimal levels of nitrogen and phosphorus for crop growth. The 

set of crop samples identified were treated as if they had missing data. Additional nitrogen or phosphorus was added to these crop samples so that the total nitrogen or 

phosphorus use was similar to that for the unadjusted set of crop samples. About 22 percent of the acres received a nitrogen adjustment for one or more crops. About 46 

percent of the acres received a phosphorus adjustment for one or more crops. Nitrogen and phosphorus were added by increasing the existing applications (thus 

preserving the reported timing and methods), when present, or were applied at plant. 

Note: Percents may not add to 100 because of rounding. 
Draft June 2010 Page 37 

Four levels of treatment for nitrogen and phosphorus 

management were derived for use in evaluating the adequacy 

of nutrient management in the region. These treatment levels 

are combined with soil risk classes to estimate acres that 

appear to be under-treated in chapter 6. Criteria for the 

treatment levels are presented in figures 11 and 12. The high 

treatment level represents consistent use of appropriate rate, 

timing, and method for all crops. The high level of treatment 

for nitrogen additionally requires that application rates be 

equal to or less than 1.2 times the removal of nitrogen in crop 

yield at harvest to correspond to the higher standard simulated 

in the treatment scenarios presented in Chapter 7. 

Based on these treatment levels, about 9 percent of the acres in 

the UMRB have a high level of nitrogen management and 

about 29 percent have a high level of phosphorus management 

(figures 11 and 12). Few acres with manure applied meet the 

criteria for the high treatment levels. About two-thirds of 

cropped acres have either low or moderate levels of nitrogen 

management, and 43 percent of the acres have either low or 

moderate levels of phosphorus management. 

Figure 11. Conservation treatment levels for nitrogen management, baseline conservation condition, UMRB 

Criteria for four levels of nitrogen management are: 

 High treatment: All crops have (1) total nitrogen application rates (including manure) less than 1.2 times the nitrogen in the crop 

yield, (2) all applications occur within 3 weeks before planting or after planting, and (3) all applications are incorporated or 

banding/foliar/spot treatment is used. These criteria apply to both manure and commercial fertilizer applications. 

 Moderately high treatment: Total nitrogen application rates (including manure) are less than 1.4 times the nitrogen in the crop 

yield for all crops. Timing and method of application criteria may not be met. 

 Moderate treatment: All crops meet either the above criteria for timing or method, but do not meet criteria for rate. 

 Low treatment: Some or all crops in rotation exceed criteria for rate and either timing or method. 

Low Moderate Moderately high High

Manure applied 6.1 4.3 5.7 0.2

No manure applied 14.8 38.7 21.1 9.1

0

5

10

15

20

25

30

35

40

45

50

Percent of cropped acres
Draft June 2010 Page 38 

Figure 12. Conservation treatment levels for phosphorus management, baseline conservation condition, UMRB 

Criteria for four levels of phosphorus management are: 

 High treatment: (1) total phosphorus application rates (including manure) summed over all crops are less than 1.1 times the 

phosphorus in the crop yields for the crop rotation, (2) all applications occur within 3 weeks before planting or after planting, and 

(3) all applications are incorporated or banding/foliar/spot treatment was used. (Note that phosphorus applications for individual 

crops could exceed 1.1 times the phosphorus in the crop yield but total applications for the crop rotation could not.) 

 Moderately high treatment: Total phosphorus application rates (including manure) are less than 1.1 times the phosphorus in the 

crop yield for the crop rotation. No application rate or timing of application criteria is applied. 

 Moderate treatment: Sample points that do not meet the high or moderately high criteria but all phosphorus applications for all 

crops have appropriate time and method of application. 

 Low treatment: All remaining sample points. All sample points have excessive application rates over the crop rotation and 

inadequate method or timing of application for at least one crop in the rotation. 

Pesticide Management Practices 

The presence or absence of pesticide management practices 

was based on an Integrated Pest Management (IPM) indicator 

developed using producer responses to the set of IPM-related 

questions in the NRI-CEAP Cropland Survey, as discussed in 

chapter 2. Producer responses are summarized in table 10. 

Four categories of IPM activities were scored separately: (1) 

prevention, (2) avoidance, (3) monitoring, and (4) suppression. 

After normalizing the scores for each category, the categories 

were combined into a single IPM score using a weight of 1/6 

for prevention, 1/6 for avoidance, 1/3 for monitoring, and 1/3 

for suppression. An IPM indicator score greater than 50 

defined sample points with a high level of IPM activity for 

cropping systems in the UMRB. Sample points with an IPM 

indicator score of 25 to 50 were classified as moderately high 

IPM treatment and sample points with an IPM score less than 

25 were classified as low IPM treatment. Pest monitoring 

activities were the principle determinate of the IPM indicator 

score; suppression activities had the least influence on the IPM 

indicator score in the UMRB. 

About 10 percent of the acres in the UMRB have a high level 

of IPM activity (figure 13). About 54 percent have a moderate 

level of IPM activity, and 36 percent have a low level of IPM 

activity. 

Low Moderate Moderately high High

Manure applied 10.9 0.7 4.3 0.4

No manure applied 23.6 7.5 23.7 28.8

0

5

10

15

20

25

30

35

40

Percent of cropped acres
Draft June 2010 Page 39 

Table 10. Summary of survey responses to pest management questions, Upper Mississippi River Basin 

Survey question* Score 

Number samples 

with “yes” 

response 

Percent of 

cropped 

acres 

Prevention 

Pesticides with different modes action rotated or tank mixed to prevent resistance 5 1,298 37 

Chop, spray, mow, plow, burn field edges, etc. 5 1,502 42 

Clean field implements after use 5 1,205 32 

Highest possible score for prevention 15 

Avoidance 

Rotate crops to manage pests 8 2,877 77 

Use minimum till or no-till to manage pests 6 1,864 50 

Choose crop variety that is resistant to pests 6 1,550 44 

Planting locations selected to avoid pests 3 333 10 

Plant/harvest dates adjusted to manage pests 1 232 7 

Highest possible score for avoidance 24 

Monitoring 

Scouting practice: general observations while performing routine tasks 2 1,506 40 

Scouting practice: deliberate scouting 10 1,830 50 

 --Established scouting practice used 4 614 18 

 --Scouting due to pest development model 2 345 9 

 --Scouting due to pest advisory warning 2 553 16 

Scouting done by: (only highest of the 4 scores is used) 

 --Scouting by operator 2 1,306 35 

 --Scouting by employee 2 27 1 

 --Scouting by chemical dealer 1 356 10 

 --Scouting by crop consultant or commercial scout 4 181 5 

Scouting records kept to track pests? 4 683 20 

Scouting data compared to published thresholds? 4 1,103 32 

Diagnostic lab identified pest? 2 157 5 

Weather a factor in timing of pest management practice 2 1,411 37 

Highest possible score for monitoring 34 

Suppression 

Pesticides used? 0 3,622 98 

Weather data used to guide pesticide application 2 2,454 66 

Pesticides with different mode of action rotated or tank mixed to prevent resistance 5 1,298 37 

Pesticide application decision factor (one choice only): 

--Routine treatments or preventative scheduling 0 2,174 58 

--Comparison of scouting data to published thresholds 3 177 5 

--Comparison of scouting data to operator's thresholds 2 286 8 

--Field mapping or GPS 2 6 <1 

--Dealer recommendations 2 660 17 

--Crop consultant recommendations 4 115 3 

--University extension recommendations 3 4 <1 

--Neighbor recommendations 0 1 <1 

--"Other" 0 60 2 

Maintain ground covers, mulch, or other physical barriers 4 1,273 36 

Adjust spacing, plant density, or row directions 4 663 19 

Cultivate for weed control during the growing season 2 499 16 

Risk level of suite of pesticides used, based on human toxicities 

Risk in lowest 1/3 of acres 10 1,226 34 

Risk in middle 1/3 of acres 5 1,224 33 

Risk in highest 1/3 of acres 0 1,213 33 

Risk level of suite of pesticides used, based on aquatic ecosystem toxicities 

Risk in lowest 1/3 of acres 10 1,222 33 

Risk in middle 1/3 of acres 5 1,284 34 

Risk in highest 1/3 of acres 0 1,197 33 

Highest possible score for suppression 41 

Note: The scores shown in this table were used to develop an IPM indicator, as discussed in the text. 

 
Draft June 2010 Page 40 

Figure 13. Integrated Pesticide Management indicator for the baseline conservation condition, UMRB 

Note: The Integrated Pest Management (IPM) indicator was developed using responses to questions in the NRI-CEAP Cropland 

survey on pest and pesticide management 

36.2

53.7

10.1

0

10

20

30

40

50

60

Low Moderate High

Percent of cropped acres
Draft June 2010 Page 41 

Conservation Cover Establishment 

Establishing long-term cover of grass, forbs, or trees on a site 

provides the maximum protection against soil erosion. 

Conservation cover establishment is often used on cropland 

with soils that are vulnerable to erosion or leaching. The 

practice is also effective for sites that are adjacent to 

waterways, ponds, and lakes. Because these covers do not 

require annual applications of fertilizer and pesticides, this 

long-term conserving cover practice greatly reduces the loss of 

nitrogen and phosphorus from the site, and nearly eliminates 

pesticide loss. Because conservation covers are not harvested, 

they generate organic material that decomposes and increases 

soil organic carbon. 

For this study, the effect of a long-term conserving cover 

practice was estimated using acres enrolled in the General 

Signup of the CRP. The CRP General Signup is a voluntary 

program in which producers with eligible land enter into 10- 

to 15-year contracts to establish long-term cover to reduce soil 

erosion, improve water quality, and enhance wildlife habitat. 

Landowners receive annual rental payments and cost-share 

assistance for establishing and maintaining permanent 

vegetative cover. To be eligible for enrollment in the CRP 

General Signup, the field (or tract) must meet specified crop 

history criteria. 

Other factors governing enrollment in the CRP include natural 

resource-based eligibility criteria, an Environmental Benefits 

Index (EBI) used to compare and rank enrollment offers, 

acreage limits, and upper limits on the proportion of a 

county’s cropland that can be enrolled (USDA Farm Service 

Agency 2004; Wiebe and Gollehon 2006). Initially, the 

eligibility criteria included only soil erosion rates and inherent 

soil erodibility. During the 1990s and to date, the eligibility 

criteria have continued to evolve, with increasing emphasis 

placed on issues other than soil erodibility. For contract offer 

ranking, weight was given to proposals that also benefited 

wildlife, air and water quality, and other environmental 

concerns. 

As of 2006, about 32 million acres were enrolled in the CRP 

General Signup nationally, including about 2.8 million in the 

UMRB (table 11). Approximately two-thirds of the cropland 

acres enrolled in the CRP in the UMRB are classified as 

highly erodible land. The inclusion of non- highly erodible 

land is due to both the expansion of enrollment eligibility 

criteria beyond soil erosion issues and the fact that farmers 

were allowed to enroll entire fields in the CRP if a specified 

portion of the field (varied by signup and eligibility criterion) 

met the criteria. 

About 70 percent of CRP-enrolled acres in the UMRB are 

planted to introduced grasses, about 6 percent to trees, and the 

remaining 24 percent to either native grasses or plant 

communities suitable for wildlife habitat (table 11). 

Table 11. CRP General Signup acres (1,000s) included in the model simulation for the Upper Mississippi River Basin 

Signup 

# Signup date 

Introduced 

grass 

Native 

grass Trees 

Softwood

trees

Hardwood

trees

Wildlife 

habitat All 

Percent 

of CRP 

 NonHEL HEL Percent 

HEL 

5-11 prior to 1992 111.0 17.5 11.2 0 8.5 0 148.2 5 59.2 89.0 60.1 

12 06/15–06/26/92 147.3 8.1 11.0 0 3.4 6.9 176.7 6 33.4 143.3 81.1 

13 09/11–09/22/95 147.4 3.9 8.3 0 2.3 1.4 163.3 6 43.1 120.2 73.6 

15 03/03–03/28/97 708.4 90.1 33.6 0 4.8 23.1 860.0 31 209.4 650.6 75.7 

16 10/14–11/14/97 381.5 68.4 28.3 0.6 14.8 122.7 616.3 22 211.8 404.5 65.6 

18 10/26–12/11/98 260.5 43.2 11.6 0 9.5 107.7 432.5 15 181.3 251.2 58.1 

20 01/18–02/11/00 178.1 107.1 7.7 0 13.3 98.5 404.7 14 190.3 214.4 53.0 

 Total 1,934.2 338.3 111.7 0.6 56.6 360.3 2,801.7 100 928.5 1,873.2 66.9 

 Percent 69 12 4 <1 2 13 100 

 
Draft June 2010 Page 42 

Chapter 4 

Onsite (Field-Level) Effects of 

Conservation Practices 

Water 

Water is a potent force that interacts with or drives almost all 

environmental processes acting within an agricultural 

production system. The hydrologic conditions prevalent in the 

UMRB are critical to understanding the estimates of sediment, 

nutrient, and pesticide loss presented in subsequent sections. 

The APEX model simulates hydrologic processes at the field 

scale—precipitation, irrigation, evapotranspiration, surface 

water runoff, infiltration, and percolation beyond the bottom 

of the soil profile. 

Precipitation and irrigation are the sources of water for a field. 

Annual precipitation over the 47-year simulation averaged 

about 33.6 inches in this region (table 12). (Also see figure 8.) 

Only about 2.5 percent of the cultivated cropland acres are 

irrigated, at an average annual application of 9.3 inches. 

Most of the water that leaves the field is lost through 

evaporation and transpiration (evapotranspiration). On 

average, about two-thirds of the water loss from cultivated 

cropland and land in long-term conserving cover in the UMRB 

is through evapotranspiration (table 12). Evapotranspiration 

losses vary, however, according to soil characteristics and land 

cover. For most acres in the UMRB, evapotranspiration ranges 

from 60 to 80 percent of the total amount of water that leaves 

the field (figure 14). 

Loss of water through subsurface flow pathways is the second 

largest source of water loss at an average of about 6.7 inches 

per year for cropped acres and 9.5 inches per year for land in 

long-term conserving cover. Subsurface flow pathways 

include: (1) percolation through the soil profile, (2) subsurface 

flow into a tile or ditch drainage system, (3) groundwater 

return flow, (4) lateral subsurface outflow, and (5) quickreturn subsurface flow. The percentage of water loss 

represented by subsurface flow averages about 20 percent for 

cropped acres and 28 percent for land in long-term conserving 

cover. However, this percentage is highly variable for cropped 

acres in the UMRB, as shown in figure 14. 

Surface water runoff averages about 12 percent of water loss 

from fields for cropped acres and 5 percent for land in longterm conserving cover (table 12). The percentage ranges from 

zero to about 30 percent for cropped acres in the UMRB 

(figure 14). 

Structural water erosion control practices, residue 

management practices, and reduced tillage slow the flow of 

surface water runoff and allow more of the water to infiltrate 

into the soil. Model simulations indicate that conservation 

practices have reduced surface water runoff by about 0.8 inch 

per year averaged over all acres, representing a 16-percent 

reduction for the region (table 12). 

The re-routing of surface water to subsurface flow is shown 

graphically in figures 15, 16, and 17 for cropped acres. The 

amount of surface water runoff varies from acre to acre, 

ranging from an annual average of zero for some acres to 

about 10 inches per year. Surface water runoff is highest for 

acres with higher slopes, soil properties conducive to runoff, 

and higher precipitation. Similarly, subsurface flows vary 

from acre to acre (figure 16). The no-practice scenario curves 

in figures 15 and 16 show what the distribution of surface 

water runoff and subsurface flows would be if there were no 

conservation practices—less subsurface flow and more surface 

water runoff. 

Model simulations further show that land in long-term 

conserving cover (baseline conservation condition) in the 

region has, on average, about half the surface water runoff and 

nearly 50 percent more subsurface flow than would occur if 

the land was cropped (table 12). The distribution of surface 

water runoff for the baseline conservation condition and the 

no-practice scenario (simulating a cropped condition) for acres 

in long-term conserving cover are compared in figure 18. 

The variability in the effects of conservation practices in rerouting surface water to subsurface flow is shown in figure 17 

for cropped acres and figure 19 for land in long-term 

conserving cover. This variability reflects different levels of 

conservation treatment as well as differences in precipitation 

and inherent differences among acres for water to run off. 

Reductions in surface water runoff reduce the loss of nutrients 

and pesticides exported to the surrounding environment 

through overland flow. However, the increase in infiltration 

also re-directs nutrients and pesticides in solution to 

subsurface loss pathways. Consequently, careful management 

of nutrients and pesticides is required to offset this re-routing 

of pollutants when water erosion control practices are used. 
Draft June 2010 Page 43 

Figure 14. Cumulative distributions of the proportion of water lost through three loss pathways 

Table 12. Field-level effects of conservation practices on water loss pathways for cultivated cropland in the Upper Mississippi River 

Basin 

Model simulated outcome 

Baseline 

conservation 

condition 

No-practice 

scenario 

Reduction 

due to 

practices 

Percent 

reduction 

Cropped acres (58.2 million acres) 

Water sources 

Non-irrigated acres 

Average annual precipitation (inches) 33.6 33.6 0.0 0 

Irrigated acres* 

Average annual precipitation (inches) 33.1 33.1 0.0 0 

Average annual irrigation water applied (inches) 9.3 17.3 7.9 46 

Water loss pathways 

Average annual evapotranspiration (inches) 23.4 23.5 0.1 1 

Average annual surface water runoff (inches) 4.0 4.8 0.8 16 

Average annual subsurface water flow (inches)** 6.7 5.8 -0.9*** -15 

 

Land in long-term conserving cover (2.8 million acres) 

Water sources 

Average annual precipitation (inches) 33.8 33.8 0.0 0 

Average annual irrigation water applied (inches)* 0.0 0.2 0.2 100 

Water loss pathways 

Average annual evapotranspiration (inches) 22.8 23.2 0.4 2 

Average annual surface water runoff (inches) 1.8 4.6 2.8 60 

Average annual subsurface water flow (inches)** 9.5 6.1 -3.4 -56 

* Only 2.5 percent of the cropped acres in the UMRB are irrigated. Land in long-term conserving cover was not irrigated, but some farming practices used to simulate a 

cropped condition to represent the no-practice scenario included irrigation. Values shown in the table for land in long-term conserving cover are averages over all acres, 

including non-irrigated acres. 

** Subsurface flow pathways include (1) percolation through the soil profile, (2) subsurface flow into a drainage system, (3) groundwater return flow, (4) lateral 

subsurface outflow, and (5) quick-return subsurface flow. 

*** Represents an average gain in subsurface flow of 0.9 inch per year (15 percent increase) due to the use of 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 C for the 14 subbasins. 

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 10 20 30 40 50 60 70 80 90 100

Proportion of water loss pathways

Cumulative percent acres

Subsurface flow Surface water runoff Evapotranspiration
Draft June 2010 Page 44 

Figure 15. Estimates of average annual surface water runoff for cropped acres in the Upper Mississippi River Basin 

Figure 16. Estimates of average annual subsurface flow for cropped acres in the Upper Mississippi River Basin 

0

1

2

3

4

5

6

7

8

9

10

11

12

0 10 20 30 40 50 60 70 80 90 100

Average annual surface water runoff (inches)

Cumulative percent acres

Baseline conservation condition No-practice scenario

0

2

4

6

8

10

12

14

16

18

20

0 10 20 30 40 50 60 70 80 90 100

Average annual subsurface water runoff (inches)

Cumulative percent acres

Baseline conservation condition No-practice scenario
Draft June 2010 Page 45 

Figure 17. Estimates of average annual reduction in surface water runoff due to the use of conservation practices on cropped acres in 

the Upper Mississippi River Basin 

Note: About 4 percent of the acres had less surface water runoff in the no-practice scenario than the baseline conservation condition. In general, these gains in surface 

water runoff due to practices occur on soils with low to moderate potential for surface water runoff together with (1) higher nutrient application rates in the no-practice 

scenario that result in more biomass production, which can reduce surface water runoff (typically rotations with hay or continuous corn); or (2) the additional tillage 

simulated in the no-practice scenario provided increased random roughness of the surface reducing runoff on nearly level landscapes with low crop residue rotations. 

 

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0 10 20 30 40 50 60 70 80 90 100

Average annual reduction in surface water runoff 

(inches)

Cumulative percent acres
Draft June 2010 Page 46 

Cumulative Distributions Show How Effects of Conservation Practices Vary 

Throughout the Region

The design of this study provides the opportunity to examine not only the overall mean value for a given 

outcome, but also the entire distribution of outcomes. This is possible because outcomes are estimated for 

each of the 3,703 sample points used to represent cropped acres in the UMRB and for each of the 1,831 

sample points used to represent land in long-term conserving cover. Cumulative distributions show the 

full set of estimates and thus demonstrate how conditions and the effects of conservation practices vary 

throughout the region. 

Cumulative distributions shown in this report are plots of the value for each percentile. In figure 15, for 

example, the curve for average annual surface water runoff for the baseline conservation condition 

consists of each of the percentiles of the distribution of 3,703 surface water runoff estimates, weighted by 

the acres associated with each sample point. The 10th percentile for the baseline conservation condition is 

1.9 inches per year, indicating that 10 percent of the acres have 1.9 inches or less of surface water runoff, 

on average. Similarly, the same curve shows that 25 percent of the acres have surface water runoff less 

than 2.6 inches per year. The 50th percentile—the median—is 3.6 inches per year, which in this case is 

close to the mean value of 4.0 inches per year. At the high end of the distribution, 90 percent of the acres 

in this region have surface water runoff less than 6.7 inches per year; and conversely, 10 percent of the 

acres have surface water runoff greater than 6.7 inches per year. The curves can also be used to define 

various ranges; for example, half of the cropped acres in the UMRB have average annual surface water 

runoff of 2.6-5.1 inches per year, where the range is based on the 25th and 75th percentiles. 

Thus, the distributions show the full range of outcomes for cultivated cropland acres in the UMRB. The 

full range of outcomes for the baseline condition is compared to that for the no-practice scenario in figure 

15 to illustrate the extent to which conservation practices reduce surface water runoff throughout the 

region. 

Figure 17 shows the effects of conservation practices on surface water runoff using the distribution of the 

reduction in surface water runoff, calculated as the outcome for the no-practice scenario minus the 

outcome for the baseline conservation condition at each of the 3,703 cropped sample points. This 

distribution shows that, while the mean reduction is 0.8 inch per year, 14 percent of the acres have 

reductions due to conservation practices greater than 1.3 inches per year, 6 percent of the acres have zero 

reductions (including all acres not treated for soil erosion control), and 4 percent of the acres actually 

have increases in surface water runoff (i.e., negative reductions) as a result of soil erosion control 

conservation practice use. (See footnote to figure 17 for an explanation of the conditions that result in 

gains in surface water runoff due to conservation practices.) 
Draft June 2010 Page 47 

Figure 18. Estimates of average annual surface water runoff for land in long-term conserving cover in the Upper Mississippi River 

Basin 

Figure 19. Estimates of average annual reduction in surface water runoff due to conversion to long-term conserving cover in the 

Upper Mississippi River Basin 

0

1

2

3

4

5

6

7

8

9

10

11

12

0 10 20 30 40 50 60 70 80 90 100

Average annual surface water runoff (inches)

Cumulative percent acres

Baseline conservation condition No-practice scenario

-1

0

1

2

3

4

5

6

7

8

9

0 10 20 30 40 50 60 70 80 90 100

Average annual reduction in surface water runoff 

(inches)

Cumulative percent acres
Draft June 2010 Page 48 

While the differences in the reduction of surface water runoff 

among combinations of structural practices and residue and 

tillage management are not large, residue and tillage 

management has more of an effect than structural practices on 

the re-routing of surface water to subsurface flows (table 13). 

Acres that meet criteria for no-till or mulch till and are gaining 

soil organic carbon reduce surface water flow by an average of 

17 percent, both with and without structural practices in use. 

About two-thirds of the acres in the UMRB are in these two 

treatment categories (table 13). 

Table 13. Estimates of effects of combinations of structural practices and residue and tillage management on average annual surface 

water runoff for cropped acres in the Upper Mississippi River Basin 

 Average annual surface water runoff (inches) 

Conservation treatment 

Percent of 

cropped 

acres 

Baseline 

conservation 

condition 

No-practice 

scenario 

Reduction 

due to 

practices 

Percent 

reduction 

No-till or mulch till with carbon gain, no 

structural practices 36 4.0 4.8 0.8 17 

No-till or mulch till with carbon loss, no 

structural practices 11 3.7 4.5 0.7 16 

Some crops with reduced tillage, no 

structural practices 3 3.7 4.3 0.6 14 

 

Structural practices and no-till or mulch till 

with carbon gain 35 4.0 4.8 0.8 17 

Structural practices and no-till or mulch till 

with carbon loss 8 4.4 5.2 0.8 15 

Structural practices and some crops with 

reduced tillage 1 3.9 4.4 0.4 10 

 

Structural practices only 1 4.2 4.4 0.1 3 

No water erosion control treatment 4 4.6 4.5 0.0 0 

 

All acres 100 4.0 4.8 0.8 16 

Note: Differences in slope, soil texture, hydrologic group, and precipitation for acres in different treatment groups explain some of the differences shown in this table. 

Note: Percent reductions were calculated prior to rounding the values for reporting in the table and the associated text. 

Note: Percents may not add to totals because of rounding. 

 
Draft June 2010 Page 49 

Erosion and Sediment Loss 

Wind erosion 

Wind erosion removes the most fertile parts of the soil such as 

the lighter, less dense soil constituents including organic 

matter, clays, and silts. Wind erosion occurs when the soil is 

unprotected and wind velocity exceeds about 13 miles per 

hour near the surface. Wind velocity, tillage, vegetative cover, 

and the texture and structure of the soil are primary 

determinants of wind erosion.20 

Wind erosion is a relatively minor resource concern in the 

UMRB. The greatest concern with wind erosion in the UMRB 

is crop damage to young seedlings exposed to windblown 

material. Wind erosion rates as low as 0.5 ton per acre are 

known to cause physical damage to young seedlings. 

For all cropped acres, model simulations show that the 

average annual rate of wind erosion is only 0.24 ton per acre 

(table 14). However, a few areas have persistently high rates 

of wind erosion in some years (figure 20). In the most extreme 

year included in the model simulations (representing 1967), 

wind erosion exceeded 1 ton per acre for 27 percent of the 

cropped acres in the UMRB and exceeded 2 tons per acre for 

12 percent of the acres. 

 

20 Wind erosion is estimated in APEX using the Wind Erosion Continuous 

Simulation (WECS) model. The estimated wind erosion rate is the amount of 

eroded material leaving the downwind edge of the field. 

Structural practices for wind erosion control are in use on only 

3 percent of the cropped acres in the UMRB. However, other 

practices common in the region, such as residue and tillage 

management, reduced tillage, and various water erosion 

control practices, are also effective in reducing wind erosion. 

Model simulations indicate that conservation practices have 

reduced the average wind erosion rate by 54 percent in the 

region (table 14). Model simulations show that the average 

annual rate of wind erosion exceeds 1 ton per acre on about 4 

percent of the cropped acres (figure 21). Without conservation 

practices, wind erosion would exceed 1 ton per acre on about 

13 percent of the cropped acres. Figure 22 shows that 

conservation practices have reduced wind erosion by more 

than 0.5 ton per acre on about 20 percent of the acres.

Even though wind erosion is not a major resource concern in 

the UMRB, these reductions in wind erosion rates are still 

significant, especially in areas prone to wind erosion. As 

shown in later sections, wind erosion can be responsible for 

significant loss of nitrogen and especially phosphorus from 

fields. 

Since grass or other cover has been established on land in 

long-term conserving cover, there is no wind erosion currently 

for these acres. If these acres were cropped without any 

conservation practices, the wind erosion rate on these 2.8 

million acres would average about 0.1 ton per acre per year. 
Draft June 2010 Page 50 

Table 14. Field-level effects of conservation practices on erosion and sediment loss for cultivated cropland in the Upper Mississippi 

River Basin 

Model simulated outcome 

Baseline 

conservation 

condition 

No-practice 

scenario 

Reduction 

due to 

practices 

Percent 

reduction 

Cropped acres (58.2 million acres) 

Average annual wind erosion (tons/acre) 0.24 0.52 0.28 54 

Average annual sheet and rill erosion (tons/acre)* 1.04 2.10 1.06 51 

Average annual sediment loss at edge of field due to water 

erosion (tons/acre) 0.98 3.11 2.13 69 

Highly erodible land (18 percent of cropped acres) 

Average annual wind erosion (tons/acre) 0.11 0.31 0.20 65 

Average annual sheet and rill erosion (tons/acre)* 2.38 5.07 2.69 53 

Average annual sediment loss at edge of field due to water 

erosion (tons/acre) 2.65 8.42 5.77 69 

Non-highly erodible land (82 percent of cropped acres) 

Average annual wind erosion (tons/acre) 0.27 0.57 0.30 53 

Average annual sheet and rill erosion (tons/acre)* 0.74 1.43 0.69 48 

Average annual sediment loss at edge of field due to water 

erosion (tons/acre) 0.60 1.91 1.31 69 

 

Land in long-term conserving cover (2.8 million acres) 

Average annual wind erosion (tons/acre) 0.00 0.07 0.07 100 

Average annual sheet and rill erosion (tons/acre)* 0.13 4.21 4.08 97 

Average annual sediment loss at edge of field due to water 

erosion (tons/acre) 0.06 6.56 6.50 99 

* 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: Model simulation results for the baseline conservation condition are presented in appendix C for the 14 subbasins. 
Draft June 2010 Page 51 

Figure 20. Distribution of annual wind erosion rate for each year of the 47-year model simulation, Upper Mississippi River Basin

Note: This figure shows how annual wind erosion (tons per acre per year) varied within the region and from year to year in the model simulation for cropped acres. 

Each of the 47 curves shown above represents a single year of data and shows how annual wind erosion varied over the region in that year, starting with the acres with 

the lowest rates and increasing to the acres with the highest rates. The family of curves shows how annual wind erosion rates varied from year to year. 

0

1

2

3

4

5

6

7

8

0 10 20 30 40 50 60 70 80 90 100

Annual wind erosion (tons/acre)

Cumulative percent acres
Draft June 2010 Page 52 

Figure 21. Estimates of average annual wind erosion rate for cropped acres in the Upper Mississippi River Basin 

Figure 22. Estimates of average annual reduction in wind erosion rate due to the use of conservation practices on cropped acres in the 

Upper Mississippi River Basin 

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

2.6

2.8

3.0

0 10 20 30 40 50 60 70 80 90 100

Average annual wind erosion (tons/acre)

Cumulative percent acres

Baseline conservation condition No-practice scenario

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

0 10 20 30 40 50 60 70 80 90 100

Average annual reduction in wind erosion 

(tons/acre)

Cumulative percent acres
Draft June 2010 Page 53 

Water erosion 

Sheet and rill erosion is the detachment and movement of soil 

particles within the field that occurs during rainfall events. 

Controlling sheet and rill erosion is important for sustaining 

soil productivity and preventing soil from leaving the field.

Sediment loss, as referred to in this study, is the sediment that 

is transported beyond the edge of the field by water, where the 

field includes any edge-of-field filtering and buffering 

conservation practices. Soil erosion and sedimentation are 

separate but interrelated resource concerns. Soil erosion is the 

detachment and transport of soil particles, while sedimentation 

is that portion of the eroded material that settles out in areas 

onsite or offsite. Sediment loss, as estimated in this study, 

includes the portion of the sheet and rill eroded material that 

settles offsite as well as some sediment that originates from 

gully erosion processes.21 Sediment is composed of detached 

and transported soil minerals, organic matter, plant and animal 

residues, and associated chemical and biological compounds. 

Sheet and rill erosion. Sheet and rill erosion in the UMRB 

averages about 1 ton per acre per year (table 14). Sheet and rill 

erosion rates are higher for highly erodible land, averaging 2.4 

tons per acre per year compared to the average annual rate for 

non-highly erodible land of 0.7 tons per acre. 

Model simulation results show that conservation practices 

have reduced sheet and rill erosion on cropped acres in the 

UMRB by an average of 1.0 ton per acre per year, 

representing a 51-percent reduction on average (table 14). 

While the average annual reduction in sheet and rill erosion 

for highly erodible land is almost four times that for nonhighly erodible acres (table 14), the percent reduction due to 

conservation practices is only slightly higher. 

For land in long-term conserving cover, sheet and rill erosion 

has been reduced from 4.2 tons per acre per year if cropped 

without conservation practices to about 0.1 ton per acre (table 

14). 

Sediment loss due to water erosion. The average 

annual sediment loss for cropped acres in the UMRB is 1 ton 

per acre per year, according to the model simulation (table 

14). As seen for sheet and rill erosion, sediment loss for highly 

erodible land is much higher than for non-highly erodible 

land. 

On an annual basis, sediment loss can vary considerably. 

Figure 23 shows that, with the conservation practices currently 

in use in the UMRB, annual sediment loss is below 0.1 ton per 

acre for about 20 percent of the acres under all conditions, 

including years with high precipitation. About 60 percent have 

 

21 For this study, the APEX model was set up to estimate sediment loss using 

a modified version of USLE, called MUSS, 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 gully erosion and some ephemeral gully erosion. For this 

reason, sediment loss rates can exceed sheet and rill erosion rates. 

annual sediment loss rates less than 1 ton per acre under all 

conditions. In contrast, sediment loss exceeds 4 tons per acre 

in one or more years on about 15 percent of the cropped acres. 

Model simulations indicate that the use of conservation 

practices in the UMRB has reduced average annual sediment 

loss due to water erosion by 69 percent for cropped acres in 

the region, including both treated and untreated acres (table 

14). Without conservation practices, the average annual 

sediment loss for these acres would have been 3.1 tons per 

acre per year—three times as much as the 1 ton per acre 

average for the baseline conservation condition. Figure 24 

shows that about 53 percent of the acres would have less than 

2 tons per acre per year sediment loss without practices, 

compared to 87 percent with conservation practices. 

Reductions in sediment loss due to conservation practices are 

much higher for some acres than others, reflecting both the 

level of treatment and the inherent erodibility of the soil. For 

about half of the acres, the average annual sediment loss 

reduction due to practices is less than 1 ton per acre (figure 

25). The top 10 percent of the acres had reductions in average 

annual sediment loss greater than 5.6 tons/acre. 

Acres with a combination of structural practices and residue 

and tillage management have the highest percent reduction in 

sediment loss (table 15). Acres that are treated with structural 

practices, meet tillage intensity criteria for no-till or mulch till, 

and are gaining soil organic carbon (about 35 percent of 

cropped acres) have reduced sediment loss by 84 percent, on 

average. For these treated acres, annual sediment loss averages 

about 0.7 ton per acre.

Acres in long-term conserving cover have very little erosion or 

sediment loss, and thus show nearly 100 percent reductions 

when compared to a cropped condition (table 14, figure 26). If 

these acres were still being cropped without any conservation 

practices, sediment loss would average about 6.6 tons per acre 

per year on these 2.8 million acres.

Reductions in sediment loss for land in long-term conserving 

cover compared to the same acres with crops and no 

conservation practices vary considerably, as shown in figure 

27. The average reduction over all acres in long-term 

conserving cover is 6.5 tons per acre per year. However, 27 

percent of the acres in long-term conserving cover have 

reductions of less than 2 tons per acre per year average and 

reductions greater than 10 tons per acre per year occur on 

about 25 percent of the acres. 
Draft June 2010 Page 54 

Figure 23. Distribution of annual sediment loss for each year of the 47-year model simulation, Upper Mississippi River Basin 

Note: This figure shows how annual sediment loss (tons per acre per year) varied within the region and from year to year in the model simulation for cropped acres. 

Each of the 47 curves shown above represents a single year of data and shows how annual sediment loss varied over the region in that year, starting with the acres with 

the lowest sediment loss and increasing to the acres with the highest sediment loss. The family of curves shows how annual sediment loss varied from year to year. 

 

0

2

4

6

8

10

12

14

16

0 10 20 30 40 50 60 70 80 90 100

Annual sediment loss (tons/acre)

Cumulative percent acres
Draft June 2010 Page 55 

Figure 24. Estimates of average annual sediment loss for cropped acres in the Upper Mississippi River Basin

Figure 25. Estimates of average annual reduction in sediment loss due to the use of conservation practices on cropped acres in the 

Upper Mississippi River Basin 

0

2

4

6

8

10

12

14

16

18

20

0 10 20 30 40 50 60 70 80 90 100

Average annual sediment loss (tons/acre)

Cumulative percent acres

Baseline conservation condition No-practice scenario

0

2

4

6

8

10

12

14

16

18

0 10 20 30 40 50 60 70 80 90 100

Average annual reduction in sediment loss 

(tons/acre)

Cumulative percent acres
Draft June 2010 Page 56 

Table 15. Estimates of effects of combinations of structural practices and residue and tillage management on average annual sediment 

loss for cropped acres in the Upper Mississippi River Basin 

 Average annual sediment loss (tons/acre) 

Conservation treatment 

Percent of 

cropped 

acres 

Baseline 

conservation 

condition 

No-practice 

scenario 

Reduction 

due to 

practices 

Percent 

reduction 

No-till or Mulch till with carbon gain, no 

structural practices 36 0.59 1.29 0.69 54 

No-till or mulch till with carbon loss, no 

structural practices 11 1.46 2.49 1.04 42 

Some crops with reduced tillage, no 

structural practices 3 0.83 1.19 0.36 30 

 

Structural practices and No-till or Mulch till 

with carbon gain 35 0.73 4.45 3.72 84 

Structural practices and No-till or Mulch till 

with carbon loss 8 2.41 7.27 4.85 67 

Structural practices and some crops with 

reduced tillage 1 1.03 3.32 2.29 69 

 

Structural practices only 1 1.68 4.47 2.79 62 

No water erosion control treatment 4 2.09 2.15 0.06 3 

All acres 100 0.98 3.11 2.13 69 

Note: Differences in slope, soil texture, hydrologic group, and precipitation for acres in different treatment groups account for some of the differences shown in this 

table. 

Note: Percent reductions were calculated prior to rounding the values for reporting in the table and the associated text. 

Note: Percents may not add to totals because of rounding. 
Draft June 2010 Page 57 

Figure 26. Estimates of average annual sediment loss for acres in long-term conserving cover in the Upper Mississippi River Basin 

Figure 27. Estimates of average annual reduction in sediment loss due to conversion to long-term conserving cover in the Upper 

Mississippi River Basin 

0

2

4

6

8

10

12

14

16

18

20

22

24

26

28

30

0 10 20 30 40 50 60 70 80 90 100

Average annual sediment loss (tons/acre)

Cumulative percent acres

Baseline conservation condition No-practice scenario

0

2

4

6

8

10

12

14

16

18

20

22

24

26

28

30

0 10 20 30 40 50 60 70 80 90 100

Average annual reduction in sediment loss (tons/acre)

Cumulative percent acres
Draft June 2010 Page 58 

Soil Organic Carbon 

The landscape in the UMRB is conducive to maintaining and 

enhancing soil organic carbon. The combination of gently 

sloping to level soils that tend to be moderately well drained 

or have loamy textures inherently allows the soils to withstand 

more intense tillage and maintain or enhance carbon stores 

relative to most other regions of the country. This ability is 

complemented by the high-residue crop rotations commonly 

used by farmers in the basin; over 94 percent of the acres have 

corn, small grains, or hay in the rotation. 

The estimation of soil organic carbon change is based on 

beginning soil characteristics that reflect the effects of years of 

traditional conventional tillage practices and older, lower 

yielding crop varieties. These effects generally resulted in 

soils with organic carbon levels at or near their low steady 

state. Modern high yielding crop varieties with and without 

the adoption of conservation tillage tends to readily improve 

the status of carbon in many soils, especially those with 

beginning stocks far less than the steady state representation of 

the present management. Beginning the simulations at a lower 

steady state for carbon allows for a more equitable comparison 

of conservation practices, particularly conservation tillage. 

Because of this, however, model estimates of soil organic 

carbon change may be somewhat larger than shown in other 

studies. Nevertheless, model estimates obtained in this study 

fall within the expected range for the continuum of adoption 

of new crop genetics and tillage practices. 

 

Model simulation shows that for the baseline conservation 

condition the average annual carbon change is a gain of about 

70 pounds per acre per year, on average (table 16). Without 

conservation practices, the annual change in soil organic 

carbon would average about zero pounds per acre per year, 

indicating that soil organic carbon is neither losing or gaining, 

on average for the region. 

However, average annual change in soil organic carbon varies 

considerably among acres in the region, as shown in figure 28. 

For the baseline conservation condition, about 75 percent of 

the acres are gaining soil organic carbon (figure 28); for these 

acres, the annual average gain in soil organic carbon is 138 

pounds per acre per year. If conservation practices were not in 

use, only 59 percent of the acres would be gaining soil organic 

carbon and the annual rate of gain would be only 100 pounds 

per acre per year on those acres. Acres that are losing soil 

organic carbon are diminishing in soil quality year by year. 

For land in long-term conserving cover, the gain in soil 

organic carbon for the baseline conservation condition 

averages 349 pounds per acre per year. If these acres were still 

being cropped without any conservation practices, the annual 

average change in soil organic carbon would be a loss of 70 

pounds per acre per year. 

Cropped acres that are gaining soil organic carbon every year 

provide soil quality benefits that enhance production and 

reduce the potential for sediment, nutrient, and pesticide 

losses. Soil organic carbon improves the soil’s ability to 

function with respect to nutrient cycling, improves water 

holding capacity, and reduces erodibility. 

These estimates account for losses of carbon with sediment 

removed from the field by wind and water erosion. Some of 

the increased gain in soil organic carbon due to conservation 

practices is the result of soil erosion control—keeping soil 

organic carbon on the field promotes soil quality. Loss of soil 

organic carbon due to wind and water erosion averages about 

189 pounds per acre per year for the baseline conservation 

condition (table 16). If conservation practices were not in use, 

loss of soil organic carbon due to wind and water erosion 

would average an additional 39 pounds per acre per year. 

For air quality concerns, the analysis centers on the decrease 

in CO2 emissions. Soils gaining carbon are obviously 

diminishing emissions, but so are soils that continue to lose 

carbon but at a slower rate. For all cropped acres, the 

reduction in carbon emissions for farm fields averages 70 

pounds per acre for the baseline conservation condition, 

equivalent to a CO2 emission reduction of 7.5 million U.S. 

tons of carbon dioxide. For acres in long-term conserving 

cover, the reduction in carbon emissions averages 419 pounds 

per acre compared to a cropped condition without 

conservation practices, equivalent to a CO2 emission 

reduction of 2.2 million U.S. tons of carbon dioxide. However, 

the rate of emission reduction due to conservation practices 

varies considerably among acres, as shown in figures 29 and 

30. 

As observed for sediment loss, acres with a combination of 

structural practices and residue and tillage management have 

the highest annual increases in soil organic carbon, and thus 

the highest decrease in CO2 emissions (table 17). This is due, 

in part, to reductions in erosion losses for treated acres.

 
Draft June 2010 Page 59 

Table 16. Field-level effects of conservation practices on soil organic carbon for cultivated cropland in the Upper Mississippi River 

Basin 

Model simulated outcome 

Baseline 

conservation 

condition 

No-practice 

scenario 

Reduction 

due to 

practices 

Percent 

reduction 

Cropped acres (58.2 million acres) 

Average annual loss of carbon with wind and water erosion 

(pounds/acre) 189 228 39 17 

Average annual change in soil organic carbon, including 

loss of carbon with wind and water erosion (pounds/acre) 70 0 70* -- 

 

Land in long-term conserving cover (2.8 million acres) 

Average annual loss of carbon with wind and water erosion 

(pounds/acre) 54 357 303 85 

Average annual change in soil organic carbon, including 

loss of carbon with wind and water erosion (pounds/acre) 349 -70 419* -- 

* Gain in soil organic carbon due to 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 C for the 14 subbasins. 

Table 17. Estimates of effects of combinations of structural practices and residue and tillage management on average annual soil 

organic carbon change for cropped acres in the Upper Mississippi River Basin 

 

Average annual change in soil 

organic carbon (pounds/acre) 

Gain due to 

Conservation treatment practices 

Percent of 

cropped 

acres 

Baseline 

conservation 

condition 

No-practice 

scenario 

No-till or Mulch till with carbon gain, no 

structural practices 36 133 73 60 

No-till or mulch till with carbon loss, no 

structural practices 11 -121 -168 48 

Some crops with reduced tillage, no 

structural practices 3 -6 -33 28 

 

Structural practices and No-till or Mulch till 

with carbon gain 35 148 49 100 

Structural practices and No-till or Mulch till 

with carbon loss 8 -126 -207 81 

Structural practices and some crops with 

reduced tillage 1 34 -6 40 

 

Structural practices only 1 -87 -116 29 

No water erosion control treatment 4 -136 -129 -7 

All acres 100 70 0 70 

Note: Estimates include reductions in loss of carbon from the field through wind and water erosion that are due to the use of conservation practices. Differences in 

slope, soil texture, hydrologic group, and precipitation for acres in different treatment groups explain some of the differences in sediment loss shown in this table. 

Note: Percents may not add to totals because of rounding. 
Draft June 2010 Page 60 

Figure 28. Estimates of average annual change in soil organic carbon for cropped acres in the Upper Mississippi River Basin

Figure 29. Estimates of average annual gain in soil organic carbon due to the use of conservation practices on cropped acres in the 

Upper Mississippi River Basin

Note: About 12 percent of the acres have a higher soil organic carbon increase in the no-practice scenario than the baseline conservation condition because of the higher 

fertilization rates, including manure application rates, used in the no-practice scenario to simulate the effects of nutrient management practices. Reductions in manure 

application reduce the rate of build-up of soil organic carbon. Reductions in commercial fertilizer application can also reduce the amount of residue produced when 

other conservation practices are inadequate to control losses. 

-600

-500

-400

-300

-200

-100

0

100

200

300

400

500

600

0 10 20 30 40 50 60 70 80 90 100

Average annual change in soil organic carbon 

(pounds/acre)

Cumulative percent acres

Baseline conservation condition No-practice scenario

-300

-200

-100

0

100

200

300

400

500

0 10 20 30 40 50 60 70 80 90 100

Average annual gain in soil organic carbon 

(pounds/acre)

Cumulative percent acres
Draft June 2010 Page 61 

Figure 30. Estimates of average annual gain in soil organic carbon due to conversion to long-term conserving cover in the Upper 

Mississippi River Basin 

Note: About 10 percent of the acres in long-term conserving cover have decreases in annual carbon gain compared to a cropped condition. Biomass production under 

long-term conserving cover is typically nitrogen limited. The higher biomass production and resulting crop residue from the fertilization of cropped acres can exceed 

the carbon benefits of long-term conserving cover under some conditions. 

-500

0

500

1,000

1,500

2,000

2,500

3,000

3,500

0 10 20 30 40 50 60 70 80 90 100

Average annual gain in soil organic carbon 

(pounds/acre)

Cumulative percent acres
Draft June 2010 Page 62 

Nitrogen Loss 

Plant-available nitrogen sources include application of 

commercial fertilizer, application of manure, nitrogen 

produced by legume crops (soybeans, alfalfa, beans, and 

peas), a small amount of manure deposited by grazing 

livestock, and atmospheric nitrogen deposition. In total, these 

sources provide about 152 pounds of nitrogen per acre per 

year for cropped acres in the UMRB (table 18). Model 

simulations show that about two-thirds of this (108 pounds per 

acre) is taken up by the crop and removed at harvest in the 

crop yield, on average, and the remainder is lost from the 

field. 

For the baseline conservation condition, the annual average 

amount of total nitrogen lost from the field, other than the 

nitrogen removed from the field at harvest, is about 41 pounds 

per acre. These nitrogen loss pathways are— 

 nitrogen lost due to volatilization associated with fertilizer 

and manure application (average of 6.7 pounds per acre 

per year); 

 nitrogen returned to the atmosphere through 

denitrification processes (average of 2.2 pounds per acre 

per year); 

 nitrogen lost with windborne sediment (average of 2.1 

pounds per acre per year); 

 nitrogen lost with surface runoff, including nitrogen lost 

with waterborne sediment (average of 8.6 pounds per acre 

per year); and 

 nitrogen loss in subsurface flow pathways (average of 

21.8 pounds per acre per year). 

In the model simulations for the UMRB, about two-thirds of 

the nitrogen loss in subsurface flow eventually returns to 

surface water, on average, while about one-third is carried 

with water flow that recharges the underlying aquifers. 

The percent of nitrogen lost in each loss pathway varies from 

acre to acre, as shown in figure 31. The dominant nitrogen loss 

pathway for most cropped acres (71 percent) in the UMRB is 

nitrogen loss in subsurface flow. On average for all acres in 

the region, 53 percent of the nitrogen lost from fields is 

through subsurface flow. Nitrogen volatilization or nitrogen 

lost as waterborne sediment are the next highest loss 

pathways, averaging 16 percent and 19 percent of total 

nitrogen loss, respectively. Nitrogen loss with waterborne 

sediment is the dominant loss pathway for 18 percent of the 

acres, while volatilization is the dominant loss pathway for 8 

percent of the acres. Nitrogen loss with windborne sediment is 

the dominant loss pathway for 3 percent of the acres. Nitrogen 

loss in surface water runoff (soluble) and nitrogen lost through 

denitrification are rarely the dominant loss pathways, but are 

significant loss pathways for some acres (figure 31). 

In both the baseline conservation condition and the no-practice 

scenario, average annual nitrogen losses for all loss pathways 

were higher for acres receiving manure than for acres that did 

not receive manure (table 18). Losses were also higher for 

highly erodible land than for non-highly erodible land. 

Total nitrogen loss 

Model simulations for the baseline conservation condition 

indicate that some cropped acres in the UMRB are much more 

susceptible to the effects of weather than other acres and lose 

much higher amounts of nitrogen and (figure 32). About 40 

percent of the acres lose less than 40 pounds per acre per year 

through the various loss pathways other than removal at 

harvest under all weather conditions. About 20 percent of the 

acres, on the other hand, lose more than 100 pounds per acre 

in at least some years. Figure 32 also shows that nitrogen loss 

for the 20 percent of the cropped acres with the highest losses 

varies dramatically from year to year when compared to the 40 

percent with the lowest total nitrogen loss. Figure 32 further 

shows that, in the UMRB, total nitrogen loss from cropped 

acres can exceed 40 pounds per acre in most years on about 

one-fourth of the acres. 

Model simulations show that the conservation practices in use 

in the region have reduced total nitrogen loss from cropped 

acres (exclusive of nitrogen removed at harvest with the crop 

yield) by an average of 9 pounds per acre per year, 

representing an 18 percent reduction, on average (table 18). 

Without conservation practices, about 53 percent of the 

cropped acres would have average annual total nitrogen loss 

exceeding 40 pounds per acre per year; with conservation 

practices, only 35 percent of acres exceed this level of loss 

(figure 33). About 30 percent of the acres have average annual 

reductions in total nitrogen loss below 2 pounds per acre 

(figure 34). 

A small number of acres (13 percent) have reduced total 

nitrogen loss by an average of over 20 pounds per acre per 

year (figure 34). These are acres with higher levels of 

treatment, including acres with higher levels of nitrogen use 

and thus more nitrogen available to be reduced by practices. 

For example, the 16 percent of acres with manure applied had 

total nitrogen reductions averaging 19 pounds per acre per 

year, nearly three times the average reduction for acres that 

did not receive manure (table 18). Similarly, the average 

reduction in total nitrogen loss on highly erodible land is over 

twice that for non-highly erodible land (table 18). 

Figure 34 also shows that about 20 percent of the acres have 

an increase in total nitrogen loss due to conservation practice 

use; some of these gains are small, but 13 percent of the acres 

have gains of more than 2 pounds per acre. This result 

primarily occurs on soils with relatively high soil nitrogen 

content and generally with low slopes where the surface water 

runoff is re-directed to subsurface flow by soil erosion control 

practices. The higher volume of water moving through the soil 

profile extracts more nitrogen from the soil than under 

conditions without conservation practices. Cropping systems 

that include legumes also have a higher soil nitrogen stock in 

the baseline conditions because legumes produce 

proportionately less biofixation of nitrogen under the higher 

fertilization rates simulated in the no-practice scenario. The 

baseline conservation condition represents a wide range of 

conservation adoption. Adoption of soil erosion control 

practices without also adopting sound nutrient management 

has a negative impact on nitrogen loss. 
Draft June 2010 Page 63 

Table 18. Field-level effects of conservation practices on nitrogen sources and nitrogen loss pathways for cropped acres in the Upper 

Mississippi River Basin 

Average annual values in pounds per acre 

Model simulated outcome 

Baseline 

conservation 

condition 

No-practice 

scenario 

Reduction 

due to 

practices 

Percent 

reduction 

Cropped acres (58.2 million acres) 

Nitrogen sources 

 Atmospheric deposition 6.0 6.0 0.0 0 

 Bio-fixation by legumes 57.9 56.1 -1.8 -3 

Nitrogen applied as commercial fertilizer and manure 87.8 99.2 11.4 11 

All nitrogen sources 151.7 161.4 9.6 6 

Nitrogen loss pathways 

 Nitrogen in crop yield removed at harvest 107.6 112.9 5.4* 5* 

 Nitrogen loss by volatilization 6.7 6.5 -0.2** -4** 

 Nitrogen loss through denitrification processes 2.2 2.0 -0.2 -10 

 Nitrogen lost with windborne sediment 2.1 3.3 1.2 37 

 Nitrogen loss with surface runoff , including waterborne sediment 8.6 15.9 7.3 46 

 Nitrogen loss in subsurface flow pathways 21.8 22.8 1.0 5 

 Total nitrogen loss for all pathways except harvest 41.3 50.5 9.1 18 

 Change in soil nitrogen 1.8 -2.9 -4.7 -- 

Highly erodible land (18 percent of cropped acres) 

All nitrogen sources 157.4 166.3 8.9 5 

 Total nitrogen loss for all pathways except harvest 50.1 66.2 16.1 24 

Non-highly erodible land (82 percent of cropped acres) 

All nitrogen sources 150.5 160.3 9.8 6 

 Total nitrogen loss for all pathways except harvest 39.4 46.9 7.5 16 

Acres with manure applied (16 percent of cropped acres) 

All nitrogen sources 178.3 199.0 20.7 10 

 Total nitrogen loss for all pathways except harvest 61.8 81.2 19.4 24 

Acres without manure applied (84 percent of cropped acres) 

All nitrogen sources 146.6 154.0 7.5 5 

Total nitrogen loss for all pathways except harvest 37.4 44.5 7.1 16 

 

Land in long-term conserving cover (2.8 million acres) 

Nitrogen sources 

 Atmospheric deposition 5.9 5.9 0.0 0 

 Bio-fixation by legumes 11.7 57.2 45.6 80 

Nitrogen applied as commercial fertilizer and manure 0.0 97.8 97.8 100 

All nitrogen sources 17.6 160.9 143.3 89 

Nitrogen loss pathways 

 Nitrogen in crop yield removed at harvest 1.1*** 108.5 107.4 99 

 Nitrogen loss by volatilization 7.5 6.6 -0.9 -13 

 Nitrogen lost with windborne sediment 0.0 0.4 0.4 100 

 Nitrogen loss through denitrification processes 1.4 2.9 1.4 50 

 Nitrogen loss with surface runoff , including waterborne sediment 1.1 28.9 27.8 96 

 Nitrogen loss in subsurface flow pathways 1.7 22.7 21.0 92 

 Total nitrogen loss for all pathways except harvest 11.7 61.5 49.8 81 

 Change in soil nitrogen 4.2 -9.9 -14.1 -- 

* The reduction in yield reflects the increase in nutrients in the representation in the no-practice scenario for nutrient management. 

** On about half of the cropped acres, more nitrogen volatilization occurs with practices than without practices, resulting in a small net gain in nitrogen volatilization 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 it is exposed to wind and weather conditions that promote volatilization. 

*** Harvest was simulated on acres planted to trees where expected tree age is less than the 47-years included in the model simulation. At tree harvest time, the grass 

also is removed and replanted. 

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 C for the 14 subbasins. 
Draft June 2010 Page 64 

Figure 31. Cumulative distributions of the proportion of nitrogen lost through various loss pathways

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 10 20 30 40 50 60 70 80 90 100

Proportion of nitrogen loss pathways

Cumulative percent acres

Waterborne sediment Surface water runoff (soluble)

Subsurface flow Windborne sediment

Volatilization Denitrification
Draft June 2010 Page 65 

Figure 32. Distribution of annual total nitrogen loss for each year of the 47-year model simulation, Upper Mississippi River Basin 

Note: This figure shows how annual total nitrogen loss (pounds per acre per year) varied within the region and from year to year in the model simulation for cropped 

acres. Each of the 47 curves shown above represents a single year of data and shows how annual total nitrogen loss varied over the region in that year, starting with the 

acres with the lowest total nitrogen loss and increasing to the acres with the highest total nitrogen loss. The family of curves shows how annual total nitrogen loss varied 

from year to year. 

0

20

40

60

80

100

120

140

160

180

200

220

240

0 10 20 30 40 50 60 70 80 90 100

Annual total nitrogen loss (pounds/acre)

Cumulative percent acres
Draft June 2010 Page 66 

Figure 33. Estimates of average annual total nitrogen loss for cropped acres in the Upper Mississippi River Basin 

Figure 34. Estimates of average annual reduction in total nitrogen loss due to the use of conservation practices on cropped acres in the

Upper Mississippi River Basin 

Note: See text for discussion of conditions that result in lower total nitrogen loss in the no-practice scenario than in the baseline conservation condition for 20 percent of 

the acres. 

0

20

40

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Draft June 2010 Page 67 

Total nitrogen loss has been reduced by about 81 percent on 

the 2.8 million acres in long-term conserving cover, compared 

to the conditions that would be expected had the acres 

remained in crops. Converting cropped acres to long-term 

conserving cover is very effective in reducing total nitrogen 

loss, as demonstrated in figures 35 and 36 and table 18, 

although the reductions are much higher for some acres than 

others. Half of the acres in long-term conserving cover have 

reductions of more than 40 pounds of nitrogen loss per acre 

per year, compared to a cropped condition. 

Nitrogen lost with surface runoff 

The bulk of the reduction in total nitrogen loss for cropped 

acres is due to reductions in nitrogen lost with surface runoff, 

including both nitrogen attached to sediment and in solution 

(mineral and organic nitrogen). Model simulations show that, 

on average, nitrogen lost with surface runoff has been reduced 

46 percent due to use of conservation practices in the region 

(table 18). Without conservation practices, about 36 percent of 

the cropped acres would have nitrogen lost with surface runoff 

in excess of an average of 15 pounds per acre per year, 

compared to only 15 percent of the acres in the baseline 

conservation condition (figure 37). 

Figure 38 shows, however, that about half of the acres have 

reductions of nitrogen lost with surface runoff less than 5 

pounds per acre due to conservation practices. 

Nitrogen loss in subsurface flow 

Conservation practices had little effect on nitrogen loss in 

subsurface flow in the UMRB, as shown in figure 39. Figure 

40 shows that reductions in nitrogen loss in subsurface flow 

occur for only 47 percent of the acres; on the remaining 53 

percent of the acres nitrogen loss in subsurface flow increased 

as a result of conservation practices. (Gains in nitrogen loss in 

subsurface flow are represented in figure 40 as negative 

reductions.) 

For the region as a whole, model simulations show that 

conservation practices reduced nitrogen loss in subsurface 

flow an average of only 1 pound per acre per year, 

representing a 5 percent reduciton (table 18), on average. This 

is largely due to relatively weak nutrient management 

practices on acres with erosion control treatment. 

A portion of the reduction in nitrogen lost with surface runoff 

was re-routed to subsurface loss pathways, resulting in gains 

or only small reductions in nitrogen loss in subsurface flow. 

On many acres, the re-routing of surface water runoff to 

subsurface flow pathways resulted in additional nitrogen being 

leached from the soil, diminishing and sometimes offsetting 

the overall positive effects of conservation practices on total 

nitrogen loss. 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 will provide the environmental 

protection needed. 

 
Draft June 2010 Page 68 

Tradeoffs in Conservation Treatment 

Conservation practices applied on cropland are, for the most part, synergistic. The benefits accumulate as more practices are added to 

the designed systems. However, when only a single resource concern is addressed (such as soil erosion), antagonism between the 

practices and other resource concerns may occur. That is why it is essential that all resource concerns be considered during the 

conservation planning process. Most of the time the tradeoffs are much smaller than the magnitude of the primary resource concerns. 

Common examples are: 

 Terraces and conservation tillage are planned to solve a serious water erosion problem. However, in some areas there may be 

concern about saline seeps at the lower part of the field. The planned practices will solve the erosion problem, but could 

exacerbate the saline seep problem under some conditions. Ignoring that fact does not make for an adequate conservation plan. 

 Conservation tillage is planned for erosion control on a cropland field with a high water table. The reduction in runoff may 

increase leaching of nitrates into the shallow water table. This potential secondary problem requires additional nutrient 

management practices to address the concern. 

 A nutrient management plan reduces the amount of manure added to a field to reduce the loss of nutrients to surface or 

groundwater. However, the reduction in organic material added to the field may reduce the soil organic matter or reduce the rate 

of change in soil organic matter. 

 Figure 34 shows that about 20 percent of the acres have an increase in total nitrogen loss due to conservation practice use. This 

result occurs primarily on soils with relatively high soil nitrogen content and generally low slopes where the surface water runoff 

is re-directed to subsurface flow by soil erosion control practices. The higher volume of water moving through the soil profile

extracts more nitrogen from the soil than under conditions without conservation practices. For these fields, the nutrient 

management component of a farmer’s conservation plan would need to be enhanced to reduce or eliminate the negative effects of 

soil erosion control practices on nitrogen loss. 

To ensure that proper consideration is given to the effects of conservation practices on all of the resource concerns, USDA/NRCS 

developed a comprehensive planning tool referred to as CPPE (Conservation Practice Physical Effects). The CPPE is included in the 

Field Office Technical Guide. Conservation planners are expected to use CPPE as a reference to ensure that all resource concerns are 

addressed in conservation plans. 
Draft June 2010 Page 69 

Figure 35. Estimates of average annual total nitrogen loss for land in long-term conserving cover in the Upper Mississippi River 

Basin 

Figure 36. Estimates of average annual reduction in total nitrogen loss due to conversion to long-term conserving cover in the Upper 

Mississippi River Basin 

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Draft June 2010 Page 70 

Figure 37. Estimates of average annual nitrogen lost with surface runoff for cropped acres in the Upper Mississippi River Basin 

Figure 38. Estimates of average annual reduction in nitrogen lost with surface runoff due to the use of conservation practices on 

cropped acres in the Upper Mississippi River Basin 

Note: About 3 percent of the acres have negative reductions (net gain) in nitrogen lost with surface runoff due to conservation practices, resulting from a small number 

of acres with negative reductions in surface water runoff (see figure 17). 

 

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Draft June 2010 Page 71 

Figure 39. Estimates of average annual nitrogen loss in subsurface flow for cropped acres in the Upper Mississippi River Basin 

Figure 40. Estimates of average annual reduction in nitrogen loss in subsurface flow due to the use of conservation practices on 

cropped acres in the Upper Mississippi River Basin 

Note: See text for discussion of negative reductions. 

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Draft June 2010 Page 72 

Phosphorus Loss 

Phosphorus, like nitrogen, is an essential element needed for 

crop growth. Unlike nitrogen, however, phosphorus rarely 

occurs in a gaseous form so the agricultural model has no 

atmospheric component. Only phosphorus compounds that are 

soluble in water are available for plants to use. Although total 

phosphorus is plentiful in the soil, only a small fraction is 

available at any one time for plant uptake. Farmers apply 

commercial phosphate fertilizers to supplement low quantities 

of plant-available phosphorus in the soil. 

In the model simulations for the UMRB, about 22 pounds per 

acre of phosphorus were applied as commercial fertilizer or in 

manure to cropped acres, on average, in each year of the 

model simulation (table 19). The majority of the phosphorus 

applied is taken up by the crop and removed at harvest—17 

pounds per acre per year, on average. 

Total phosphorus loss for all loss pathways other than harvest 

averaged 3.0 pounds per acre per year in the baseline 

conservation condition (table 19). These phosphorus loss 

pathways are— 

 phosphorus lost with windborne sediment (average of 0.4 

pound per acre per year); 

 phosphorus lost with waterborne sediment (average of 1.6 

pounds per acre per year); 

 soluble phosphorus loss in surface runoff, including 

soluble phosphorus that infiltrates into the soil profile but 

quickly returns to surface water either through quick 

return lateral flow or intercepted by drainage systems 

(average of 1.0 pounds per acre per year); and 

 soluble phosphorus that percolates through the soil profile 

into the groundwater (average of 0.02 pound per acre per 

year). 

The percent of phosphorus lost in each loss pathway varies 

from acre to acre, as shown in figure 41 for cropped acres. The 

dominant loss pathway for most cropped acres—57 percent of 

the acres in the UMRB—is phosphorus lost with waterborne 

sediment. Soluble phosphorus loss in surface water runoff and 

lateral flow (including discharge to drainage ditches) was the 

dominant loss pathway for 32 percent of the acres. On average 

for all acres in the region, 85 percent of the phosphorus lost 

from fields is lost with surface runoff (sediment attached and 

soluble). Phosphorus loss with windborne sediment is the 

dominant loss pathway for 18 percent of the acres, 

representing 14 percent of total phosphorus loss from fields. 

Phosphorus loss in percolate is typically small, but is 

significant for a few acres, as shown in figure 41. 

As shown for nitrogen, total phosphorus losses are higher for 

acres receiving manure than for acres that did not receive 

manure (table 19). Phosphorus losses are only slightly higher 

for highly erodible land than for non-highly erodible land. 

Model simulations for the baseline conservation condition 

indicate that some cropped acres in the UMRB lose much 

higher amounts of phosphorus than other acres (figure 42). 

About half of the acres lose less than 3 pounds per acre per 

year through the various loss pathways other than removal at 

harvest under all weather conditions. About one-fourth of the 

acres, on the other hand, lose more than 6 pounds per acre in 

at least some years. 

Conservation practices have reduced total phosphorus loss for 

cropped acres by 49 percent, reducing the average loss from 

5.9 pounds per acre per year if conservation practices were not 

in use to 3.0 pounds per acre per year for the baseline 

conservation condition (table 19). 

The effects of conservation practices on phosphorus lost with 

surface runoff (soluble and sediment attached) are shown in 

figures 43 and 44 for cropped acres. Conservation practice use 

has reduced phosphorus lost with surface runoff by 48 percent 

on average, (table 19). With the conservation practices in use 

as represented by the baseline conservation condition, about 

15 percent of cropped acres exceed 4 pounds per acre per year. 

Without those practices in use, phosphorus lost with surface 

runoff would exceed 4 pounds per acre for 44 percent of the 

acres. Reductions in phosphorus lost with surface runoff due 

to conservation practice use in the baseline conservation 

condition vary throughout the UMRB as shown in figure 44. 

For land in long-term conserving cover, total phosphorus loss 

is 97 percent less than it would have been if crops had been 

grown, reducing total phosphorus loss by 7.4 pounds per acre 

per year on average (table 19, figures 45 and 46). 
Draft June 2010 Page 73 

Figure 41. Cumulative distributions of the proportion of phosphorus lost through various loss pathways

 

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Waterborne sediment Surface water runoff (soluble)

Percolation Windborne sediment
Draft June 2010 Page 74 

Table 19. Field-level effects of conservation practices on phosphorus sources and phosphorus loss pathways for cropped acres in the 

Upper Mississippi River Basin 

 Average annual values in pounds per acre 

Model simulated outcome 

Baseline 

conservation 

condition 

Nopractice 

scenario 

Reduction 

due to 

practices 

Percent 

reduction 

Cropped acres (58.2 million acres) 

Phosphorus sources 

 Phosphorus applied as commercial fertilizer and manure 22.31 29.53 7.22 24 

Phosphorus loss pathways 

Phosphorus in crop yield removed at harvest 16.98 17.82 0.84 5 

Phosphorus lost with windborne sediment 0.42 0.91 0.50 55 

Phosphorus lost with surface runoff, including waterborne 

sediment and soluble phosphorus in surface water runoff and 

lateral flow into drainage ditches 2.54 4.93 2.39 48 

Soluble phosphorus loss to groundwater 0.02 0.02 <0.01 15 

Total phosphorus loss for all pathways except harvest 2.98 5.87 2.89 49 

Change in soil phosphorus 2.24 5.79 3.56 -- 

Highly erodible land (18 percent of cropped acres) 

Phosphorus applied as commercial fertilizer and manure 23.12 29.04 5.92 20 

Total phosphorus loss for all pathways except harvest 4.64 9.29 4.64 50 

Non-highly erodible land (82 percent of cropped acres) 

Phosphorus applied as commercial fertilizer and manure 22.13 29.64 7.51 25 

Total phosphorus loss for all pathways except harvest 2.60 5.10 2.50 49 

Acres with manure applied (16 percent of cropped acres) 

Phosphorus applied as commercial fertilizer and manure 37.12 44.20 7.08 16 

Total phosphorus loss for all pathways except harvest 6.15 9.97 3.82 38 

Acres without manure applied (84 percent of cropped acres) 

Phosphorus applied as commercial fertilizer and manure 19.43 26.68 7.25 27 

Total phosphorus loss for all pathways except harvest 2.36 5.07 2.71 53 

 

Land in long-term conserving cover (2.8 million acres) 

Phosphorus sources 

 Phosphorus applied as commercial fertilizer and manure 0.00 29.87 29.87 100 

Phosphorus loss pathways 

Phosphorus in crop yield removed at harvest 0.48* 16.55 16.07 97 

Phosphorus lost with windborne sediment 0.00 0.11 0.11 100 

Phosphorus lost with surface runoff, including waterborne 

sediment and soluble phosphorus in surface water runoff and 

lateral flow into drainage ditches 0.19 7.52 7.33 97 

Soluble phosphorus loss to groundwater 0.07 0.03 -0.04 -137 

Total phosphorus loss for all pathways except harvest 0.26 7.66 7.40 97 

Change in soil phosphorus -0.86 5.47 6.33 -- 

* Harvest was simulated on acres planted to trees where expected tree age is less than the 47-years included in the model simulation. At tree harvest time, the grass also 

is removed and replanted.

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 C for the 14 subbasins. 
Draft June 2010 Page 75 

Figure 42. Distribution of annual total phosphorus loss for each year of the 47-year model simulation, Upper Mississippi River Basin 

Note: This figure shows how annual total phosphorus loss (pounds per acre per year) varied within the region and from year to year in the model simulation on cropped 

acres. Each of the 47 curves shown above represents a single year of data and shows how annual total phosphorus loss varied over the region in that year, starting with 

the acres with the lowest total phosphorus loss and increasing to the acres with the highest total phosphorus loss. The family of curves shows how annual total 

phosphorus loss varied from year to year. 

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Draft June 2010 Page 76 

Figure 43. Estimates of average annual phosphorus lost with surface runoff for cropped acres in the Upper Mississippi River Basin 

Figure 44. Estimates of average annual reduction in phosphorus lost with surface runoff due to conservation practices on cropped 

acres in the Upper Mississippi River Basin 

Note: A small number of acres with an overall increase in surface water runoff due to conservation practices (see figure 17) causes small negative reductions (gains) in 

phosphorus lost with surface runoff due to conservation practices for about 2 percent of the cropped acres. 

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Draft June 2010 Page 77 

Figure 45. Estimates of average annual total phosphorus loss for land in long-term conserving cover in the Upper Mississippi River 

Basin 

Figure 46. Estimates of average annual reduction in total phosphorus loss due to conversion to long-term conserving cover in the 

Upper Mississippi River Basin 

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Draft June 2010 Page 78 

Pesticide Residues and Environmental Risk 

Pesticide loss 

Use of pesticides to protect crops from weeds, insects, and 

diseases is an integral part of crop production. While 

pesticides are essential for large-scale agriculture, pesticide 

residues can migrate from the application site and lead to 

unintentional risk to humans and non-target plants and 

animals. Most pesticides are applied at much lower rates than 

nutrients. The fraction of pesticides applied that migrates 

offsite with water is generally less than 1 to 2 percent. 

Nevertheless, small amounts of pesticide residue can create 

water quality concerns depending on the toxicity of the 

pesticide residues to non-target species and even exceed EPA 

drinking water standards at times. 

The APEX model tracks the mass loss of pesticides dissolved 

in surface water runoff, adsorbed to sediment loss from water 

erosion, and dissolved in subsurface flow pathways.22 For the 

UMRB, the predominant loss pathway was pesticide loss in 

surface water runoff—50 percent of the total mass loss for the 

baseline conservation condition. About 29 percent of the total 

mass loss was with water-borne sediment. Pesticide loss in 

subsurface flow pathways averaged 21 percent of the total 

mass loss. 

The average annual amount of pesticide lost from farm fields 

in the UMRB is about 8.4 grams of active ingredient per 

hectare per year (table 20). As was observed for sediment and 

nutrient loss, the majority of pesticide loss occurs on a 

minority of acres within the UMRB. Two-thirds of the acres 

have total mass loss less than 8.4 grams of active ingredient 

per hectare per year, on average. In contrast, about 11 percent 

of the acres have an annual average pesticide mass loss of 

more than 20 grams of active ingredient per hectare. 

The pesticide applied in the largest amount was glyphosate, 

consisting of 28 percent of the total amount of pesticides 

applied in the UMRB (table 21). Atrazine was the second 

highest (23 percent), followed by acetochlor (18 percent) and 

s-metolachlor (9 percent). These 4 pesticides accounted for 78 

percent of the quantity of pesticides applied in the region. 

The most common pesticide residue lost from farm fields is 

atrazine, which represented about 37 percent of the total mass 

loss in these model simulations (table 21). Acetechlor 

represented 16 percent of the total pesticide mass loss and 

glyphosate represented 11 percent. 

Pesticide loss for land in long-term conserving cover was not 

simulated because the survey did not provide information on 

pesticide use on land enrolled in CRP General Signups. It was 

thus assumed that there was no pesticide residues lost from 

land in long-term conserving cover. 

 

22 The APEX model currently does not estimate pesticides lost in spray drift or 

volatilization. 

Environmental risk 

Management practices that reduce the impact of pesticides on 

non-target plant and animal populations consist of a 

combination of Integrated Pesticide Management (IPM) 

techniques and water erosion control practices. Water erosion 

control practices mitigate the loss of pesticides from farm 

fields by reducing surface water runoff and sediment loss, 

both of which carry pesticide residues from the farm field to 

the surrounding environment. IPM is site-specific in nature, 

with individual tactics determined by the particular 

crop/pest/environmental condition. IPM consists of a 

management strategy for prevention, avoidance, monitoring, 

and suppression of pest populations. When the use of 

pesticides is necessary to protect crop yields, selection of 

pesticides that have the least environmental risk is an 

important aspect of the suppression component of IPM. 

Model simulations show that conservation practices—

primarily water erosion control practices—are effective in 

reducing the loss of pesticide residues from farm fields. Use of 

conservation practices has reduced the loss of pesticides 

(summed over all pesticides) by an average of 8.4 grams of 

active ingredient per hectare per year, a 50-percent reduction 

from the 16.8 grams per hectare for the no-practice scenario 

(table 20). 

Because the environmental impact is specific to the toxicity of 

each pesticide to non-target species, however, the total 

quantity of all pesticides lost from the field is not the most 

useful outcome measure for assessing the environmental 

benefits of conservation practices. Pesticide risk indicators 

were developed to represent risk at the edge-of-the field 

(bottom of root zone for groundwater) to provide a consistent 

measure that would be comparable from field to field and that 

best represented the effects of farming activities without being 

influenced by other landscape factors. 

Risk indicators are based on the ratio of pesticide 

concentration to safe concentrations (toxicity thresholds) for 

each pesticide. As such, they do not have units. Risk indicator 

values of less than 1 are considered “safe” because the 

concentration is below the toxicity threshold for exposure at 

the edge-of-the field. The pesticide risk indicators were 

developed so that the relative risk for individual pesticides 

could be aggregated over the more than 150 pesticides in use 

on cropped acres in the UMRB. 23 

These indicators represent worst-case risk by assuming target 

species are exposed to concentrations at the edge of the field 

(bottom of root zone for groundwater). In most environmental 

 

23 A threshold value of 1 for the pesticide risk indicator applies when 

assessing the risk for a single pesticide. Since the indicator is summed over all 

pesticides in this study, a threshold value of 1 would still apply if pesticide 

toxicities are additive and no synergistic or antagonistic effects are produced 

when target species are exposed to a mix of pesticides. For more information 

on the derivation of the pesticide risk indicators, see “Documentation of 

pesticide risk indicators used in the CEAP cropland modeling,” found at 

http://www.nrcs.usda.gov/technical/nri/ceap/umrbdocumentation/. 
Draft June 2010 Page 79 

settings, however, target species are exposed to concentrations 

that have been diluted by water from other sources, even when 

those environments are located adjacent to a field. 

Consequently, these edge-of-field risk indicators cannot be 

used to predict actual environmental impacts. 

Three edge-of-field risk indicators are used here to assess the 

effects of conservation practices: (1) surface water pesticide 

risk indicator for aquatic ecosystems, (2) surface water 

pesticide risk indicator for humans, and (3) groundwater 

pesticide risk indicator for humans. The surface water risk 

indicator includes pesticide residues in solution in surface 

water runoff and in all subsurface water flow pathways that 

eventually return to surface water (water flow in a surface or 

tile drainage system, lateral subsurface water flow, and 

groundwater return flow). The pesticide risk indicator for 

aquatic ecosystems was based on pesticide toxicities for fish, 

invertebrates, algae, and vascular aquatic plants. The pesticide 

risk indicators for humans were based on drinking water 

standards or the equivalent for pesticides where standards 

have not been set. 

Atrazine was the dominant pesticide contributing to all three 

risk indicators (table 21). Based on the model simulations, the 

edge-of-field risk indicator for atrazine exceeded 1 for 28 

percent of the cropped acres for risk to aquatic ecosystems, 8 

percent of the cropped acres for surface water risk to humans, 

and 3 percent of the cropped acres for groundwater risk to 

humans. Atrazine's dominance in the risk indicators is due to 

its widespread use, its mobility (solubility = 30 mg/L; 

Koc = 100 g/ml), its persistence (field half life = 60 days), 

its toxicity to aquatic ecosystems (aquatic plant toxicity = 1 

ppb), and the human drinking water standard (EPA Maximum 

Contaminant Level = 3 ppb). 

The pesticide risk indicator for aquatic ecosystems averaged 

2.6 over all years and cropped acres (table 20) for the baseline 

conservation condition. (The 2.6 value indicates that pesticide 

concentrations in water leaving cropped fields in the UMRB 

are, on average, 2.6 times the “safe” concentration for nontarget plant and animal species.) Figure 47 shows that for most 

years the overall risk for aquatic ecosystems is low for the 

majority of acres, in part because of the conservation practices 

in use, but in some years the edge-of-field concentrations can 

be high relative to "safe" thresholds for some of the acres. 

The pesticide risk indicators for humans were much lower, 

averaging 0.4 for surface water and 0.1 for groundwater. 

The use of conservation practices in the UMRB has reduced 

the surface water pesticide risk indicators by 48 to 51 percent 

(table 20), averaged over all years, all pesticides, and all 

cropped acres in the UMRB. The groundwater pesticide risk 

indicator has been reduced by 30 percent, on average. 

The distributions of the surface water pesticide risk indicators 

are shown in figures 48 and 49. For environmental risk to 

aquatic ecosystems, 40 percent of the acres have an annual 

average indicator greater than 1 in the baseline conservation 

condition, compared to 55 percent of the acres without 

conservation practices. The annual average surface water risk 

indicator for humans is greater than 1 for 11 percent of the 

acres in the baseline conservation condition, compared to 21 

percent of the acres without conservation practices. 

Figure 50 shows the distribution of the reductions in the two 

pesticide risk indicators due to conservation practices. The 

benefits of conservation practices were similar for both 

aquatic risks and human risks on the acres that had those risks, 

but aquatic risks were more widespread than human risks so 

conservation practices have greater total benefit for aquatic 

ecosystems than for human drinking water. 

 
Draft June 2010 Page 80 

Table 20. Field-level effects of conservation practices on pesticide loss and associated edge-of-field environmental risk for cropped 

acres in the Upper Mississippi River Basin 

Model simulated outcome 

Baseline 

conservation 

condition 

No-practice 

scenario 

Reduction 

due to 

practices 

Percent 

reduction 

Pesticide sources 

Average annual amount of pesticides applied (grams of 

active ingredient/hectare) 1,650 2,079 429 21 

Pesticide loss 

Average annual mass loss of pesticides for all pathways 

(grams of active ingredient/hectare) 8.4 16.8 8.4 50 

Edge-of-field pesticide risk indicator 

Average annual surface water pesticide risk indicator for 

aquatic ecosystem 2.6 5.3 2.7 51 

Average annual surface water pesticide risk indicator for 

humans 0.4 0.8 0.4 48 

Average annual groundwater pesticide risk indicator for 

humans 0.2 0.2 0.1 30 

Note: It was assumed that no pesticides were applied to land in long-term conserving cover and there was no data on residual pesticides in the soil for these acres; thus, 

the assessment of the effects of this practice on pesticide loss was not done. 

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 C for the 14 subbasins.

 
Draft June 2010 Page 81 

Table 21. Dominant pesticides applied, contributing to losses, and in determining edge-of-field environmental risk, Upper Mississippi 

River Basin 

Pesticide (active ingredient name) Pesticide type Percent of total applied in the UMRB 

Pesticide application* 

Glyphosate, isopropylamine sal Herbicide 28 

Atrazine Herbicide 23 

Acetochlor Herbicide 18 

S-Metolachlor Herbicide 9 

Metolachlor Herbicide 2 

Pendimethalin Herbicide 2 

Dimethenamide-P Herbicide 2 

Chlorpyrifos Insecticide 2 

Trifluralin Herbicide 1 

Dimethenamid Herbicide 1 

Total 87 

 

 Percent of total pesticide loss in the UMRB** 

Pesticide loss from farm fields* 

Atrazine Herbicide 37 

Glyphosate, isopropylamine salt Herbicide 16 

Acetochlor Herbicide 11 

S-Metolachlor Herbicide 8 

Sulfentrazone Herbicide 8 

Metolachlor Herbicide 3 

Pendimethalin Herbicide 2 

Flufenacet Herbicide 1 

Dimethenamide-P Herbicide 1 

Clopyralid Herbicide 1 

Simazine Herbicide 1 

Total 88 

 Percent of cropped acres with 

average annual edge-of-field risk indicator 

greater than 1 

Risk indicator for aquatic ecosystem 

Atrazine Herbicide 28 

Acetochlor Herbicide 6 

Phostebupirim Insecticide 4 

Metolachlor Herbicide 2 

Chlorpyrifos Insecticide 2 

Tefluthrin Insecticide <1 

Carbofuran Insecticide <1 

S-Metolachlor Herbicide <1 

Flufenaret Herbicide <1 

All others combined <2 

 

Risk indicator for humans, surface water 

Atrazine Herbicide 8 

Alachlor Herbicide <1 

Acetochlor Herbicide <1 

Simazine Herbicide <1 

All others combined <1 

 

Risk indicator for humans, groundwater 

Atrazine Herbicide 3 

All others combined <1 

* Pesticides not listed each represented less than 1 percent of the total. 

** Includes loss of pesticides dissolved in surface water runoff, adsorbed to sediment loss from water erosion, and dissolved in subsurface flow pathways.

 
Draft June 2010 Page 82 

Figure 47. Distribution of annual values of the edge-of-field pesticide risk indicator for aquatic ecosystems for each year of the 47-

year model simulation, Upper Mississippi River Basin 

Note: This figure shows how the annual values of the risk indicator varied within the region and from year to year in the model simulation on cropped acres. Each of 

the 47 curves shown above represents a single year of data and shows how annual values of the risk indicator varied over the region in that year, starting with the acres 

with the lowest value and increasing to the acres with the highest value. The family of curves shows how annual values varied from year to year.

0

2

4

6

8

10

12

14

16

18

20

22

24

26

28

30

0 10 20 30 40 50 60 70 80 90 100

Annual pesticide risk indicator for aquatic ecosystem

Cumulative percent acres
Draft June 2010 Page 83 

Figure 48. Estimates of average annual edge-of-field surface water pesticide risk indicator for aquatic ecosystem in the Upper 

Mississippi River Basin 

Figure 49. Estimates of average annual edge-of-field surface water pesticide risk indicator for humans in the Upper Mississippi River 

Basin 

0

5

10

15

20

25

30

35

40

45

50

0 10 20 30 40 50 60 70 80 90 100

Average annual surface water pesticide risk 

indicator for the aquatic ecosystem

Cumulative percent acres

Baseline conservation condition No-practice scenario

0

1

2

3

4

5

6

7

8

9

10

0 10 20 30 40 50 60 70 80 90 100

Average annual surface water pesticide risk 

indicator for humans

Cumulative percent acres

Baseline conservation condition No-practice scenario
Draft June 2010 Page 84 

Figure 50. Estimates of average annual reductions in the surface water pesticide risk indicators for aquatic ecosystems in the Upper 

Mississippi River Basin 

Note: Negative reductions in pesticide risk indicators result primarily from an increase in surface water runoff due to conservation practices (see figure 17). 

-10

-8

-6

-4

-2

0

2

4

6

8

10

12

14

16

18

20

22

24

26

28

30

0 10 20 30 40 50 60 70 80 90 100

Average annual reduction in surface water pesticide 

risk indicators

Cumulative percent acres

Aquatic ecosystem Humans
Draft June 2010 Page 85 

Chapter 5 

Offsite Water Quality Effects of 

Conservation Practices 

The results from the onsite APEX model simulations for 

cultivated cropland, including land in long-term conserving 

cover, were integrated into HUMUS/SWAT to assess the 

effects of conservation practices on instream loads and 

concentrations of sediment, nitrogen, phosphorus, and atrazine 

in the UMRB. 

HUMUS/SWAT accounts for the transport of water, sediment, 

pesticides, 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 sediment, 

nutrients, and pesticides that leave farm fields are delivered to 

streams and rivers. Some material is bound up permanently in 

various parts of the landscape during transport. In addition, 

instream degradation processes and streambed deposition and 

accumulation remove or trap a portion of the sediment, 

nutrients, and pesticides delivered to streams and rivers. 

HUMUS/SWAT model simulations provide comparisons 

between the baseline conservation condition and the nopractice scenario. For each scenario, only the conditions for 

cultivated cropland were changed; all other aspects of the 

simulations—including sediment and nutrient loads from point 

sources and noncultivated land uses—remained the same. 

There are three types of loadings that are relevant to assessing 

the effects of conservation practices: 1) loadings leaving the 

field (summarized in the previous chapter), 2) loadings 

delivered to streams and rivers, and 3) loadings in the stream 

or river at a given point. Loadings delivered to streams and 

rivers differ from the amount leaving the field because of 

losses during transport from the field to the stream. Instream 

loadings are further influenced by loadings exported from 

upstream subbasins and losses during transport within the 

stream or river. 

Atrazine was the only pesticide for which in-stream loads 

were assessed in the UMRB because it was the dominant 

contributor to mass loss of pesticide residues from farm fields 

and the primary contributor to environmental risk from 

pesticides in the region. 

Summary of Results for the Entire Basin 

The assessment shows that conservation practices as 

represented in the baseline conservation condition have 

reduced the delivery of loads from cultivated cropland into 

rivers and streams by— 

 71 percent for sediment (table 22) ; 

 23 percent for nitrogen (table 24); 

 49 percent for phosphorus (table 26); and 

 49 percent for atrazine (table 28). 

These reductions in cultivated cropland source loads have in 

turn significantly reduced the amount of these agricultural 

pollutants found at the farthest downstream gauging station 

above the confluence with the Missouri River at Grafton, IL, 

where— 

 instream sediment loads have been reduced 37 percent 

due to conservation practices (table 23and figure 51); 

 instream nitrogen loads have been reduced 21 percent due 

to conservation practices (table 25 and figure 52); 

 instream phosphorus loads have been reduced 40 percent 

due to conservation practices (table 27 and figure 53); and 

 instream atrazine loads have been reduced 51 percent due 

to conservation practices (table 29 and figure 54). 

The model simulation also identifies the proportion of 

instream sediment and nutrient loads that originate from 

cultivated cropland. (Atrazine sources other than agriculture 

were not included in the model simulation.) At Grafton, IL, 

the most downstream point in the UMRB, the percentage of 

instream loads attributed to cultivated cropland sources for the 

baseline conservation condition is— 

 28 percent for sediment; 

 74 percent for nitrogen; and 

 65 percent for phosphorus. 

Summary of Results for the 14 Subbasins 

Delivery of loads from cultivated cropland 

The delivery of sediment, nutrients, and pesticides into rivers 

and streams from cultivated cropland varies among the 14 

subbasins within the UMRB (tables 22, 24, 26, and 28): 

 The Upper Mississippi-Iowa-Skunk-Wapsipinicon 

(subbasin code 0708), the Rock River (subbasin code 

0709), and the Lower Illinois River (subbasin code 0713) 

contribute the largest sediment loads from agricultural 

sources. More than 65 percent of the land cover is 

cultivated cropland in these three subbasins, among the 

highest in the UMRB (table 4). 

 Two subbasins contribute the largest nitrogen, 

phosphorus, and atrazine loads from agricultural 

sources—the Upper Mississippi-Iowa-SkunkWapsipinicon (subbasin code 0708) and the Lower 

Illinois River (subbasin code 0713). 

 The Rock River (subbasin code 0709) also contributes 

among the largest amounts of phosphorus loads in the 

basin. 

 Three subbasins contribute among the smallest sediment, 

nutrient, and atrazine loads from agricultural sources—the 

St. Croix River (subbasin code 0703), the Chippewa River 

(subbasin code 0705), and the Mississippi Headwaters 

(subbasin code 0701). These three subbasins also have the 
Draft June 2010 Page 86 

lowest percentage of land cover in cultivated cropland 

(less than 25 percent). 

The effects of conservation practices on reducing the loads 

delivered from cultivated cropland to rivers and streams also 

vary (tables 22, 24, 26, and 28): 

 Subbasins with the largest percent reductions in sediment 

delivered to rivers and streams due to conservation 

practices include the Upper Mississippi-Maquoketa-Plum 

(subbasin code 0706), the Des Moines River Basin 

(subbasin code 0710), the Upper Mississippi-Iowa-SkunkWapsipinicon (subbasin code 0708), and the Upper 

Mississippi-Salt (subbasin code 0711). Reductions in 

sediment delivered were 77 percent or higher in these four 

subbasins. 

 Three subbasins have reductions in nitrogen delivered to 

rivers and streams due to conservation practices of 37 

percent or more: 

o the Upper Mississippi-Maquoketa-Plum (subbasin 

code 0706), 

o the Des Moines River basin (subbasin code 0710), 

and 

o the Mississippi Headwaters (subbasin code 0701). 

 Subbasins with the largest percent reductions in 

phosphorus delivered to rivers and streams due to 

conservation practices include the Upper MississippiMaquoketa-Plum watershed (subbasin code 0706), the 

Upper Mississippi-Salt (subbasin code 0711), and the Des 

Moines River (subbasin code 0701). Reductions in 

phosphorus delivered were 55 percent or higher in these 

three subbasins. 

 The Minnesota River Basin (subbasin code 0711) has the 

highest percent reduction (65 percent) in atrazine 

delivered to streams and rivers. 

 The Upper Mississippi-Maquoketa-Plum watershed 

(subbasin code 0706) and the Upper Mississippi-Salt 

(subbasin code 0711) have among the highest percent 

reductions of sediment and nutrients delivered into 

streams and rivers due to conservation practices currently 

in use. These two subbasins also have the highest 

proportion of cultivated cropland acres in long-term 

conserving cover—more than 10 percent of the cultivated 

cropland in the subbasins. 

Instream loads 

Four of the 14 subbasins within the UMRB have outlets along 

the main stem of the Upper Mississippi River and receive 

loads from upstream sources in addition to loads from within 

the subbasin. They are: 

1. Upper Mississippi-Black-Root (subbasin code 0704) 

2. Upper Mississippi-Maquoketa-Plum (subbasin code 0706) 

3. Upper Mississippi-Iowa-Skunk-Wapsipinicon (subbasin 

code 0708) 

4. Upper Mississippi-Salt (subbasin code 0711) at Grafton, 

IL. 

Instream loads for these four subbasins consistently increase 

from the upstream to the downstream subbasins (tables 23, 25, 

27, and 29). Instream loads among the nine tributaries and the 

farthest upstream watershed on the main stem of the Upper 

Mississippi River—subbasin code 0701—can be directly 

compared as these are loads that are delivered into the Upper 

Mississippi River. 

Percent reductions in instream loads due to conservation 

practices were highly variable among tributary subbasins, but 

were much less variable among the five subbasins along the 

mainstem of the Upper Mississippi River. 

Agricultural sources are relatively minor in two subbasins, the 

St. Croix River (subbasin code 0703) and the Upper Illinois 

River (subbasin code 0712), which explains the low percent 

reduction in instream loads due to conservation practices in 

those subbasins. 

The effects of conservation practices on reducing instream 

loads for the mainstem subbasins are summarized graphically 

in figures 51 through 54.
Draft June 2010 Page 87 

Table 22. Average annual sediment source loads delivered from cultivated cropland for the 14 subbasins in the Upper Mississippi 

River Basin 

 Baseline 

conservation condition 

Reductions in loads due 

to conservation practices 

Subbasin 

code Subbasin name 

Amount 

(1,000 tons) 

Percent 

of basin 

total 

Tons 

delivered per 

cropland 

acre 

No-practice 

 Scenario 

(1,000 tons) 

Reduction 

(1,000 tons) Percent

0701 Mississippi Headwaters 775 4 0.25 1,400 623 45 

0702 Minnesota River Basin 996 5 0.12 2,640 1,650 62 

0703 St. Croix River Basin 301 1 0.48 659 358 54 

0704 Upper Mississippi-Black-Root 1,780 9 0.54 5,070 3,290 65 

0705 Chippewa River Basin 764 4 0.55 1,560 795 51 

0706 Upper Mississippi-MaquoketaPlum 1,340 7 0.45 6,100 4,770 78 

0707 Wisconsin River Basin 1,050 5 0.44 2,710 1,660 61 

0708 Upper Mississippi-Iowa-SkunkWapsipinicon 4,130 20 0.38 18,300 14,100 77 

0709 Rock River Basin 2,610 13 0.56 7,260 4,640 64 

0710 Des Moines River Basin 1,220 6 0.19 6,190 4,980 80 

0711 Upper Mississippi-Salt 1,360 7 0.46 5,850 4,490 77 

0712 Upper Illinois River Basin 1,050 5 0.26 3,050 2,000 66 

0713 Lower Illinois River Basin 2,340 11 0.29 8,170 5,830 71 

0714 Upper Mississippi-KaskaskiaMeramec 798 4 0.23 2,600 1,800 69 

 Total 20,500 100 0.33 71,600 51,000 71 

Note: Percent reductions were calculated prior to rounding the values for reporting in the table and the associated text. 

Table 23. Average annual instream sediment loads for the 14 subbasin outlets in the Upper Mississippi River Basin 

Baseline 

conservation condition 

 Reductions in loads 

due to conservation 

practices 

Subbasin 

code Location of subbasin outlet 

Load from 

all sources 

(1,000 tons) 

Background 

sources* 

(1,000 tons) 

Percent of load 

attributed to 

cultivated 

cropland sources 

Nopractice 

scenario 

(1,000 

tons) 

Reduction

(1,000 tons) Percent 

Tributary subbasins 

0702 Minnesota River 873 596 32 1,280 407 32 

0703 St. Croix River 520 500 4 538 18 3 

0705 Chippawa River 962 686 29 1,070 108 10 

0707 Wisconsin River 1,120 863 23 1,520 400 26 

0708a Iowa River within 708 1,630 937 43 2,970 1,340 45 

0709 Rock River 1,530 682 55 2,850 1,320 46 

0710 Des Moines River 792 524 34 1,240 448 36 

0713 Illinois River 6,380 4,600 28 9,410 3,030 32 

0712 Upper Illinois River within 713 1,960 1,680 14 2,460 500 20 

Outlets along main stem 

0701 Mississippi Headwaters 2,620 1,830 30 3,540 920 26 

0704 Upper Mississippi-Black-Root 5,980 4,100 31 7,990 2,010 25 

0706 Upper Mississippi-MaquoketaPlum 9,040 6,270 31 14,200 5,160 36 

0708 Upper Mississippi-Iowa-SkunkWapsipinicon 15,600 10,600 32 26,700 11,100 42 

0711 Mississippi at Grafton, Illinois 20,900 15,100 28 33,300 12,400 37 

* Loadings from non-cultivated cropland were estimated by running an additional scenario that simulated a grass cover without any tillage or addition of nutrients or 

pesticides for all cultivated cropland acres, labeled “Background sources.” 

Note: Percent reductions were calculated prior to rounding the values for reporting in the table and the associated text. 
Draft June 2010 Page 88 

Table 24. Average annual nitrogen source loads delivered from cultivated cropland for the 14 subbasins in the Upper Mississippi 

River Basin 

 Baseline 

conservation condition 

Reductions in loads due 

to conservation practices 

Subbasin 

code Subbasin name 

Amount 

(1,000 

pounds) 

Percent 

of basin 

total 

Pounds 

delivered per 

cropland 

acre 

No-practice 

 Scenario 

(1,000 

pounds) 

Reduction 

(1,000 pounds) Percent

0701 Mississippi Headwaters 34,900 3 11.3 58,300 23,500 40 

0702 Minnesota River Basin 117,000 11 14.1 151,000 34,700 23 

0703 St. Croix River Basin 11,200 1 17.8 16,800 5,620 33 

0704 Upper Mississippi-Black-Root 58,500 5 17.9 88,700 30,200 34 

0705 Chippewa River Basin 20,100 2 14.5 30,600 10,500 34 

0706 Upper Mississippi-MaquoketaPlum 51,500 5 17.2 82,000 30,600 37 

0707 Wisconsin River Basin 44,800 4 18.7 67,000 22,100 33 

0708 Upper Mississippi-Iowa-SkunkWapsipinicon 215,000 20 20.0 272,000 56,600 21 

0709 Rock River Basin 89,200 8 19.1 116,000 26,600 23 

0710 Des Moines River Basin 109,000 10 16.6 136,000 27,800 20 

0711 Upper Mississippi-Salt 32,800 3 11.1 53,000 20,200 38 

0712 Upper Illinois River Basin 99,000 9 24.4 120,000 21,200 18 

0713 Lower Illinois River Basin 170,000 16 21.1 183,000 13,000 7 

0714 Upper Mississippi-KaskaskiaMeramec 46,200 4 13.3 55,800 9,570 17 

 Total 1,100,000 100 17.6 1,430,000 332,000 23 

Note: Percent reductions were calculated prior to rounding the values for reporting in the table and the associated text. 

Note: Percents may not add to totals because of rounding. 

Table 25. Average annual instream nitrogen loads for the 14 subbasin outlets in the Upper Mississippi River Basin 

Baseline 

conservation condition 

 Reductions in loads 

due to conservation 

practices 

Subbasin 

code Location of subbasin outlet 

Load from 

all sources 

(1,000 

pounds) 

Background 

sources* 

(1,000 pounds) 

Percent of load 

attributed to 

cultivated 

cropland 

sources 

No-practice 

scenario 

(1,000 

pounds) 

Reduction

(1,000 

pounds) Percent 

Tributary subbasins 

0702 Minnesota River 108,000 8,980 92 139,000 31,000 22 

0703 St. Croix River 13,600 11,800 13 15,000 1,400 9 

0705 Chippawa River 23,500 10,600 55 29,200 5,700 19 

0707 Wisconsin River 43,400 16,600 62 59,300 15,900 27 

0708a Iowa River within 708 117,000 21,400 82 148,000 31,000 21 

0709 Rock River 94,200 26,900 71 116,000 21,800 19 

0710 Des Moines River 117,000 17,600 85 140,000 23,000 17 

0713 Illinois River 424,000 198,000 53 454,000 30,000 6 

0712 Upper Illinois River within 713 166,000 104,000 37 180,000 14,000 8 

Outlets along main stem 

0701 Mississippi Headwaters 185,000 37,500 80 241,000 56,000 24 

0704 Upper Mississippi-Black-Root 304,000 79,000 74 401,000 97,000 24 

0706 Upper Mississippi-MaquoketaPlum 409,000 109,000 73 551,000 142,000 26 

0708 Upper Mississippi-Iowa-SkunkWapsipinicon 764,000 181,000 76 995,000 231,000 23 

0711 Mississippi at Grafton, Illinois 1,090,000 281,000 74 1,380,000 290,000 21 

* Loadings from non-cultivated cropland were estimated by running an additional scenario that simulated a grass cover without any tillage or addition of nutrients or 

pesticides for all cultivated cropland acres, labeled “Background sources”. 

Note: Percent reductions were calculated prior to rounding the values for reporting in the table and the associated text. 

 
Draft June 2010 Page 89 

Table 26. Average annual phosphorus source loads delivered from cultivated cropland for the 14 subbasins in the Upper 

Mississippi River Basin 

 Baseline 

conservation condition 

Reductions in loads due to 

conservation practices 

Subbasin 

code Subbasin name 

Amount 

(1,000 

pounds) 

Percent 

of basin 

total 

Pounds 

delivered per 

cropland 

acre 

No-practice 

 Scenario 

(1,000 

pounds) 

Reduction 

(1,000 pounds) Percent

0701 Mississippi Headwaters 2,490 4 0.8 4,970 2,480 50 

0702 Minnesota River Basin 3,930 6 0.5 8,460 4,530 54 

0703 St. Croix River Basin 757 1 1.2 1,400 640 46 

0704 Upper Mississippi-Black-Root 3,810 6 1.2 7,690 3,880 50 

0705 Chippewa River Basin 1,910 3 1.4 3,020 1,110 37 

0706 Upper Mississippi-MaquoketaPlum 3,060 5 1.0 7,220 4,160 58 

0707 Wisconsin River Basin 5,870 9 2.5 9,040 3,170 35 

0708 Upper Mississippi-Iowa-SkunkWapsipinicon 10,800 17 1.0 22,500 11,800 52 

0709 Rock River Basin 6,740 11 1.4 12,100 5,370 44 

0710 Des Moines River Basin 3,960 6 0.6 9,820 5,860 60 

0711 Upper Mississippi-Salt 3,260 5 1.1 7,290 4,030 55 

0712 Upper Illinois River Basin 3,500 6 0.9 6,940 3,440 50 

0713 Lower Illinois River Basin 8,690 14 1.1 15,500 6,790 44 

0714 Upper Mississippi-KaskaskiaMeramec 3,500 6 1.0 6,250 2,750 44 

 Total 62,300 100 1.0 122,000 60,000 49 

Note: Percent reductions were calculated prior to rounding the values for reporting in the table and the associated text. 

Note: Percents may not add to totals because of rounding. 

 

Table 27. Average annual instream phosphorus loads for the 14 subbasin outlets in the Upper Mississippi River Basin 

Baseline 

conservation condition Nopractice 

scenario 

(1,000 

pounds) 

Reductions in loads 

due to conservation 

practices 

Subbasin 

code Location of subbasin outlet 

Load from 

all sources 

(1,000 

pounds) 

Background 

sources* 

 (1,000 

pounds) 

Percent of load 

attributed to 

cultivated 

cropland sources 

Reduction

(1,000 

pounds) Percent 

Tributary subbasins 

0702 Minnesota River 3,340 975 71 6,530 3,190 49 

0703 St. Croix River 521 428 18 647 126 19 

0705 Chippawa River 1,610 530 67 2,230 620 28 

0707 Wisconsin River 2,830 799 72 4,440 1,610 36 

0708a Iowa River within 708 6,000 1,470 76 10,700 4,700 44 

0709 Rock River 6,060 1,430 76 9,900 3,840 39 

0710 Des Moines River 3,540 999 72 7,340 3,800 52 

0713 Illinois River 24,100 15,500 36 31,700 7,600 24 

0712 Upper Illinois River within 713 10,800 9,170 15 12,700 1,900 15 

Outlets along main stem 

0701 Mississippi Headwaters 7,250 2,930 60 13,100 5,850 44 

0704 Upper Mississippi-Black-Root 12,700 4,710 63 21,800 9,100 42 

0706 Upper Mississippi-MaquoketaPlum 19,000 5,830 69 31,800 12,800 40 

0708 Upper Mississippi-Iowa-SkunkWapsipinicon 35,200 10,200 71 59,600 24,400 41 

0711 Mississippi at Grafton, Illinois 45,200 15,800 65 74,900 29,700 40 

* Loadings from non-cultivated cropland were estimated by running an additional scenario that simulated a grass cover without any tillage or addition of nutrients or 

pesticides for all cultivated cropland acres, labeled “Background sources”. 

Note: Percent reductions were calculated prior to rounding the values for reporting in the table and the associated text. 
Draft June 2010 Page 90 

Table 28. Average annual atrazine source loads delivered from cultivated cropland for 14 subbasins in the Upper Mississippi River 

Basin 

 Baseline 

conservation condition 

Reductions in loads due 

to conservation practices 

Subbasin 

code Subbasin name 

Amount 

(pounds) 

Percent 

of basin 

total 

Pounds 

delivered per 

cropland 

acre 

No-practice 

 Scenario 

(pounds) 

Reduction 

(pounds) Percent

0701 Mississippi Headwaters 2,554 2 0.0008 3,397 843 25 

0702 Minnesota River Basin 3,741 3 0.0005 10,669 6,929 65 

0703 St. Croix River Basin 553 0.4 0.0009 845 292 35 

0704 Upper Mississippi-Black-Root 2,691 2 0.0008 5,391 2,700 50 

0705 Chippewa River Basin 1,979 2 0.0014 3,088 1,109 36 

0706 Upper Mississippi-MaquoketaPlum 5,240 4 0.0017 10,173 4,933 48 

0707 Wisconsin River Basin 2,129 2 0.0009 3,516 1,387 39 

0708 Upper Mississippi-Iowa-SkunkWapsipinicon 27,749 22 0.0026 58,753 31,003 53 

0709 Rock River Basin 7,876 6 0.0017 16,277 8,401 52 

0710 Des Moines River Basin 9,582 7 0.0015 20,436 10,854 53 

0711 Upper Mississippi-Salt 12,138 9 0.0041 22,068 9,930 45 

0712 Upper Illinois River Basin 11,252 9 0.0028 19,025 7,773 41 

0713 Lower Illinois River Basin 29,392 23 0.0036 57,909 28,517 49 

0714 Upper Mississippi-KaskaskiaMeramec 11,713 9 0.0034 17,802 6,089 34 

 Total 129,000 100 0.0021 249,000 120,000 49 

Note: Percent reductions were calculated prior to rounding the values for reporting in the table and the associated text. 

Note: Percents may not add to totals because of rounding. 

Table 29. Average annual instream atrazine loads for the 14 subbasin outlets in the Upper Mississippi River Basin 

 Reductions in loads due to 

conservation practices 

Subbasin 

code Location of subbasin outlet 

Baseline 

conservation 

condition 

(pounds) 

No-practice 

scenario 

(pounds) 

Reduction

(pounds) Percent 

Tributary subbasins 

0702 Minnesota River 3,052 8,885 5,833 66 

0703 St. Croix River 128 201 73 36 

0705 Chippawa River 854 1,217 363 30 

0707 Wisconsin River 1,146 1,540 393 26 

0708a Iowa River within 708 9,614 19,245 9,631 50 

0709 Rock River 4,915 10,219 5,304 52 

0710 Des Moines River 3,800 7,428 3,629 49 

0713 Illinois River 17,297 33,163 15,866 48 

0712 Upper Illinois River within 713 7,144 11,538 4,393 38 

Outlets along main stem 

0701 Mississippi Headwaters 5,470 12,355 6,885 56 

0704 Upper Mississippi-Black-Root 7,901 16,477 8,576 52 

0706 Upper Mississippi-MaquoketaPlum 6,315 11,861 5,546 47 

0708 Upper Mississippi-Iowa-SkunkWapsipinicon 33,335 69,607 36,272 52 

0711 Mississippi at Grafton, Illinois 47,826 98,025 50,199 51 

Note: Atrazine sources other than agriculture were not included in the model simulation. 

Note: Percent reductions were calculated prior to rounding the values for reporting in the table and the associated text. 

 
Draft June 2010 Page 91 

Figure 51. Estimates of average annual instream sediment loads for the baseline conservation condition compared to the no-practice 

scenario for subbasins in the Upper Mississippi River Basin 

Note: Loadings from all sources other than cultivated cropland are labeled “background” in the figure; for this scenario, cultivated cropland was simulated using a 

continuous grass cover without any tillage or addition of nutrients or pesticides and no harvest.
Draft June 2010 Page 92 

Figure 52. Estimates of average annual instream nitrogen loads for the baseline conservation condition compared to the no-practice 

scenario for subbasins in the Upper Mississippi River Basin 

Note: Loadings from all sources other than cultivated cropland are labeled “background” in the figure; for this scenario, cultivated cropland was simulated using a 

continuous grass cover without any tillage or addition of nutrients or pesticides and no harvest.
Draft June 2010 Page 93 

Figure 53. Estimates of average annual instream phosphorus loads for the baseline conservation condition compared to the no-practice 

scenario for subbasins in the Upper Mississippi River Basin 

Note: Loadings from all sources other than cultivated cropland are labeled “background” in the figure; for this scenario, cultivated cropland was simulated using a 

continuous grass cover without any tillage or addition of nutrients or pesticides and no harvest.
Draft June 2010 Page 94 

Figure 54. Estimates of average annual instream atrazine loads for the baseline conservation condition compared to the no-practice 

scenario for subbasins in the Upper Mississippi River Basin 

 
Draft June 2010 Page 95 

Chapter 6 

Assessment of Conservation 

Treatment Needs 

The adequacy of the conservation practices in use in the 

UMRB was evaluated to identify remaining conservation 

treatment needs for controlling sediment and nutrient loss. 

Field-level results for the baseline conservation conditions 

were used to make the assessment. Adequate conservation 

treatment consists of combinations of conservation practices 

that treat the specific inherent vulnerability factors associated 

with each field. Four resource concerns were evaluated: 

1. Sediment loss due to water erosion 

2. Nitrogen lost with surface runoff (nitrogen attached to 

sediment and in solution) 

3. Nitrogen loss in subsurface flow 

4. Phosphorus lost with surface runoff (phosphorus attached 

to sediment and in solution) 

The assessment showed that the suite of practices in use in the 

UMRB was often inadequate to address all four resource 

concerns simultaneously. 

The conservation treatment needs for controlling pesticide loss 

were not evaluated because it requires information on pest 

infestations, which was not available for the CEAP sample 

points. A portion of the pesticide residues are controlled by 

soil erosion control practices; meeting soil erosion control 

treatment needs would provide partial protection against loss 

of pesticide residues from farm fields. Integrated Pest 

Management (IPM) practices are also effective in reducing the 

risk associated with pesticide residues leaving the farm field. 

Determination of adequate IPM, however, is highly dependent 

on the specific site conditions and the nature and extent of the 

pest problems. 

Conservation Treatment Levels 

Four levels of conservation treatment (high, moderately high, 

moderate, and low) were defined as combinations of 

conservation practices for controlling (1) sediment loss due to 

water erosion, (2) nitrogen lost with surface runoff, and (3) 

phosphorus lost with surface runoff. Criteria for these 

management levels are presented in figures 55, 56, and 57, 

along with results on the extent to which these management 

levels are represented in the UMRB. The nitrogen 

management level presented in figure 11 was used to evaluate 

the adequacy of conservation treatment for nitrogen loss in 

subsurface flow. 

A “high” level of treatment was shown by model simulations 

to reduce sediment and nutrient losses to acceptable levels for 

nearly all cropped acres in the UMRB. Key findings are: 

 A high level of water erosion control treatment 

(combination of structural practices and residue and 

tillage management practices) is in use on about 40 

percent of cropped acres (figure 55). However, only about 

16 percent of the highly erodible acres have this level of 

treatment. About 35 percent of the highly erodible acres 

have a moderately high level of water erosion control 

treatment. 

 A high level of treatment for nitrogen runoff (combination 

of structural practices, residue and tillage management 

practices, and nitrogen management practices) is in use on 

only 3 percent of the acres (figure 56). About 41 percent 

of the acres have combinations of practices that indicate a 

moderately high level of treatment. 

 A high level of treatment for phosphorus runoff is in use 

on 10 percent of the acres (figure 57). About 37 percent of 

the acres have a moderately high level of treatment for 

controlling phosphorus loss with surface runoff. 

Inherent Vulnerability Factors 

Not all acres require the same level of conservation treatment 

because of differences in inherent vulnerabilities. Inherent 

vulnerability factors for surface runoff include soil properties 

that promote surface water runoff and erosion. Inherent 

vulnerability factors for loss of nutrients in subsurface flow 

include soil properties that promote infiltration. 

Soil runoff and leaching potentials were estimated for each 

sample point on the basis of vulnerability criteria presented in 

figures 58 and 59. A single set of criteria were developed for 

all regions and soils in the US to allow for regional 

comparisons. The spatial distribution of the soil runoff and 

leaching potentials within the UMRB are presented in figures 

60 and 61. The maps show the soil potentials for all soils and 

land uses in the region. For the assessment of conservation 

treatment needs, however, only the soil potentials for cropped 

acres were used. 

The majority of cropped acres in the UMRB have a low or 

moderate soil runoff potential (figure 58). About 13 percent of 

the acres have a high soil runoff potential, consisting almost 

entirely of highly erodible land. 

About 69 percent of the cropped acres have a moderate soil 

leaching potential (figure 59). About 5.1 percent have a high 

soil leaching potential and about 4.4 percent have a 

moderately high soil leaching potential in this region. 

Estimates of sediment and nutrient losses for the no-practice 

scenario (without conservation practices) demonstrate how 

vulnerability factors influence losses in the UMRB: 

 Sediment loss for the low soil runoff potential averaged 

1.4 tons per acre per year, compared to 9.4 tons per acre 

per year for the high soil runoff potential. 

 Nitrogen lost with surface runoff for the low soil runoff 

potential averaged 8 pounds per acre per year, compared 

to 40 pounds per acre per year for the high soil runoff 

potential. 
Draft June 2010 Page 96 

 Nitrogen loss in subsurface flow for the low soil leaching 

potential averaged 12 pounds per acre per year, compared 

to 53 pounds per acre per year for the high soil leaching 

potential. 

 Phosphorus lost with surface runoff for the low soil runoff 

potential averaged 3.0 pounds per acre per year, compared 

to 9.3 pounds per acre per year for the high soil runoff 

potential. 

Evaluation of Conservation Treatment 

Levels of conservation treatment in the baseline conservation 

condition were evaluated using both the level of conservation 

treatment and vulnerability factors, as shown in tables 30 

through 33. Breaking down the acres into 16 groups (four soil 

potentials and four treatment levels) reveals the following 

trends: 

 Estimates of sediment and nutrient loss for the no-practice 

scenario consistently increased from small losses for the 

low soil runoff or leaching potential to large losses for the 

high soil runoff or leaching potential. As this scenario 

represents crop production without conservation practices, 

there is no consistent relationship in loss estimates among 

the four conservation treatment levels. The differences in 

losses among conservation treatment levels reflect the 

underlying variability, which is also influenced by the 

number of acres in each group. 

 Estimates of sediment and nutrient loss for the baseline 

conservation condition, which includes conservation 

practices in use in the UMRB, exhibit a nearly consistent 

trend of decreasing loss with increasing treatment level 

within each soil runoff or leaching potential. 

 The highest losses in the baseline conservation condition 

were for groups of acres where the conservation treatment 

level was one step or more below the soil leaching or 

runoff potential. 

The evaluation of conservation treatment needs was conducted 

by identifying which of the 16 groups of acres were 

inadequately treated with respect to the soil runoff or soil 

leaching potential. To complete the evaluation, it was 

necessary to define thresholds for acceptable levels of 

sediment and nutrient loss from the field. Scientific literature 

on field research and edge-of-field monitoring in the Midwest 

provided guidance for identifying these thresholds. Model 

simulation of additional conservation practices (described in 

chapter 7) was also used to derive acceptable levels to ensure 

that the levels were possible to attain with traditional 

conservation and were agronomically feasible within the 

UMRB. 

Acceptable levels for field-level losses used in this study to 

evaluate the adequacy of conservation treatment follow: 

 Average of 2 tons per acre per year for sediment loss 

 Average of 15 pounds per acre per year for nitrogen 

lost with surface runoff (soluble and sediment 

attached) 

 Average of 25 pounds per acre per year for nitrogen 

loss in subsurface flow 

 Average of 4 pounds per acre per year for phosphorus 

lost with surface runoff (soluble and sediment 

attached) 

These acceptable levels represent field losses that are feasible 

to attain using traditional conservation treatment (nutrient 

management and soil erosion control). The percentage of acres 

in the UMRB that can attain these acceptable levels with 

additional soil erosion control and nutrient management 

practices as defined in chapter 7 are: 

 99 percent of acres for sediment loss 

 98 percent of acres for nitrogen lost with surface 

runoff 

 95 percent of acres for nitrogen loss in subsurface 

flow 

 96 percent of acres for phosphorus lost with surface 

runoff 

Acceptable levels were not used directly to identify specific 

acres that need additional treatment. Rather, acceptable levels 

were used to identify groups of acres where the conservation 

treatment level was most likely inadequate relative to the 

inherent vulnerability of the acres in that group to export soil 

or nutrients from the field. Thus, the vulnerability and 

conservation treatment condition associated with acres that 

need additional treatment is explicitly identified, providing a 

convenient framework for implementation of targeting 

strategies. 

These acceptable levels are used in this study only as an 

indication of inadequate conservation treatment at the field 

level. They are not intended to provide adequate protection of 

water quality, although for some environments they may be 

suitable for this purpose. 

Under-Treated Acres 

Two groups of acres needing treatment were identified: 1) 

under-treated acres, and 2) critical under-treated acres, a 

subset of under-treated acres. 

The percent of acres in each of the 16 groups that exceeded 

the acceptable levels was calculated, presented in tables 30 

through 33, to serve as an indication of adequate treatment for 

each group of acres. Groups of acres with more than 30 

percent of the acres exceeding acceptable levels were defined 

as under-treated acres. These are acres where field-level losses 

are most likely not being controlled adequately with the 

existing level of treatment and where additional conservation 

treatment is needed. Critical under-treated acres were defined 

as groups of acres with more than 60 percent of the acres in 

excess of acceptable levels. Critical under-treated acres 

represent the most vulnerable acres in the region, usually 

consisting of acres with a high or moderately high soil runoff 

or leaching potential. 
Draft June 2010 Page 97 

Figure 55. Conservation treatment levels for water erosion control in the baseline conservation condition, UMRB 

Criteria for water erosion control treatment levels were derived using a combination of structural practice treatment levels and residue and tillage 

management treatment levels (see figures 9 and 10). Scores were first assigned to these treatment levels as follows: High=4, Moderately high=3, 

Moderate=2, and Low=1. If slope was 2 percent or less, the water erosion control treatment level is the same as the residue and tillage management 

level. If slope was greater than 2 percent, the water erosion control treatment level is determined as follows: 

 High treatment: Sum of scores is equal to 8. (High treatment level for both structural practices and residue and tillage management practices). 

 Moderately high treatment: Sum of scores equal to 6 or 7. 

 Moderate treatment: Sum of scores equal to 4 or 5. 

 Low treatment: Sum of scores equal to 2 or 3. 

Note: About 18 percent of cropped acres in the UMRB is highly erodible land. 

Low Moderate Moderately high High

HEL 3.0 6.5 7.8 1.1

Non-HEL 6.9 23.2 12.8 38.6

0

5

10

15

20

25

30

35

40

45

Percent of cropped acres
Draft June 2010 Page 98 

Figure 56. Conservation treatment levels for nitrogen runoff control in the baseline conservation condition, UMRB 

Criteria were derived using a combination of structural practice treatment levels, residue and tillage management treatment levels, and nitrogen 

management treatment levels (see figures 9-11). Scores were first assigned to these treatment levels as follows: High=4, Moderately high=3, 

Moderate=2, and Low=1. 

If slope was 2 percent or less, the nitrogen runoff control treatment level is determined as follows: 

 High treatment: Sum of residue and tillage management score and nitrogen management score is equal to 8. (High treatment level for both 

structural practices and nitrogen management practices). 

 Moderately high treatment: Sum of scores equal to 6 or 7. 

 Moderate treatment: Sum of scores equal to 4 or 5. 

 Low treatment: Sum of scores equal to 2 or 3. 

If slope was greater than 2 percent, the nitrogen runoff control treatment level is determined as follows: 

 High treatment: Sum of structural practice score, residue and tillage management score, and nitrogen management score is equal to 12. (High 

treatment level for all three treatment types.) 

 Moderately high treatment: Sum of scores equal to 9, 10, or 11. 

 Moderate treatment: Sum of scores equal to 6, 7 or 8. 

 Low treatment: Sum of scores equal to 3, 4, or 5. 

Note: About 18 percent of cropped acres in the UMRB is highly erodible land. 

Low Moderate Moderately high High

HEL 2.5 10.1 5.7 0.1

Non-HEL 6.0 37.6 35.0 2.9

0

10

20

30

40

50

60

Percent of cropped acres
Draft June 2010 Page 99 

Figure 57. Conservation treatment levels for phosphorus runoff control in the baseline conservation condition, UMRB 

Criteria were derived using a combination of structural practice treatment levels, residue and tillage management treatment levels, and phosphorus 

management treatment levels (see figures 9, 10, and 12) in the same manner as the nitrogen runoff control treatment level. Scores were first assigned 

to these treatment levels as follows: High=4, Moderately high=3, Moderate=2, and Low=1. 

If slope was 2 percent or less, the phosphorus runoff control treatment level is determined as follows: 

 High treatment: Sum of residue and tillage management score and phosphorus management score is equal to 8. (High treatment level for both 

structural practices and phosphorus management practices). 

 Moderately high treatment: Sum of scores equal to 6 or 7. 

 Moderate treatment: Sum of scores equal to 4 or 5. 

 Low treatment: Sum of scores equal to 2 or 3. 

If slope was greater than 2 percent, the phosphorus runoff control treatment level is determined as follows: 

 High treatment: Sum of structural practice score, residue and tillage management score, and phosphorus management score is equal to 12. 

(High treatment level for all three treatment types.) 

 Moderately high treatment: Sum of scores equal to 9, 10, or 11. 

 Moderate treatment: Sum of scores equal to 6, 7 or 8. 

 Low treatment: Sum of scores equal to 3, 4, or 5. 

Note: About 18 percent of cropped acres in the UMRB is highly erodible land. 

 

Low Moderate Moderately high High

HEL 2.3 9.8 5.9 0.3

Non-HEL 8.1 32.5 30.8 10.2

0

5

10

15

20

25

30

35

40

45

Percent of cropped acres
Draft June 2010 Page 100 

Figure 58. Soil runoff potential for cropped acres in the Upper Mississippi River Basin 

Criteria for four classes of soil runoff potential were derived using a combination of soil hydrologic group, slope, and K-factor, as shown in the table 

below: 

Soil runoff potential 

Acres with 

soil hydrologic group A 

Acres with 

soil hydrologic group B 

Acres with 

soil hydrologic group C 

Acres with 

soil hydrologic 

group D 

Low All acres Slope<4 Slope<2 

Slope<2 and 

K-factor<0.28 

Moderate 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 

Moderately high None 

Slope >=4 and <=6 

and K-factor>=0.32 

Slope >=2 and <=6 

and K-factor>=0.28 Slope >=2 and <=4 

High None Slope>6 Slope>6 Slope>4 

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. 

Low Moderate Moderately high High

HEL 0.2 1.0 5.6 11.6

Non-HEL 48.9 18.8 12.8 1.1

0

10

20

30

40

50

60

Percent of cropped acres
Draft June 2010 Page 101 

Figure 59. Soil leaching potential for cropped acres in the Upper Mississippi River Basin 

Criteria for four classes of soil leaching potential were derived using a combination of soil hydrologic group, slope, and K-factor, as shown in the 

table below: 

Soil leaching potential 

Acres with 

soil hydrologic group A 

Acres with 

soil hydrologic group B 

Acres with 

soil hydrologic group C 

Acres with 

soil hydrologic 

group D 

Low None None None 

All acres except 

organic soils 

Moderate None 

Slope <=12 and 

 K-factor>=0.24 

or slope>12 

All acres except 

organic soils None 

Moderately high Slope>12 

Slope >=3 and <=12 

and K-factor<0.24 None None 

High 

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 

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, 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. 

 

Low Moderate Moderately high High

HEL 1.6 14.7 1.9 0.1

Non-HEL 20.1 54.0 2.5 5.0

0

10

20

30

40

50

60

70

80

Percent of cropped acres
Draft June 2010 Page 102 

Figure 60. Soil runoff potential for soils in the Upper Mississippi River Basin 

Note: The soil runoff potential shown in this map was derived using the criteria presented in figure 58 applied to soil characteristics for SSURGO polygons. All soils 

and land uses are represented. 

 
Draft June 2010 Page 103 

Figure 61. Soil leaching potential for soils in the Upper Mississippi River Basin 

Note: The soil leaching potential shown in this map was derived using the criteria presented in figure 59 applied to soil characteristics for SSURGO polygons. All soils 

and land uses are represented. 

 
Draft June 2010 Page 104 

Table 30. Identification of under-treated acres for sediment loss due to water erosion in the Upper Mississippi River Basin 

 Conservation treatment levels for water erosion control 

 Soil runoff potential Low Moderate 

Moderately 

high High All 

 

Estimated cropped acres 

 Low 1,518,547 7,418,626 3,970,228 15,642,150 28,549,550 

 Moderate 1,429,309 3,376,872 1,967,566 4,750,294 11,524,041 

 Moderately high 1,541,295 3,599,634 3,278,597 2,307,349 10,726,875 

 High 1,274,773 2,910,609 2,780,463 387,189 7,353,035 

 All 5,763,924 17,305,741 11,996,854 23,086,981 58,153,500 

Sediment loss estimates without conservation practices 

(no-practice scenario, average annual tons/acre/year) 

 Low 0.8 1.0 2.2 1.4 1.4 

 Moderate 2.0 2.4 3.9 1.9 2.4 

 Moderately high 3.8 3.6 5.6 3.4 4.2 

 High 8.0 9.9 9.3 11.1 9.4 

 All 3.5 3.3 5.1 1.8 3.1 

Sediment loss estimates for the baseline conservation condition (average annual tons/acre/year) 

 Low 0.5 0.4 0.5 0.3 0.4 

 Moderate 1.5 1.0 0.8 0.5 0.8 

 Moderately high 2.8 1.4 1.0 0.9 1.4 

 High 5.1 3.7 1.8 0.2 3.0 

 All 2.4 1.3 1.0 0.4 1.0 

Percent reduction in sediment loss due to conservation practices 

 Low 33% 58% 80% 80% 74% 

 Moderate 25% 58% 81% 73% 66% 

 Moderately high 26% 60% 83% 73% 67% 

 High 36% 62% 81% 99% 68% 

 All 31% 60% 81% 79% 69% 

Percent of acres in baseline conservation condition with average annual sediment loss more than 2 tons/acre 

 Low 5% 2% 1% 0% 1% 

 Moderate 25% 9% 5% 1% 7% 

 Moderately high 54% 24% 13% 10% 22% 

 High 78% 70% 32% 0% 53% 

 All 39% 19% 12% 2% 12.7% 

Estimate of under-treated acres 

 Low 0 0 0 0 0 

 Moderate 0 0 0 0 0 

 Moderately high 1,541,295 0 0 0 1,541,295 

 High 1,274,773 2,910,609 2,780,463 0 6,965,845 

 All 2,816,068 2,910,609 2,780,463 0 8,507,140 

Note: Cells below the red boundary shown for the baseline conservation condition are the acres where the level of conservation treatment is one step or more below the 

soil runoff potential. These cells consistently had the highest losses in the model simulations. 

Note: Color-shaded cells indicate under-treated acres; groups of acres with more than 30 percent of the acres exceeding acceptable levels were defined as under-treated 

acres. Darker color-shaded cells indicate critical under-treated acres; critical under-treated acres were defined as groups of acres with more than 60 percent of the acres 

in excess of acceptable levels. 

Note: Percent reductions were calculated prior to rounding the values for reporting in the table and the associated text. 

Note: Percents may not add to totals because of rounding. 
Draft June 2010 Page 105 

Table 31. Identification of under-treated acres for nitrogen lost with surface runoff (sediment attached and soluble) in the Upper 

Mississippi River Basin 

 Conservation treatment levels 

for nitrogen runoff control 

 Soil runoff potential Low Moderate 

Moderately 

high High All 

 

Estimated cropped acres 

 Low 1,505,201 12,500,814 13,411,249 1,132,287 28,549,550 

 Moderate 1,078,669 5,643,944 4,386,837 414,590 11,524,041 

 Moderately high 1,236,369 5,383,313 3,926,749 180,444 10,726,875 

 High 1,122,827 4,210,298 1,959,096 60,814 7,353,035 

 All 4,943,065 27,738,368 23,683,930 1,788,136 58,153,500 

Estimates of nitrogen lost with surface runoff without conservation practices 

(no-practice scenario, average annual pounds/acre/year) 

 Low 9 8 8 6 8 

 Moderate 17 15 14 8 15 

 Moderately high 26 22 22 18 22 

 High 48 39 36 42 40 

 All 24 17 13 9 16 

Estimates of nitrogen lost with surface runoff for the baseline conservation condition (average annual 

pounds/acre/year) 

 Low 6 5 3 3 4 

 Moderate 11 9 6 4 8 

 Moderately high 20 13 9 7 12 

 High 37 23 12 6 22 

 All 18 10 6 3 9 

Percent reduction in nitrogen lost with surface runoff due to conservation practices 

 Low 39% 44% 55% 56% 49% 

 Moderate 35% 40% 54% 55% 45% 

 Moderately high 23% 42% 59% 61% 46% 

 High 22% 41% 66% 86% 44% 

 All 27% 42% 58% 61% 46% 

Percent of acres in baseline conservation condition with average annual nitrogen lost with surface runoff 

more than 15 pounds/acre 

 Low 5% 2% 0% 0% 1% 

 Moderate 17% 12% 4% 0% 9% 

 Moderately high 53% 31% 13% 0% 27% 

 High 85% 63% 33% 0% 58% 

 All 38% 19% 6% 0% 14.6% 

Estimate of under-treated acres for nitrogen lost with surface runoff 

 Low 0 0 0 0 0 

 Moderate 0 0 0 0 0 

 Moderately high 1,236,369 5,383,313 0 0 6,619,682 

 High 1,122,827 4,210,298 1,959,096 0 7,292,220 

 All 2,359,196 9,593,610 1,959,096 0 13,911,902 

Note: Cells below the red boundary shown for the baseline conservation condition are the acres where the level of conservation treatment is one step or more below the 

soil runoff potential. These cells consistently had the highest losses in the model simulations. 

Note: Color-shaded cells indicate under-treated acres; groups of acres with more than 30 percent of the acres exceeding acceptable levels were defined as under-treated 

acres. Darker color-shaded cells indicate critical under-treated acres; critical under-treated acres were defined as groups of acres with more than 60 percent of the acres 

in excess of acceptable levels. 

Note: Percent reductions were calculated prior to rounding the values for reporting in the table and the associated text. 

Note: Percents may not add to totals because of rounding. 
Draft June 2010 Page 106 

Table 32. Identification of under-treated acres for nitrogen loss in subsurface flow in the Upper Mississippi River Basin 

 Conservation treatment levels for nitrogen management 

 Soil leaching potential Low Moderate 

Moderately 

high High All 

 

Estimated cropped acres 

 Low 2,397,634 5,032,756 3,838,671 1,354,476 12,623,538 

 Moderate 8,915,433 17,638,789 10,065,116 3,340,532 39,959,870 

 Moderately high 593,742 957,979 724,363 278,295 2,554,380 

 High 257,256 1,380,144 915,952 462,360 3,015,713 

 All 12,164,066 25,009,669 15,544,103 5,435,663 58,153,500 

Estimates of nitrogen loss in subsurface flow without conservation practices 

(no-practice scenario, average annual pounds/acre/year) 

 Low 19 11 10 9 12 

 Moderate 32 24 17 12 23 

 Moderately high 61 39 26 12 38 

 High 83 58 41 47 53 

 All 32 24 17 14 23 

Estimates of nitrogen loss in subsurface flow for the baseline conservation condition (average annual 

pounds/acre/year) 

 Low 22 14 7 7 13 

 Moderate 33 26 11 8 23 

 Moderately high 52 34 15 9 30 

 High 79 56 25 25 44 

 All 33 26 11 9 22 

Percent reduction in nitrogen loss in subsurface flow due to conservation practices 

 Low -19% -28% 31% 27% -6% 

 Moderate -4% -8% 33% 33% 2% 

 Moderately high 14% 14% 41% 28% 20% 

 High 4% 2% 40% 48% 17% 

 All -3% -7% 34% 36% 5% 

Percent of acres in baseline conservation condition with average annual nitrogen loss in subsurface flow more 

than 25 pounds/acre 

 Low 21% 13% 2% 0% 10% 

 Moderate 42% 39% 4% 1% 28% 

 Moderately high 57% 52% 11% 0% 36% 

 High 98% 89% 24% 9% 58% 

 All 40% 37% 5% 1% 26% 

Estimate of under-treated acres for nitrogen loss in subsurface flow 

 Low 0 0 0 0 0 

 Moderate 8,915,433 17,638,789 0 0 26,554,222 

 Moderately high 593,742 957,979 0 0 1,551,721 

 High 257,256 1,380,144 0 0 1,637,400 

 All 9,766,431 19,976,913 0 0 29,743,344 

Note: Cells below the red boundary shown for the baseline conservation condition are the acres where the level of conservation treatment is one step or more below the 

soil leaching potential. These cells consistently had the highest losses in the model simulations. 

Note: Color-shaded cells indicate under-treated acres; groups of acres with more than 30 percent of the acres exceeding acceptable levels were defined as under-treated 

acres. Darker color-shaded cells indicate critical under-treated acres; critical under-treated acres were defined as groups of acres with more than 60 percent of the acres 

in excess of acceptable levels. 

Note: Percent reductions were calculated prior to rounding the values for reporting in the table and the associated text. 

Note: Percents may not add to totals because of rounding. 
Draft June 2010 Page 107 

Table 33. Identification of under-treated acres for phosphorus lost with surface runoff (sediment attached and soluble) in the Upper 

Mississippi River Basin 

 Conservation treatment levels 

for phosphorus runoff control 

 Soil runoff potential Low Moderate 

Moderately 

high High All 

 

Estimated cropped acres 

 Low 2,231,503 10,901,871 10,918,831 4,497,345 28,549,550 

 Moderate 1,356,846 4,708,559 4,431,296 1,027,340 11,524,041 

 Moderately high 1,430,747 4,880,731 3,975,252 440,145 10,726,875 

 High 1,058,478 4,101,378 2,073,750 119,429 7,353,035 

 All 6,077,574 24,592,538 21,399,130 6,084,259 58,153,500 

Phosphorus lost with surface runoff without conservation practices 

(no-practice scenario, average annual pounds/acre/year) 

 Low 5.3 3.1 2.7 2.4 3.0 

 Moderate 5.9 4.9 4.9 4.2 4.9 

 Moderately high 12.6 6.5 5.8 6.0 7.1 

 High 13.8 9.1 7.4 10.6 9.3 

 All 8.6 5.1 4.2 3.1 4.9 

Phosphorus lost with surface runoff for the baseline conservation condition (average annual pounds/acre/year) 

 Low 3.8 2.0 1.0 0.6 1.5 

 Moderate 4.3 3.1 1.7 1.2 2.5 

 Moderately high 9.6 3.9 1.9 1.6 3.8 

 High 10.1 4.8 2.0 1.0 4.7 

 All 6.4 3.0 1.4 0.8 2.5 

Percent reduction in phosphorus lost with surface runoff due to conservation practices 

 Low 29% 35% 65% 74% 49% 

 Moderate 28% 37% 65% 72% 49% 

 Moderately high 23% 41% 68% 72% 46% 

 High 27% 47% 72% 90% 49% 

 All 26% 40% 67% 75% 48% 

Percent of acres in baseline conservation condition with average annual phosphorus lost with surface runoff 

more than 4 pounds/acre 

 Low 23% 12% 1% 0% 7% 

 Moderate 42% 21% 3% 2% 15% 

 Moderately high 79% 24% 6% 5% 24% 

 High 84% 43% 9% 0% 39% 

 All 51% 21% 3% 1% 16% 

Estimate of under-treated acres for phosphorus lost with surface runoff 

 Low 0 0 0 0 0 

 Moderate 1,356,846 0 0 0 1,356,846 

 Moderately high 1,430,747 0 0 0 1,430,747 

 High 1,058,478 4,101,378 0 0 5,159,856 

 All 3,846,071 4,101,378 0 0 7,947,449 

Note: Cells below the red boundary shown for the baseline conservation condition are the acres where the level of conservation treatment is one step or more below the 

soil runoff potential. These cells consistently had the highest losses in the model simulations. 

Note: Color-shaded cells indicate under-treated acres; groups of acres with more than 30 percent of the acres exceeding acceptable levels were defined as under-treated 

acres. Darker color-shaded cells indicate critical under-treated acres; critical under-treated acres were defined as groups of acres with more than 60 percent of the acres 

in excess of acceptable levels.

Note: Percent reductions were calculated prior to rounding the values for reporting in the table and the associated text. 

Note: Percents may not add to totals because of rounding. 

 
Draft June 2010 Page 108 

Table 34. Resource concerns needing treatment in the Upper Mississippi River Basin 

Reasons for treatment need 

Estimated acres 

needing treatment 

Percent 

of total

All under-treated acres (62 percent of cropped acres) 

Nitrogen leaching only 20,680,259 58

Sediment, nitrogen and phosphorus runoff, and nitrogen leaching 3,802,270 11

Nitrogen runoff and nitrogen leaching 3,102,268 9

Sediment, nitrogen runoff and phosphorus runoff 2,198,556 6

Nitrogen runoff only 1,716,701 5

Other combinations, each including either nitrogen or phosphorus 4,452,936 12

Total 35,952,991 100

Critical under-treated acres (15 percent of cropped acres) 

Sediment, nitrogen and phosphorus runoff, and nitrogen leaching 3,645,703 43

Sediment, nitrogen runoff, and phosphorus runoff 1,828,798 22

Nitrogen leaching only 1,630,738 19

Nitrogen runoff and nitrogen leaching 563,565 7

Nitrogen runoff, phosphorus runoff, and nitrogen leaching 310,871 4

Other combinations 478,108 6

Total 8,457,783 100

 Note: This table summarizes the under-treated acres identified in tables 30-33 and reports the joint set of acres that need treatment according to each resource concern. 

Note: Percents may not add to totals because of rounding. 

High levels of treatment were shown by model simulations to 

provide good protection on the most vulnerable acres. Less 

vulnerable acres were often adequately treated with a low, 

moderate, or moderately high level of conservation treatment. 

Many of the more vulnerable acres with less conservation 

treatment, however, require additional conservation practices: 

 8.5 million acres (15 percent of cropped acres) require 

additional treatment for sediment loss due to water 

erosion (table 30). 

 13.9 million acres (24 percent of cropped acres) require 

additional treatment for nitrogen lost with surface runoff 

(table 31). 

 29.7 million acres (51 percent of cropped acres) require 

additional treatment for nitrogen loss in subsurface flow 

(table 32). 

 7.9 million acres (14 percent of cropped acres) require 

additional treatment for phosphorus lost with surface 

runoff (table 33). 

About 63 percent of the under-treated acres need additional 

treatment for only one of the four resource concerns, usually 

nitrogen leaching (table 34). For critical under-treated acres, 

79 percent need additional treatment for multiple resource 

concerns. 

After accounting for acres that need treatment for multiple 

resource concerns, the evaluation of treatment needs for the 

UMRB determined the following (table 34): 

 36 million acres (62 percent of cropped acres) are undertreated for one or more of the four resource concerns that 

were evaluated: 

o all require additional treatment for either nitrogen or 

phosphorus, 

o 58 percent require additional treatment only for 

nitrogen loss in subsurface flow, 

o 9 percent require additional treatment for nitrogen 

runoff and leaching, and 

o 17 percent require additional treatment for sediment 

loss, nitrogen runoff, and phosphorus runoff. 

 8.5 million of these acres (15 percent of cropped acres) 

are critical under-treated acres, consisting of the most 

vulnerable acres in the region: 

o 43 percent require additional treatment for all four 

resource concerns, 

o 22 percent require additional treatment for sediment 

loss, nitrogen lost with surface runoff, and

phosphorus lost with surface runoff, and 

o 19 percent require additional treatment only for 

nitrogen loss in subsurface flow. 

The distribution of under-treated acres among the 14 

subbasins within the UMRB is presented in table 35. 

Percentages of the under-treated acres in the UMRB that are in 

each subbasin are close to the same percentages of the 

region’s cultivated cropland in each subbasin, indicating that 

under-treated acres are spread proportionately throughout the 

region. Critical under-treated acres, however, are often 

disproportionately distributed, with higher concentrations in 

some regions than others relative to the percentage of cropped 

acres. 
Draft June 2010 Page 109 

The breakdown of under-treated acres by cropping system also 

showed a proportionate distribution of under-treated acres 

among cropping systems, shown in table 36. For the critical 

under-treated acres, however, a disproportionately higher 

percentage occurs for two cropping systems—hay crop mixes 

and continuous corn—indicating that these two cropping 

systems tend to occur more frequently on the more vulnerable 

acres in the region. 

Losses for under-treated acres are much higher, on average, 

than losses for adequately treated acres, as shown in table 37. 

For example, sediment loss in the baseline conservation 

condition averages 2.8 tons per acre per year for critical undertreated acres, compared to 0.8 ton per acre per year for noncritical under-treated acres and only 0.5 ton per acre for the 

remaining acres. Total nitrogen loss averages 65 pounds per 

acre for the critical under-treated acres and 45 pounds per acre 

for the non-critical under-treated acres, compared to only 28 

pounds per acre for the remaining acres. 

 
Draft June 2010 Page 110 

Table 35. Under-treated acres for the 14 subbasins in the Upper Mississippi River Basin

 Critical under-treated acres All under-treated acres 

Subbasin 

code Subbasin name 

Percent 

of 

cropped 

acres in 

UMRB Acres 

Percent 

of acres 

in 

UMRB 

Percent of 

cultivated 

cropland 

acres in 

subbasin Acres 

Percent 

of acres 

in 

UMRB 

Percent of 

cultivated 

cropland 

acres in 

subbasin 

0701 Mississippi Headwaters 5 734,021 9 27 1,606,435 4 60 

0702 Minnesota River Basin 13 647,144 8 9 4,299,339 12 59 

0703 St. Croix River Basin 1 149,890 2 30 278,811 1 55 

0704 Upper Mississippi-Black-Root 5 770,960 9 29 1,996,869 6 74 

0705 Chippewa River Basin 2 385,691 5 44 701,957 2 80 

0706 Upper Mississippi-MaquoketaPlum 4 585,939 7 23 2,068,665 6 79 

0707 Wisconsin River Basin 2 480,501 6 35 803,021 2 59 

0708 Upper Mississippi-Iowa-SkunkWapsipinicon 18 1,448,436 17 14 6,498,400 18 63 

0709 Rock River Basin 7 706,938 8 17 2,940,668 8 70 

0710 Des Moines River Basin 11 367,660 4 6 3,029,770 8 48 

0711 Upper Mississippi-Salt 5 619,743 7 22 1,672,290 5 60 

0712 Upper Illinois River Basin 7 696,545 8 17 2,326,329 6 58 

0713 Lower Illinois River Basin 14 551,060 7 7 5,493,048 15 66 

0714 Upper Mississippi-KaskaskiaMeramec 7 313,254 4 8 2,237,389 6 55 

Total 100 8,457,782 100 15 35,952,991 100 62 

Note: Percents may not add to totals because of rounding. 

Table 36. Under-treated acres by cropping system in the Upper Mississippi River Basin

 Critical under-treated acres All under-treated acres 

Subbasin name 

Percent 

of 

cropped 

acres in 

UMRB Acres 

Percent 

of acres 

in 

UMRB 

Percent of 

cultivated 

cropland acres in 

cropping system Acres 

Percent 

of acres 

in 

UMRB 

Percent of 

cultivated 

cropland acres in 

cropping system 

Corn and soybean only 74 4,813,110 57 11 26,019,824 72 61 

Corn only 9 1,172,666 14 23 3,584,729 10 71 

Hay-crop mix 6 1,244,373 15 34 2,654,540 7 73 

Corn and soybean with close 

grown crops 4 289,622 3 14 1,497,667 4 70 

Soybean only 3 158,351 2 11 348,400 1 23 

Soybean and wheat only 1 164,093 2 21 408,079 1 52 

Corn and close grown crops 1 311,407 4 41 623,610 2 83 

Remaining mix of crops 2 304,161 4 23 816,143 2 63 

Total 100 8,457,782 100 15 35,952,991 100 62 

Note: Percents may not add to totals because of rounding. 

 
Draft June 2010 Page 111 

Table 37. Baseline conservation condition model simulation results for subsets of under-treated and adequately treated acres in the 

Upper Mississippi River Basin 

Model simulated outcome 

Critical 

under-treated 

acres 

Non-critical 

undertreated acres Adequately 

treated acres All acres 

Cultivated cropland acres in subset 8,457,782 27,495,208 22,200,509 58,153,500 

Percent of acres 15% 47% 38% 100% 

Water flow 

Average annual surface runoff (inches) 3.8 3.5 4.7 4.0 

Average annual subsurface water flow (inches) 7.7 7.0 5.9 6.7 

Erosion and sediment loss 

Average annual wind erosion (tons/acre) 0.3 0.2 0.2 0.2 

Average annual sheet and rill erosion (tons/acre) 2.4 1.0 0.6 1.0 

Average annual sediment loss at edge of field due to 

water erosion (tons/acre) 2.8 0.8 0.5 1.0 

Soil organic carbon 

Average annual change in soil organic carbon, including 

loss of carbon with wind and water erosion 

(pounds/acre) -53 109 68 70 

Nitrogen loss 

Nitrogen applied (pounds/acre) 107 98 68 88 

Nitrogen in crop yield removed at harvest (pounds/acre) 105 107 109 108 

Total nitrogen loss for all pathways except harvest 

(pounds/acre) 65 45 28 41 

Average annual loss of nitrogen through volatilization 

(pounds/acre) 7 7 6 7 

Average annual nitrogen returned to the atmosphere 

through denitrification processes (pounds/acre) 3 2 2 2 

Average annual loss of nitrogen with surface runoff, 

including waterborne sediment (pounds/acre) 20 7 6 9 

Average annual nitrogen loss in subsurface flow 

(pounds/acre) 32 27 12 22 

Phosphorus loss 

Phosphorus applied (pounds/acre) 26.9 23.2 19.5 22.3 

Total phosphorus loss for all pathways except harvest 

(pounds/acre) 5.9 2.7 2.2 3.0 

Loss of phosphorus with surface runoff, including 

waterborne sediment (pounds/acre) 5.4 2.3 1.8 2.5 

Pesticide loss 

Average annual mass loss of pesticides for all pathways 

(grams of active ingredient/hectare) 12.7 7.2 8.2 8.4 

Average annual surface water pesticide risk indicator for 

aquatic ecosystem 2.4 2.6 2.7 2.6 

Average annual surface water pesticide risk indicator for 

humans 0.5 0.3 0.5 0.4 

Note: The values reported in this table for the three subsets of acres are influenced by differences in precipitation, slope, and inherent soil vulnerability in addition to the 

differences in conservation treatment. 
Draft June 2010 Page 112 

Chapter 7 

Assessment of Potential Gains from 

Further Conservation Treatment 

Four conservation treatment scenarios were simulated to 

evaluate the potential gains from further conservation 

treatment in the UMRB: 

 Treatment of the 8.5 million critical under-treated acres 

with water erosion control practices. 

 Treatment of all 36 million under-treated acres with water 

erosion control practices. 

 Treatment of the 8.5 million critical under-treated acres 

with nutrient management practices in addition to water 

erosion control practices to address nutrient losses. 

 Treatment of all 36 million under-treated acres with 

nutrient management practices in addition to water 

erosion control practices to address nutrient losses. 

The simulated levels of conservation treatment were designed 

to add the additional practices needed to complete the existing 

suite of practices so as to reduce sediment and nutrient losses 

at the edge of the field to acceptable levels. The existing 

practices were augmented with additional practices to— 

 avoid or limit the potential for loss by using nutrient 

management practices (appropriate rate, timing, and

method) on all crops in the rotation; 

 control overland flow where needed; and 

 trap materials leaving the field using appropriate edge-offield mitigation where absent. 

The simulated additional treatment consists of traditional 

conservation practices and treatment options that have been 

implemented over the past 10 years and would be expected to 

be found in current NRCS conservation plans. The simulated 

treatment levels are intended to maintain the production 

capacity within the region to produce crops for food, fiber, 

forage, and fuel. 

The specific conservation practices used in the simulated 

treatments are not intended to be a prescription for how to 

construct conservation plans, but rather are a general 

representation of sets or suites of conservation practices that 

could be used to address multiple resource concerns. In actual 

planning situations a variety of alternative practice scenarios 

would be presented to the producer and selections would be 

based on the level of treatment need, cost of conservation 

implementation, impact on production goals, and preferences 

of the farm operator. 

The level of conservation treatment is simulated to show 

potential environmental benefits, but is not designed to 

achieve specific environmental protection goals. Treatment 

scenarios were also not designed to represent actual program 

or policy options for the UMRB. Economic and programmatic 

aspects--such as producer costs, conservation program costs, 

and capacity to deliver the required technical assistance--were 

not considered in the design of the treatment scenarios. 

Conservation crop rotations were not included in the treatment 

scenarios because of the criteria to maintain crop acres and 

preserve current market value and yield. Nevertheless, crop 

rotations that are conducted specifically for the purpose of 

reducing average annual losses of sediment and nutrients from 

farm fields have a high potential to further improve crop 

nutrient efficiency and reduce contaminant loadings. 

For the same reason, long-term conserving cover was also not 

included in the treatment scenarios. Long-term conserving 

cover represents the ultimate conservation treatment for acres 

that are highly vulnerable to sediment and nutrient loss. 

Enrolling more cultivated cropland acres in programs that 

provide the economic incentives for long-term conserving 

cover may be necessary in some areas to meet watershed goals 

for environmental protection. 

Pesticide management was also not addressed in the treatment 

scenarios. While erosion control practices influence pesticide 

loss, significant reductions in pesticide risk within the region 

will require more intensive Integrated Pest Management (IPM) 

practices, including pesticide substitutions. Simulation of 

additional IPM and any associated pesticide substitutions is 

very site specific and requires more information about the 

sample fields than was available from the farmer survey. 

Simulation of Additional Water Erosion 

Control Practices 

Erosion and surface water runoff treatment consists of 

structural and vegetative practices that slow runoff water and 

capture contaminants that it may carry. Practices were added 

where needed (summarized in table 38) according to the 

following rules. 

 In-field mitigation: 

o Terraces were added to all sample points with slopes 

greater than 6 percent, and to those with slopes 

greater than 4 percent and a high potential for 

excessive runoff (hydrologic soil groups C or D). 

Although terraces may be too expensive or 

impractical to implement in all cases, they serve here 

as a surrogate for other practices that control surface 

water runoff. 

o Contouring or stripcropping was added to all other 

fields that did not already have those practices and 

did not have terraces. 

o Concentrated flow practices were not applied since 

they occur on unique landscape situations within the 

field; landscape data other than slope and slope 

length were not available for CEAP sample points. 
Draft June 2010 Page 113 

 Edge-of-field mitigation: 

o Fields adjacent to water received a riparian buffer, if 

one was not already present. 

o Fields not adjacent to water received a filter strip, if 

one was not already present. 

In addition, the implementation of structural and vegetative 

practices is simulated by an adjustment in the land condition 

parameter used to estimate the NRCS Runoff Curve Number 

(RCN). The RCN is an empirical parameter used in surface 

hydrology for predicting direct runoff or infiltration. The 

hydrologic condition (a component in the determination of the 

RCN) was adjusted from “poor” to “good” for sample points 

where these additional practices were simulated. 

Cover crops were not added since it was unrealistic to expect 

farmers to adopt cover crops on all fields in the UMRB. Less 

than 1 percent of the acres meet criteria for use of a cover crop 

in this region. Similarly, tillage management was not altered in 

the simulation of conservation treatment because of the 

widespread use of residue and tillage management in the 

region. 

Simulation of Additional Nutrient 

Management Practices 

The nutrient management treatment scenario consists of 

additional nutrient management practices where needed in 

addition to the water erosion control practices. The nutrient 

management practices simulated the application of nutrients at 

an appropriate rate, in an appropriate form, at appropriate 

times, and using an appropriate method to provide sufficient 

nutrients for crop growth while minimizing losses to the 

environment. Simulation of nutrient management required 

changes to nutrient applications for one or more crops on all 

but about 7 percent of the acres (see table 9). 

Specific rules for application timing 

The goal for appropriate timing is to apply nutrients close to 

the time when the plant is likely to require them, thereby 

minimizing the opportunity for loss from the field. Rules for 

the timing of nutrient applications (both nitrogen and 

phosphorus) are: 

o All commercial fertilizer applications were adjusted to 14 

days prior to planting, except for acres susceptible to 

leaching loss. 

o For acres susceptible to leaching loss (hydrologic soil 

group A, soils with sandy textures, or tile drained fields), 

nitrogen was applied in split applications, with 25 percent 

of the total application 14 days before planting and 75 

percent 30 days after planting. 

o Manure applications during winter months (December, 

January, February, and March) were moved to 14 days 

pre-plant or April 1, whichever occurs first. This rule 

allows for late March applications of manure in the 

warmer climates of the UMRB. April 1 is near the period 

when the soils warm and become biologically active. 

However, this late date could begin to pressure manure 

storage capacities and it is recognized that this could 

create storage problems. 

About 28 million acres (48%) in the UMRB receive fertilizer 

applications in the fall for at least one spring-planted row crop 

in the rotation. The only fall application of nutrients simulated 

in the nutrient management treatment scenario was for fall 

seeded crops that received a starter fertilizer at planting time. 

Table 38. Summary of additional structural practices simulated for under-treated acres to assess the potential for gains from additional 

conservation treatment in the Upper Mississippi River Basin

 

Critical under-treated 

acres 

Non-critical undertreated acres All under-treated acres 

Additional practice 

Treated 

acres 

Percent 

of total 

Treated 

acres 

Percent 

of total 

Treated 

acres 

Percent 

of total 

Overland flow practice only 0 0 263,860 1 263,860 1 

Terrace only 320,703 2 91,738 <1 412,441 1 

Filter only 2,254,496 15 8,289,750 40 10,544,246 29 

Filter plus overland flow practice 3,362,564 22 5,208,368 25 8,570,931 24 

Filter plus Terrace 4,917,831 32 805,735 4 5,723,566 16 

Buffer only 1,135,468 7 3,131,436 15 4,266,904 12 

Buffer plus overland flow 

practice 1,232,209 8 1,787,747 9 3,019,956 8 

Buffer plus Terrace 1,776,389 12 427,643 2 2,204,032 6 

 One or more additional practices 14,999,660 99 20,006,276 96 35,005,936 97 

No structural practices 173,992 1 827,301 4 1,001,293 3 

Total 15,173,653 100 20,833,577 100 36,007,229 100 

Note: Percents may not add to totals because of rounding. 
Draft June 2010 Page 114 

Specific rules for method of application 

If the method of application was other than incorporation then 

fertilizer and manure applications became incorporated. 

Incorporation reduces the opportunity for nutrients on the soil 

surface to be carried away in the soluble form or attached to 

eroding particles. For manure applications on no-till fields, if 

the manure had been broadcast applied it was changed to 

injected or placed under the soil surface. Manure of solid 

consistency was incorporated by disking without regard to the 

tillage management type. If the tillage type had been originally 

no-till, the incorporation of the manure changed the tillage 

type to mulch tillage. 

Specific rules for the form of application 

If the tillage type was no-till, commercial fertilizer was 

changed to a form that could be knifed or injected below the 

soil surface. The change in form did not change the ammonia 

or nitrate ratio of the fertilizer. In some cases, incorporation of 

manure also required a change in the manure form to preserve 

the beneficial effects of tillage and residue management. 

Specific rules for the rate of nutrient applied 

All nitrogen application rates for all crops were reduced to 1.2 

times the crop removal rate. The 1.2 ratio is in the range of 

rates recommended by many of the Land Grant Universities. 

This rate replaces some of the environmental losses that occur 

during the cropping season, and also accounts for the savings 

in nutrients due to implementation of water erosion control 

practices. 

For phosphorus, the application rates were adjusted to be 

equal to 1.1 times the amount of phosphorus removed in the 

crop at harvest over the crop rotation. 

Potential for Field-Level Gains 

Treatment of the 8.5 million critical under-treated 

acres

According to the model simulation, treatment of the 8.5 

million most vulnerable under-treated acres with water erosion 

control practices would nearly eliminate sediment loss for 

these acres and dramatically reduce nitrogen and phosphorus 

lost with surface runoff, as shown in table 39. 

Sediment loss would be reduced to an annual average of about 

0.1 ton per acre per year for these acres, a 95-percent 

reduction. Nitrogen lost with surface runoff would be reduced 

to 3 pounds per acre per year on average (84-percent 

reduction), and phosphorus lost with surface runoff would be 

reduced to 1.8 pounds per acre per year (67-percent 

reduction). However, the re-routing of surface water to 

subsurface flow would reduce nitrogen loss in subsurface flow 

by only 1 percent, on average, for these acres. 

The addition of nutrient management had little additional 

effect on sediment loss or nitrogen lost with surface runoff, 

but was effective in reducing nitrogen loss in subsurface flows 

and phosphorus lost with surface runoff (table 39). Nitrogen 

loss in subsurface flow for these acres would be reduced 57 

percent compared to losses simulated for the baseline 

conservation condition. Phosphorus lost with surface runoff 

would be reduced to an average loss of about 1 pound per 

acre, representing an 82 percent reduction compared to the 

baseline condition for these acres. 

These results support the conclusion drawn from the 

assessment of the effects of conservation practices that 

nutrient management practices need to be paired with erosion 

control practices to obtain net reductions in the loss of soluble 

nutrients. 

Table 40 presents estimates of how treatment of just the 8.5 

million most vulnerable acres in the region would reduce 

overall edge-of-field losses for the region as a whole. These 

results were obtained by combining treatment scenario model 

results for the 8.5 million acres with model results from the 

baseline conservation condition for the remaining acres. 

Treating the 8.5 million critical under-treated acres with soil 

erosion control practices and nutrient management practices 

would, for the region as a whole— 

 reduce sediment loss in the region by 40 percent on 

average, compared to the baseline conservation condition; 

 reduce total nitrogen loss by 14 percent: 

o reduce nitrogen lost with surface runoff (sediment 

adsorbed and soluble) by 29 percent, and 

o reduce nitrogen loss in subsurface flow by 12 

percent; 

 reduce phosphorus lost with surface runoff (sediment 

adsorbed and soluble) by 25 percent, and 

 reduce environmental risk from loss of pesticide residues 

by about 4 to 5 percent. 

 
Draft June 2010 Page 115 

Table 39. Conservation practice effects for additional treatment of 8.5 million critical under-treated acres in the Upper Mississippi 

River Basin 

Model simulated outcome 

Baseline 

conservation 

condition 

Treatment with erosion control 

practices 

Treatment with erosion control 

and nutrient management 

practices 

Average annual 

amount 

Average 

annual amount 

Percent 

reduction 

Average 

annual amount 

Percent 

reduction 

Water flow 

Surface water runoff (inches) 3.8 3.1 20% 3.1 20% 

Subsurface water flow (inches) 7.7 8.1 -5% 8.2 -6% 

Erosion and sediment loss 

Wind erosion (tons/acre) 0.3 0.3 10% 0.3 13% 

Sheet and rill erosion (tons/acre) 2.4 0.5 79% 0.5 80% 

Sediment loss at edge of field due to water 

erosion (tons/acre) 2.8 0.1 95% 0.1 95% 

Soil organic carbon 

Change in soil organic carbon, including 

loss of carbon with wind and water erosion 

(pounds/acre) -53 71 -- 62 -- 

Nitrogen 

Nitrogen applied (pounds/acre) 106.7 102.0 4%* 69.7 35% 

Nitrogen in crop yield removed at harvest 

(pounds/acre) 105.0 102.6 2%* 98.1 7% 

Total nitrogen loss for all pathways except 

harvest (pounds/acre) 64.6 47.2 27% 25.7 60% 

Loss of nitrogen with surface runoff, 

including waterborne sediment 

(pounds/acre) 20.0 3.2 84% 2.7 86% 

Nitrogen loss in subsurface flow 

(pounds/acre) 31.8 31.5 1% 13.6 57% 

Phosphorus 

Phosphorus applied (pounds/acre) 26.9 26.1 3% 19.3 28% 

Total phosphorus loss for all pathways 

except harvest (pounds/acre) 5.9 2.3 61% 1.4 77% 

Loss of phosphorus with surface 

runoff, including waterborne sediment 

(pounds/acre) 5.4 1.8 67% 1.0 82% 

Pesticide loss 

Mass loss of pesticides for all pathways 

(grams of active ingredient/hectare) 12.7 5.7 55% 5.7 55% 

Surface water pesticide risk indicator for 

aquatic ecosystem 2.4 1.7 28% 1.7 28% 

Surface water pesticide risk indicator for 

humans 0.5 0.3 29% 0.3 30% 

* Total nitrogen applied was less in the treatment scenario than in the baseline because a small fraction of the field was removed from production to 

simulate use of additional edge-of-field buffer and filtering practices. This also explains the small decrease in nitrogen in the crop yield at harvest. 

Note: Values reported in this table are for the 8.5 million critical under-treated acres only. Percent reductions are with respect to the baseline 

conservation condition. 

Note: Percent reductions were calculated prior to rounding the values for reporting in the table and the associated text. 
Draft June 2010 Page 116 

Table 40. Conservation practice effects for the region as a whole* after additional treatment of 8.5 million critical under-treated acres 

in the Upper Mississippi River Basin 

Model simulated outcome 

Baseline 

conservation 

condition 

Treatment with erosion control 

practices 

Treatment with erosion control 

and nutrient management 

practices 

Average annual 

amount 

Average 

annual amount 

Percent 

reduction 

Average 

annual amount 

Percent 

reduction 

Water flow 

Surface water runoff (inches) 4.0 3.9 3% 3.9 3% 

Subsurface water flow (inches) 6.7 6.7 -1% 6.7 -1% 

Erosion and sediment loss 

Wind erosion (tons/acre) 0.2 0.2 2% 0.2 2% 

Sheet and rill erosion (tons/acre) 1.0 0.8 26% 0.8 26% 

Sediment loss at edge of field due to water 

erosion (tons/acre) 1.0 0.6 40% 0.6 40% 

Soil organic carbon 

Change in soil organic carbon, including 

loss of carbon with wind and water erosion 

(pounds/acre) 70 88 -- 87 -- 

Nitrogen 

Nitrogen applied (pounds/acre) 87.8 87.2 1% 82.5 6% 

Nitrogen in crop yield removed at harvest 

(pounds/acre) 107.6 107.2 0% 106.6 1% 

Total nitrogen loss for all pathways except 

harvest (pounds/acre) 41.3 38.8 6% 35.7 14% 

Loss of nitrogen with surface runoff, 

including waterborne sediment 

(pounds/acre) 8.6 6.1 29% 6.1 29% 

Nitrogen loss in subsurface flow 

(pounds/acre) 21.8 21.8 0% 19.2 12% 

Phosphorus 

Phosphorus applied (pounds/acre) 22.3 22.2 1% 21.2 5% 

Total phosphorus loss for all pathways 

except harvest (pounds/acre) 3.0 2.4 18% 2.3 22% 

Loss of phosphorus with surface 

runoff, including waterborne sediment 

(pounds/acre) 2.5 2.0 21% 1.9 25% 

Pesticide loss 

Mass loss of pesticides for all pathways 

(grams of active ingredient/hectare) 8.4 7.4 12% 7.4 12% 

Surface water pesticide risk indicator for 

aquatic ecosystem 2.6 2.5 4% 2.5 4% 

Surface water pesticide risk indicator for 

humans 0.4 0.4 5% 0.4 5% 

* Results presented for the region as a whole combine model output for the 8.5 million treated acres with model results from the baseline 

conservation condition for the remaining acres. 

Note: Percent reductions are with respect to the baseline conservation condition. 

Note: Percent reductions were calculated prior to rounding the values for reporting in the table and the associated text. 
Draft June 2010 Page 117 

Treatment of all 36 million under-treated acres.

Simulation of additional conservation treatment of all 36 

million under-treated acres showed that, while per-acre 

sediment and nutrient loss reductions due to practices would 

be less on average than per-acre reductions for the 8.5 million 

most vulnerable under-treated acres, the percent reductions for 

the region as a whole at this level of treatment would be much 

higher. 

Simulation results for only the 36 million under-treated acres 

are presented in table 41, and results for the region as a whole 

are presented in table 42. Treating all 36 million under-treated 

acres with soil erosion control practices and nutrient 

management practices would, for the region as a whole (table 

42)— 

 reduce sediment loss in the region by 74 percent on 

average, compared to the baseline conservation condition; 

 reduce total nitrogen loss by 43 percent: 

o reduce nitrogen lost with surface runoff (sediment 

attached and soluble) by 61 percent, and 

o reduce nitrogen loss in subsurface flow by 48 

percent; 

 reduce phosphorus lost with surface water runoff by 57 

percent; 

 reduce environmental risk from loss of pesticide residues 

by 2 to 15 percent. 

Comparison of treatment scenario results 

The distributions of sediment and nutrient losses for the two 

levels of treatment are compared to the baseline conservation 

condition in the UMRB in figures 62-66. For perspective, the 

distribution of loss estimates if no conservation practices were 

in use, represented by the no-practice scenario, is also shown. 

The distributions show how the number of acres with high 

losses could be reduced dramatically in the region, by 

preferentially treating the under-treated acres. For example, 12 

percent of the acres in the UMRB exceed an annual average 

loss of sediment of 2 tons per acre per year in the baseline 

conservation condition. Model simulations suggest that 

treating the most vulnerable of the under-treated acres (8.5 

million acres) with water erosion control practices would 

reduce the acres exceeding sediment loss of 2 tons per acre per 

year to 5 percent. Expanding the treatment to include all 

under-treated acres (36 million acres) would further reduce the 

acres exceeding annual sediment loss of 2 tons per acre to less 

than 1 percent. 

Similar effects of additional treatment are shown for nitrogen 

and phosphorus lost with surface runoff. Treatment of critical 

under-treated acres with water erosion control and nutrient 

management would reduce the acres exceeding 15 pounds per 

acre of nitrogen lost with surface runoff to 8 percent (figure 

64); treatment of all 36 million under-treated acres would 

reduce the acres exceeding 15 pounds per acre to 2 percent. 

Acres exceeding 4 pounds per acre of phosphorus lost with 

surface runoff would be reduced to 9 percent by treating the 

critical acres and reduced to 4 percent by treating all undertreated acres. 

For nitrogen loss in subsurface flow pathways, however, 

treatment of all 36 million under-treated acres would be 

required to reduce the overall regional edge-of-field losses 

significantly (figure 65). About 26 percent of the acres in the 

region have nitrogen loss in subsurface flow greater than 25 

pounds per acre per year for the baseline conservation 

condition. This is in part the result of the use of soil erosion 

control practices with no or only partial use of nutrient 

management practices. Treating the 8.5 million critical undertreated acres with nutrient management practices would 

reduce this percentage to only 21 percent. However, treatment 

of all 36 million under-treated acres would reduce the 

percentage to 5 percent. 

Soil organic carbon was minimally affected by the additional 

soil erosion control and nutrient management practices, 

largely because of savings of carbon that would otherwise 

have been lost from the field through wind and water erosion. 

Figure 67 shows that the percentage of acres building soil 

organic carbon would increase from 75 percent for the 

baseline conservation condition to 82 percent with additional 

conservation treatment of the 36 million under-treated acres. 

One of the objectives in constructing the treatment scenarios 

was to maintain the level of regional crop production. The 

removal of nitrogen at harvest serves as a useful proxy for 

crop yields and allows for aggregation over the mix of crops. 

The average annual amount of nitrogen removed at harvest 

was reduced about 7 percent for the 36 million acres treated 

with additional soil erosion control and nutrient management 

practices (table 41), which represents a 4-percent reduction for 

the region as a whole (table 42). Figure 68 shows that the 

distribution of nitrogen removed at harvest is slightly lower 

for the treatment scenarios but otherwise was similar to the 

distribution for the baseline conservation condition. 

Emerging technologies for reducing nitrogen loss 

from farm fields 

The nutrient management treatment level simulated in this 

study represents feasible and proven conservation practices 

that are currently being successfully applied. There are, 

however, emerging conservation technologies that have the 

potential to further reduce nutrient loss from farm fields 

and provide even greater conservation benefits once the 

technologies become more widespread. These include— 

 variable rate technology for precise nutrient application 

rates and placement methods; 

 nitrogen use efficiency enhancers (time release and 

ammonia loss inhibitors); 

 water control management that reduces late fall and early 

spring flushes of nitrate-laden drainage water; and 

 constructed wetlands receiving surface water runoff 

from farm fields prior to discharge to streams and 

rivers. 
Draft June 2010 Page 118 

New technologies that have the potential to increase crop 

yields without increasing nutrient inputs could further improve 

crop nutrient use efficiency and reduce offsite transport of 

nutrients relative to the level of crop production. 

Diminishing returns from additional conservation 

treatment. 

Tables 39 through 42 and figures 62 through 66 suggest 

diminishing returns from additional conservation treatment 

when the most vulnerable acres are treated first. These 

diminishing returns are shown explicitly in table 43, which 

includes estimates of the effects of additional conservation 

practices on the 22 million adequately treated acres in the 

UMRB. Diminishing returns to additional conservation 

treatment is demonstrated by comparing the average annual 

per-acre reductions in loss among the three groups of acres. 

For example, conservation treatment of the 8.5 million critical 

under-treated acres would reduce sediment loss an average of 

2.7 tons per acre per year on those acres. In comparison, 

additional treatment of the remaining 27.5 million undertreated acres would reduce sediment loss by 0.7 ton per acre 

per year on those acres, and treatment of the remaining 22 

million acres would reduce sediment loss by only 0.5 ton per 

acre per year on those acres, on average. 

Similarly, diminishing returns were pronounced for nitrogen 

and phosphorus loss. Total nitrogen loss would be reduced by 

an average of 39 pounds per acre per year on the 8.5 million 

critical under-treated acres, compared to a reduction of 25 

pounds per acre for the remaining 27.5 million under-treated 

acres and only 9 pounds per acre for the remaining 22 million 

acres. Total phosphorus loss would be reduced by an average 

of 4.6 pounds per acre per year on the 8.5 million critical 

under-treated acres, compared to a reduction of 1.8 pounds per 

acre for the remaining 27.5 million under-treated acres and 

only 1.3 pounds per acre for the remaining 22 million acres. 

For nitrogen loss in subsurface flow, however, diminishing 

returns are not evident until all the under-treated acres are 

treated, indicating that nitrogen leaching losses are pervasive 

throughout most of the region. Nitrogen lost with surface 

runoff would be reduced by an average of 18 pounds per acre 

per year on the 8.5 million critical under-treated acres, 

compared to a reduction of only 16 pounds per acre for the 

remaining 27.5 million under-treated acres. However, the 

reduction for treatment of the remaining 22 million acres 

averaged only 3 pounds per acre. 

Diminishing returns for reduction in environmental risk for 

pesticides were also not evident, primarily because pesticide 

risk was not taken into account in the identification of undertreated acres and the assessment of conservation treatment 

needs. 

Estimates of edge-of-field sediment and nutrient 

savings due to use of conservation practices 

A convenient way to envision the potential gains from further 

conservation treatment is to contrast the potential sediment 

and nutrient savings to estimated savings for the conservation 

practices currently in use. The no-practice scenario represents 

losses without any conservation practices, and the treatment of 

all acres with nutrient management and water erosion control 

practices was used to represent a “full-treatment” condition. 

The difference in sediment and nutrient loss between these 

two scenarios was used to represent the maximum amount of 

savings possible for conservation treatment, which totaled 176 

million tons of sediment, 876,791 tons of nitrogen, and 

142,102 tons of phosphorus for the UMRB. 

As shown in figure 69, about 70 percent of the potential 

sediment savings are accounted for by the conservation 

practices already in use, as represented by the baseline 

conservation condition. Additional treatment of the 8.5 million 

critical under-treated acres would account for another 13 

percent of the potential sediment savings. Additional treatment 

of the remaining 27.5 million under-treated acres would 

account for about 11 percent of the potential savings. 

Similar percentages were estimated for total phosphorus 

savings. About 59 percent of the potential savings are 

accounted for by the conservation practices already in use, as 

represented by the baseline conservation condition. Additional 

treatment of the 8.5 million critical under-treated acres would 

account for another 14 percent of the potential phosphorus 

savings. Additional treatment of the remaining 27.5 million 

under-treated acres would account for another 17 percent of 

the potential savings. 

Much less progress is evident for total nitrogen. The baseline 

conservation condition accounts for only 30 percent of the 

potential savings from conservation treatment. Treatment of 

the 8.5 million critical under-treated acres would account for 

an additional 19 percent of the potential nitrogen savings. 

Treatment of the remaining 27.5 million under-treated acres 

would account for another 40 percent of the potential nitrogen 

savings. 
Draft June 2010 Page 119 

Table 41. Conservation practice effects for additional treatment of 36 million under-treated acres in the Upper Mississippi River 

Basin 

Model simulated outcome 

Baseline 

conservation 

condition 

Treatment with erosion control 

practices 

Treatment with erosion control 

and nutrient management 

practices 

Average annual 

amount 

Average 

annual amount 

Percent 

reduction 

Average 

annual amount 

Percent 

reduction 

Water flow 

Surface water runoff (inches) 3.6 2.9 18% 2.9 19% 

Subsurface water flow (inches) 7.2 7.5 -6% 7.7 -7% 

Erosion and sediment loss 

Wind erosion (tons/acre) 0.2 0.2 8% 0.2 11% 

Sheet and rill erosion (tons/acre) 1.3 0.3 77% 0.3 78% 

Sediment loss at edge of field due to water 

erosion (tons/acre) 1.3 0.1 93% 0.1 93% 

Soil organic carbon 

Change in soil organic carbon, including 

loss of carbon with wind and water erosion 

(pounds/acre) 71 131 -- 124 -- 

Nitrogen 

Nitrogen applied (pounds/acre) 100.0 96.1 4%* 65.7 34% 

Nitrogen in crop yield removed at harvest 

(pounds/acre) 106.6 103.6 3%* 99.6 7% 

Total nitrogen loss for all pathways except 

harvest (pounds/acre) 49.9 41.4 17% 21.2 57% 

Loss of nitrogen with surface runoff, 

including waterborne sediment 

(pounds/acre) 10.3 2.2 78% 1.8 82% 

Nitrogen loss in subsurface flow 

(pounds/acre) 28.0 27.6 1% 11.1 60% 

Phosphorus 

Phosphorus applied (pounds/acre) 24.1 23.5 2% 18.2 24% 

Total phosphorus loss for all pathways 

except harvest (pounds/acre) 3.4 1.7 50% 1.0 71% 

Loss of phosphorus with surface 

runoff, including waterborne sediment 

(pounds/acre) 3.0 1.3 57% 0.7 78% 

Pesticide loss 

Mass loss of pesticides for all pathways 

(grams of active ingredient/hectare) 8.5 4.8 43% 4.8 43% 

Surface water pesticide risk indicator for 

aquatic ecosystem 2.5 2.4 5% 2.4 4% 

Surface water pesticide risk indicator for 

humans 0.3 0.2 27% 0.2 27% 

* Total nitrogen applied was less in the treatment scenario than in the baseline because a small fraction of the field was removed from production to 

simulate use of additional edge-of-field buffer and filtering practices. This also explains the small decrease in nitrogen in the crop yield at harvest. 

Note: Values reported in this table are for the 36 million under-treated acres only. Percent reductions are with respect to the baseline conservation 

condition. 

Note: Percent reductions were calculated prior to rounding the values for reporting in the table and the associated text. 

 
Draft June 2010 Page 120 

Table 42. Conservation practice effects for the region as a whole* after additional treatment of 36 million under-treated acres in the

Upper Mississippi River Basin 

Model simulated outcome 

Baseline 

conservation 

condition 

Treatment with erosion control 

practices 

Treatment with erosion control 

and nutrient management 

practices 

Average annual 

amount 

Average 

annual amount 

Percent 

reduction 

Average 

annual amount 

Percent 

reduction 

Water flow 

Surface water runoff (inches) 4.0 3.6 10% 3.6 11% 

Subsurface water flow (inches) 6.7 6.9 -4% 7.0 -5% 

Erosion and sediment loss 

Wind erosion (tons/acre) 0.2 0.2 5% 0.2 7% 

Sheet and rill erosion (tons/acre) 1.0 0.4 60% 0.4 61% 

Sediment loss at edge of field due to water 

erosion (tons/acre) 1.0 0.3 74% 0.3 74% 

Soil organic carbon 

Change in soil organic carbon, including 

loss of carbon with wind and water erosion 

(pounds/acre) 70 107 -- 103 -- 

Nitrogen 

Nitrogen applied (pounds/acre) 87.8 85.5 3% 66.6 24% 

Nitrogen in crop yield removed at harvest 

(pounds/acre) 107.6 105.7 2% 103.2 4% 

Total nitrogen loss for all pathways except 

harvest (pounds/acre) 41.3 36.1 13% 23.6 43% 

Loss of nitrogen with surface runoff, 

including waterborne sediment 

(pounds/acre) 8.6 3.6 58% 3.4 61% 

Nitrogen loss in subsurface flow 

(pounds/acre) 21.8 21.6 1% 11.4 48% 

Phosphorus 

Phosphorus applied (pounds/acre) 22.3 22.0 2% 18.7 16% 

Total phosphorus loss for all pathways 

except harvest (pounds/acre) 3.0 1.9 35% 1.5 51% 

Loss of phosphorus with surface 

runoff, including waterborne sediment 

(pounds/acre) 2.5 1.5 41% 1.1 57% 

Pesticide loss 

Mass loss of pesticides for all pathways 

(grams of active ingredient/hectare) 8.4 6.1 27% 6.1 27% 

Surface water pesticide risk indicator for 

aquatic ecosystem 2.6 2.5 3% 2.5 2% 

Surface water pesticide risk indicator for 

humans 0.4 0.3 14% 0.3 15% 

* Results presented for the region as a whole combine model output for the 36 million treated acres with model results from the baseline conservation 

condition for the remaining acres. 

Note: Percent reductions are with respect to the baseline conservation condition. 

Note: Percent reductions were calculated prior to rounding the values for reporting in the table and the associated text. 

 
Draft June 2010 Page 121 

Figure 62. Estimates of average annual sediment loss for under-treated acres treated with water erosion control and nutrient 

management compared to the baseline conservation condition and the no-practice scenario, Upper Mississippi River Basin 

 

0

2

4

6

8

10

12

14

16

18

20

0 10 20 30 40 50 60 70 80 90 100

Average annual sediment loss (tons/acre)

Cumulative percent acres

No-practice scenario

Baseline conservation condition

Treatment of 8.5 million critical under-treated acres

Treatment of 36 million under-treated acres
Draft June 2010 Page 122 

Figure 63. Estimates of average annual total nitrogen loss for under-treated acres treated with water erosion control and nutrient 

management compared to the baseline conservation condition and the no-practice scenario, Upper Mississippi River Basin 

 

0

20

40

60

80

100

120

140

160

180

200

0 10 20 30 40 50 60 70 80 90 100

Average annual total nitrogen loss (pounds/acre)

Cumulative percent acres

No-practice scenario

Baseline conservation condition

Treatment of 8.5 million critical under-treated acres

Treatment of 36 million under-treated acres
Draft June 2010 Page 123 

Figure 64. Estimates of average annual loss of nitrogen with surface runoff for under-treated acres treated with water erosion control 

and nutrient management compared to the baseline conservation condition and the no-practice scenario, Upper Mississippi River 

Basin 

 

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90 100

Average annual nitrogen lost with surface runoff (pounds/acre)

Cumulative percent acres

No-practice scenario

Baseline conservation condition

Treatment of 8.5 million critical under-treated acres

Treatment of 36 million under-treated acres
Draft June 2010 Page 124 

Figure 65. Estimates of average annual loss of nitrogen in subsurface flow for under-treated acres treated with water erosion control 

and nutrient management compared to the baseline conservation condition and the no-practice scenario, Upper Mississippi River 

Basin 

 

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90 100

Average annual nitrogen loss in subsurface flow (pounds/acre)

Cumulative percent acres

No-practice scenario

Baseline conservation condition

Treatment of 8.5 million critical under-treated acres

Treatment of 36 million under-treated acres
Draft June 2010 Page 125 

Figure 66. Estimates of average annual phosphorus lost with surface runoff for under-treated acres treated with water erosion control 

and nutrient management compared to the baseline conservation condition and the no-practice scenario, Upper Mississippi River 

Basin

 

0

2

4

6

8

10

12

14

16

18

20

0 10 20 30 40 50 60 70 80 90 100

Average annual phosphorus lost with surface runoff (pounds/acre)

Cumulative percent acres

No-practice scenario

Baseline conservation condition

Treatment of 8.5 million critical under-treated acres

Treatment of 36 million under-treated acres
Draft June 2010 Page 126 

Figure 67. Estimates of average annual change in soil organic carbon for under-treated acres treated with water erosion control and

nutrient management compared to the baseline conservation condition and the no-practice scenario, Upper Mississippi River Basin

 

-600

-500

-400

-300

-200

-100

0

100

200

300

400

500

600

0 10 20 30 40 50 60 70 80 90 100

Average annual change in soil organic carbon (pounds/acre)

Cumulative percent acres

No-practice scenario

Baseline conservation condition

Treatment of 8.5 million critical under-treated acres

Treatment of 36 million under-treated acres
Draft June 2010 Page 127 

Figure 68. Estimates of average annual removal of nitrogen with crop yield at harvest for under-treated acres treated with water 

erosion control and nutrient management compared to the baseline conservation condition and the no-practice scenario, Upper 

Mississippi River Basin

0

20

40

60

80

100

120

140

160

180

200

0 10 20 30 40 50 60 70 80 90 100

Removal of nitrogen with crop yield at harvest (pounds/acre)

Cumulative percent acres

No-practice scenario

Baseline conservation condition

Treatment of 8.5 million critical under-treated acres

Treatment of 36 million under-treated acres
Draft June 2010 Page 128 

Table 43 Effects of additional conservation treatment with erosion control practices and nutrient management practices for three 

groups of acres comprising the 58 million cropped acres in the Upper Mississippi River Basin 

Additional treatment for 8.5 million 

critical under-treated acres

Additional treatment for 27.5 million 

non-critical under-treated acres

Additional treatment for remaining 

22.2 million acres

Baseline Treatment scenario Baseline Treatment scenario Baseline Treatment scenario

Average 

annual 

amount 

Average 

annual 

amount Reduction 

Average 

annual 

amount 

Average 

annual 

amount Reduction 

Average 

annual 

amount 

Average 

annual 

amount Reduction 

Water flow 

Surface water runoff (inches) 3.8 3.1 0.8 3.5 2.9 0.7 4.7 3.8 0.9 

Subsurface water flow (inches) 7.7 8.2 -0.5 7.0 7.5 -0.5 5.9 6.5 -0.6 

Erosion and sediment loss 

Wind erosion (tons/acre) 0.30 0.26 0.04 0.22 0.20 0.02 0.24 0.22 0.02 

Sheet and rill erosion (tons/acre) 2.35 0.47 1.88 0.98 0.23 0.75 0.61 0.18 0.42 

Sediment loss at edge of field due to 

water erosion (tons/acre) 2.82 0.14 2.68 0.77 0.07 0.70 0.53 0.07 0.46 

Soil organic carbon 

Change in soil organic carbon, 

including loss of carbon with wind 

and water erosion (pounds/acre) -53 62 116* 109 143 35* 68 98 30* 

Nitrogen 

Nitrogen applied (pounds/acre) 107 70 37 98 64 33 68 57 11 

Nitrogen in crop yield removed at 

harvest (pounds/acre) 105 98 7 107 100 7 109 104 5 

Total nitrogen loss for all pathways 

except harvest (pounds/acre) 65 26 39 45 20 25 28 19 9 

Loss of nitrogen with surface 

runoff, including waterborne 

sediment (pounds/acre) 20.0 2.7 17.3 7.3 1.5 5.7 5.8 1.7 4.1 

Nitrogen loss in subsurface flow 

(pounds/acre) 31.8 13.6 18.1 26.8 10.4 16.5 11.8 8.8 3.0 

Phosphorus 

Phosphorus applied (pounds/acre) 26.9 19.3 7.5 23.2 17.8 5.4 19.5 17.0 2.5 

Total phosphorus loss for all pathways 

except harvest (pounds/acre) 5.9 1.4 4.6 2.7 0.9 1.8 2.2 1.0 1.3 

Loss of phosphorus with surface 

runoff, including waterborne 

sediment (pounds/acre) 5.4 1.0 4.4 2.3 0.6 1.7 1.8 0.6 1.2 

Pesticide loss 

Mass loss of pesticides for all 

pathways (grams of active 

ingredient/hectare) 12.7 5.7 7.0 7.2 4.6 2.6 8.2 5.0 3.2 

Surface water pesticide risk indicator 

for aquatic ecosystem 2.4 1.7 0.7 2.6 2.7 -0.1 2.7 1.8 0.9 

Surface water pesticide risk indicator 

for humans 0.5 0.3 0.1 0.3 0.2 0.1 0.5 0.3 0.2 

* Gain in soil organic carbon. 

 
Draft June 2010 Page 129 

Figure 69. Comparison of estimated sediment, nitrogen, and phosphorus savings that are due to practices in use in the baseline 

conservation condition and potential savings with additional water erosion control and nutrient management treatment of cropped 

acres in the Upper Mississippi River Basin 

Tons of sediment, nitrogen, and phosphorus saved or potentially saved due to conservation practices 

Estimated savings due 

to conservation practice 

use (baseline 

conservation condition) 

Potential savings 

from treatment of 8.5 

million critical undertreated acres* 

Potential savings 

from treatment of 

27.5 million noncritical undertreated acres* 

Potential 

savings from 

treatment of 

remaining 

22.2 million 

acres* 

Total estimated and 

potential savings 

from conservation 

treatment 

Sediment 124,048,565 22,664,266 19,240,443 10,191,405 176,144,679 

Nitrogen 264,923 164,662 350,548 96,658 876,791 

Phosphorus 84,074 19,252 24,829 13,947 142,102 

*Treatment with erosion control practices and nutrient management practices on all acres. 

 Note: Calculations exclude land in long-term conserving cover. 

70

30

59

13

19

14

11

40

17

6 11 10

0

10

20

30

40

50

60

70

80

90

100

Sediment loss Total nitrogen loss Total phosphorus loss

Percent of total estimated and potential savings from 

conservation treatment

Baseline conservation condition

Treatment of 8.5 million critical under-treated acres

Treatment of 27.5 million additional under-treated acres

Treatment of remaining 22.2 million acres
Draft June 2010 Page 130 

Potential for Offsite Water Quality Gains 

The field-level model results for the scenarios with additional 

erosion control practices and nutrient management was used 

with the HUMUS/SWAT model to determine the potential for 

further reductions in instream sediment and nutrient loads with 

additional conservation treatment. 

Percent reductions relative to the current conservation 

condition were estimated for each of two scenarios: (1) 

treatment of the 8.5 million critical under-treated acres, and 

(2) treatment of all 36 million under-treated acres, including 

the 8.5 million critical under-treated acres (tables 44 through 

47). The distribution of under-treated acres within the UMRB 

is shown in chapter 6, table 35. The model simulations not 

only demonstrate the relative gains that can be expected from 

different levels of conservation effort but also provide insight 

into which subbasins are the most important in terms of 

reducing overall loads exported from the UMRB. Figures 70 

through 73 compare the baseline condition with the estimates 

of reductions achievable under the two scenarios. 

Summary of results for the entire basin 

Model simulations show that at the outlet of the UMRB 

(Grafton, IL), treatment of the 8.5 million critical undertreated acres with additional erosion control and nutrient 

management practices would further reduce instream loads, 

relative to the baseline conservation condition, by— 

 10 percent for sediment; 

 12 percent for nitrogen; 

 14 percent for phosphorus; and 

 7 percent for atrazine. 

Treatment of all 36 million under-treated acres would reduce 

instream loads at the outlet of the UMRB (Grafton, IL), 

relative to the baseline conservation condition, by— 

 19 percent for sediment; 

 39 percent for nitrogen; 

 37 percent for phosphorus; and 

 20 percent for atrazine. 

Summary of results for the 14 subbasins 

The subbasins with the highest percent reductions due to 

additional conservation treatment of the 8.5 million critical 

under-treated acres would be: 

 for sediment, the Rock River (subbasin code 0709) with a 

22-percent reduction in load; 

 for nitrogen, the Wisconsin River (subbasin code 0707) 

with a 20 percent reduction in load and the Chippewa 

River (subbasin code 0705), with a 23 percent reduction; 

 for phosphorus, the Wisconsin River (subbasin code 

0707) and the Chippewa River (subbasin code 0705), both 

with 29 percent reductions in loads; and 

 for atrazine, the Chippewa River (subbasin code 0705) 

with a 35-percent reduction. 

A similar set of subbasins had the highest percent reductions 

due to additional treatment of all 36 million under-treated 

acres. Subbasins with the highest percent load reductions 

would be: 

 for sediment, the Rock River (subbasin code 0709) with a 

45-percent reduction in load; 

 for nitrogen, the Minnesota River (subbasin code 0702) 

with a 49-percent reduction in load; 

 for phosphorus, the Wisconsin River (subbasin code 

0707) with a 51-percent reduction in load; and 

 for atrazine, the Chippewa River (subbasin code 0703) 

with a 39-percent reduction. 

Agricultural sources are relatively minor in two subbasins, the 

St. Croix River (subbasin code 0703) and the Upper Illinois 

River (subbasin code 0712), which explains the low percent 

reduction in instream loads due to additional conservation 

practices in those subbasins. 
Draft June 2010 Page 131 

Table 44. Effects of additional conservation treatment with erosion control practices and nutrient management practices on instream 

sediment loads, Upper Mississippi River Basin 

 

Baseline 

conservation 

condition 

Treatment of 8.5 million critical 

under-treated acres

Treatment of all 36 million undertreated acres

Subbasin 

code Subbasin name 

Average 

annual load 

(1,000 tons) 

Average 

annual load 

(1,000 tons) 

Percent 

reduction

Average 

annual load 

(1,000 tons) 

Percent 

reduction

Tributary subbasins 

0702 Minnesota River 873 802 8 708 19 

0703 St. Croix River 520 509 2 505 3 

0705 Chippawa River 962 750 22 697 28 

0707 Wisconsin River 1,120 961 14 933 17 

0708a Iowa River within 708 1,630 1,450 11 1,190 27 

0709 Rock River 1,530 1,190 22 849 45 

0710 Des Moines River 792 743 6 673 15 

0713 Illinois River 6,380 6,150 4 5,410 15 

0712 Upper Illinois River within 713 1,960 1,930 1 1,830 7 

Outlets along mainstem 

0701 Mississippi Headwaters 2,620 2,420 8 2,160 17 

0704 Upper Mississippi-Black-Root 5,980 4,960 17 4,450 26 

0706 Upper Mississippi-Maquoketa-Plum 9,040 7,550 16 6,750 25 

0708 Upper Mississippi-Iowa-SkunkWapsipinicon 15,600 13,500 14 11,800 25 

0711 Mississippi at Grafton, Illinois 20,900 18,700 10 16,800 19 

Note: Percent reductions were calculated prior to rounding the values for reporting in the table and the associated text. 

 

Table 45. Effects of additional conservation treatment with erosion control practices and nutrient management practices on instream 

nitrogen loads, Upper Mississippi River Basin 

 

Baseline 

conservation 

condition 

Treatment of 8.5 million critical 

under-treated acres

Treatment of all 36 million 

under-treated acres

Subbasin 

code Subbasin name 

Average 

annual load 

(1,000 pounds) 

Average 

annual load 

(1,000 pounds) 

Percent 

reduction

Average 

annual load 

(1,000 pounds) 

Percent 

reduction

Tributary subbasins 

0702 Minnesota River 108,000 97,700 9 54,900 49 

0703 St. Croix River 13,600 13,500 1 13,200 3 

0705 Chippawa River 23,500 18,200 23 15,200 35 

0707 Wisconsin River 43,400 34,800 20 30,000 31 

0708a Iowa River within 708 117,000 107,000 9 72,000 39 

0709 Rock River 94,200 80,300 15 56,400 40 

0710 Des Moines River 117,000 113,000 3 74,900 36 

0713 Illinois River 424,000 404,000 5 304,000 28 

0712 Upper Illinois River within 713 166,000 155,000 6 140,000 16 

Outlets along mainstem 

0701 Mississippi Headwaters 185,000 168,000 9 112,000 39 

0704 Upper Mississippi-Black-Root 304,000 263,000 13 189,000 38 

0706 Upper Mississippi-Maquoketa-Plum 409,000 350,000 15 252,000 38 

0708 

 Upper Mississippi-Iowa-SkunkWapsipinicon 764,000 658,000 14 455,000 40 

0711 Mississippi at Grafton, Illinois 1,090,000 959,000 12 666,000 39 

Note: Percent reductions were calculated prior to rounding the values for reporting in the table and the associated text. 

 
Draft June 2010 Page 132 

Table 46. Effects of additional conservation treatment with erosion control practices and nutrient management practices on instream 

phosphorus loads, Upper Mississippi River Basin 

 

Baseline 

conservation 

condition 

Treatment of 8.5 million critical 

under-treated acres

Treatment of all 36 million 

under-treated acres

Subbasin 

code Subbasin name 

Average 

annual load 

(1,000 pounds) 

Average 

annual load 

(1,000 pounds) 

Percent 

reduction

Average 

annual load 

(1,000 pounds) 

Percent 

reduction

Tributary subbasins 

0702 Minnesota River 3,340 3,020 10 2,090 38 

0703 St. Croix River 521 457 12 454 13 

0705 Chippawa River 1,610 1,140 29 845 47 

0707 Wisconsin River 2,830 2,020 29 1,400 51 

0708a Iowa River within 708 6,000 5,140 14 3,710 38 

0709 Rock River 6,060 4,610 24 3,240 47 

0710 Des Moines River 3,540 3,380 5 2,490 30 

0713 Illinois River 24,100 23,500 3 20,100 17 

0712 Upper Illinois River within 713 10,800 10,700 1 10,300 5 

Outlets along mainstem 

0701 Mississippi Headwaters 7,250 6,220 14 4,980 31 

0704 Upper Mississippi-Black-Root 12,700 10,000 21 7,810 38 

0706 Upper Mississippi-Maquoketa-Plum 19,000 15,000 21 10,200 46 

0708 Upper Mississippi-Iowa-SkunkWapsipinicon 35,200 28,600 19 20,100 43 

0711 Mississippi at Grafton, Illinois 45,200 38,700 14 28,500 37 

Note: Percent reductions were calculated prior to rounding the values for reporting in the table and the associated text. 

Table 47. Effects of additional conservation treatment with erosion control practices and nutrient management practices on instream 

atrazine loads, Upper Mississippi River Basin 

 

Baseline 

conservation 

condition 

Treatment of 8.5 million critical 

under-treated acres

Treatment of all 36 million 

under-treated acres

Subbasin 

code Subbasin name 

Average 

annual load 

(pounds) 

Average 

annual load 

(pounds) 

Percent 

reduction

Average 

annual load 

(pounds) 

Percent 

reduction

Tributary subbasins 

0702 Minnesota River 3,052 2,954 3 2,582 15 

0703 St. Croix River 128 122 5 108 16 

0705 Chippawa River 854 555 35 517 39 

0707 Wisconsin River 1,146 1,082 6 930 19 

0708a Iowa River within 708 9,614 9,071 6 7,389 23 

0709 Rock River 4,915 4,450 9 3,745 24 

0710 Des Moines River 3,800 3,629 4 3,326 12 

0713 Illinois River 17,297 17,089 1 15,500 10 

0712 Upper Illinois River within 713 7,144 7,161 0 6,787 5 

Outlets along mainstem 

0701 Mississippi Headwaters 5,470 5,103 7 4,520 17 

0704 Upper Mississippi-Black-Root 7,901 7,130 10 6,094 23 

0706 Upper Mississippi-Maquoketa-Plum 6,315 5,864 7 4,905 22 

0708 Upper Mississippi-Iowa-SkunkWapsipinicon 33,335 30,791 8 26,140 22 

0711 Mississippi at Grafton, Illinois 47,826 44,349 7 38,206 20 

Note: Percent reductions were calculated prior to rounding the values for reporting in the table and the associated text. 

 
Draft June 2010 Page 133 

Figure 70. Estimates of average annual instream sediment loads for the baseline conservation condition compared to two scenarios 

simulating additional water erosion control and nutrient management practices for subbasins in the Upper Mississippi River Basin 

Note: Loadings from all sources other than cultivated cropland are labeled “background” in the figure; for this scenario, cultivated cropland was simulated using a 

continuous grass cover without any tillage or addition of nutrients or pesticides and no harvest.
Draft June 2010 Page 134 

Figure 71. Estimates of average annual instream nitrogen loads for the baseline conservation condition compared to two scenarios 

simulating additional water erosion control and nutrient management practices for subbasins in the Upper Mississippi River Basin 

Note: Loadings from all sources other than cultivated cropland are labeled “background” in the figure; for this scenario, cultivated cropland was simulated using a 

continuous grass cover without any tillage or addition of nutrients or pesticides and no harvest.
Draft June 2010 Page 135 

Figure 72. Estimates of average annual instream phosphorus loads for the baseline conservation condition compared to two scenarios 

simulating additional water erosion control and nutrient management practices for subbasins in the Upper Mississippi River Basin 

Note: Loadings from all sources other than cultivated cropland are labeled “background” in the figure; for this scenario, cultivated cropland was simulated using a 

continuous grass cover without any tillage or addition of nutrients or pesticides and no harvest.
Draft June 2010 Page 136 

Figure 73. Estimates of average annual instream atrazine loads for the baseline conservation condition compared to two scenarios 

simulating additional water erosion control and nutrient management practices for subbasins in the Upper Mississippi River Basin 
Draft June 2010 Page 137 

References 

Arnold, J.G., R. Srinivasan, R.S. Muttiah, and J.R. Williams. 1998. Large area hydrologic modeling and assessment part I: model development. 

Journal of the American Water Resources Association. 34(1): 73-89. 

Arnold, J.G., R. Srinivasan, R.S. Muttiah, and P.M. Allen. 1999. Continental scale simulation of the hydrologic balance. Journal of the American 

Water Resources Association. 35(5): 1037-1052. 

Arnold, J.G. and N. Fohrer. 2005. SWAT2000: current capabilities and research opportunities in applied watershed modeling. Hydrological 

Processes. 19(3): 563-572. 

Coble, H. “Measuring the Resilience of IPM Systems—The PAMS Diversity Index.” Unpublished manuscript. U.S. Department of Agriculture. 

1998. 

Duriancik, L.F., D. Bucks, J.P. Dobrowolski, T. Drewes, S.D. Eckles, L. Jolley, R.L. Kellogg, D. Lund, J.R. Makuch, M.P. O’Neill, C.A. Rewa, 

M.R. Walbridge, R. Parry, and M. Weltz. 2008. The first five years of the Conservation Effects Assessment Project. Journal of Soil and Water 

Conservation, Nov.-Dec. 2008. 

Eischeid, Jon K., Phil A. Pasteris; Henry F. Diaz, Marc S. PLantico, and Neal J. Lott. 2000. Creating a serially complete, national 

daily time series of temperature and precipitation for the western United States.” Journal of Applied Meteorology 39 

(September):1580-1591. 

Gassman, Philip W., Jimmy R. Williams, Verel W. Benson, R. Cesar Izaurralde, Larry Hauck, C. Allan Jones, Jay D. Atwood, James Kiniry, and 

Joan D. Flowers. 2005. Historical Development and Applications of the EPIC and APEX Models. Working Paper 05-WP 397, Center for

Agricultural and Rural Development, Iowa State University, Ames, IA. 

Gassman, P.W., M.R. Reyes, C.H. Green, and J.G. Arnold. 2007. The Soil and Water Assessment Tool: Historical development, applications and 

future research directions. Transactions of the American Society of Agricultural and Biological Engineers 50(4): 1211-1250. 

Gassman, P.W., J.R. Williams, S. Wang, A. Saleh, E. Osei, L. Hauck, C. Izaurralde, and J. Flowers. 2009. The Agricultural Policy Environmental 

Extender (APEX) model: An emerging tool for landscape and watershed environmental analyses. Technical Report 09-TR 49. CARD, Iowa 

State Univ., Ames, IA. Available at: http://www.card.iastate.edu/publications/synopsis.aspx?id=1101. 

Gassman, P.W., J.R. Williams, S. Wang, A. Saleh, E. Osei, L. Hauck, C. Izaurralde, and J. Flowers. 2010. The Agricultural Policy Environmental 

Extender (APEX) model: An emerging tool for landscape and watershed environmental analyses. Trans. of the ASABE (forthcoming). 

Goebel, J.J., and H.D. Baker. 1987. The 1982 National Resources Inventory Sample Design and Estimation Procedures. Statistical Laboratory, Iowa 

State University, Ames, IA. 

Goebel, J.J. 1998. The National Resources Inventory and its role in U.S. agriculture. In Agricultural Statistics 2000. International Statistical Institute, 

Voorburg, The Netherlands, 181–192. 

Goebel, J.J., and R.L. Kellogg. 2002. Using survey data and modeling to assist the development of agri-environmental policy. In Conference on 

Agricultural and Environmental Statistical Applications in Rome. National Statistical Institute of Italy, Rome, Italy, 695–705.

Goss, Don W., Robert L. Kellogg, Joaquin Sanabria, Susan Wallace, and Walt Kniesel. 1998. The National Pesticide Loss Database: A Tool for 

Management of Large Watersheds. Poster presentation at the 53rd annual Soil and Water Conservation Society conference. San Diego, CA, July 

5–9., 1998. 

Izaurralde, R. C., J. R. Williams, W. B. McGill, N. J. Rosenberg, M. C. Quiroga Jakas. 2006. Simulating soil C dynamics with EPIC: Model 

description and testing against long-term data. Ecol. Model. 192: 362–384. 

Kellogg, R.L., M.S. Maizel, and D.W. Goss. 1992. Agricultural Chemical Use and Ground Water Quality: Where Are the Problem Areas? U.S. 

Department of Agriculture, Soil Conservation Service. 

Kellogg, Robert L., Margaret Maizel, and Don W. Goss. 1994. The potential for leaching of agrichemicals used in crop production: A national 

perspective. Journal of Soil and Water Conservation 49(3):294–298. 

Kellogg, Robert L., Don W. Goss, Susan Wallace, and Klaus Alt. 1997. Potential Priority Watersheds for Protection of Water Quality from NonPoint Sources Related to Agriculture. Poster Presentation at the 52nd Annual Soil and Water Conservation Society Conference. Toronto, Ontario, 

Canada. July 22–25, 1997. 

Kellogg. Robert L. 2000. Potential Priority Watersheds for Protection of Water Quality from Contamination by Manure Nutrients. Presented at the 

Water Environment Federation’s Animal Residuals Management Conference 2000. Kansas City, MO. November 12–14, 2000. 

Kellogg, Robert L. Richard F. Nehring, Arthur Grube, Donald W. Goss, and Steven Plotkin. 2002. Environmental indicators of pesticide leaching 

and runoff from farm fields. In Ball, V. Eldon, and George W. Norton (editors), Agricultural Productivity: Measurement and Sources of Growth. 

Kluwer Academic Publishers, Boston, MA. 

Maresch, W., M.R. Walbridge, and D. Kugler. 2008. Enhancing conservation on agricultural landscapes: A new direction for the Conservation 

Effects Assessment Project. Journal of Soil and Water Conservation, Nov.-Dec. 2008. 
Draft June 2010 Page 138 

Mausbach, M.J., and A.R. Dedrick. 2004. The length we go: Measuring environmental effects of conservation practices. Journal of Soil and Water 

Conservation, Sept.-Oct. 2004. 

Nusser, S.M., and J.J. Goebel. 1997. The National Resources Inventory: A long-term multi-resource monitoring programme. Environmental and 

Ecological Statistics 4:181–204. 

Potter, S.R., S. Andrews, J.D. Atwood, R.L. Kellogg, J. Lemunyon, L. Norfleet, and D. Oman. 2006. Model simulation of soil loss, nutrient loss, and 

change in soil organic carbon associated with crop production. USDA, Natural Resources Conservation Service, Washington, DC. Available at 

http://www.nrcs.usda.gov/technical/nri/ceap/croplandreport/ (verified 8 June 2008). 

Srinivasan, R.S., J.G. Arnold, and C.A. Jones. 1998. Hydrologic modeling of the United States with the Soil and Water Assessment Tool. 

International Journal of Water Resources Development. 14(3): 315-325. 

U.S. Department of Agriculture, Natural Resources Conservation Service. 1989. The Second RCA Appraisal, Analysis of Conditions and Trends. 

280 pages. 

U.S. Department of Agriculture, Natural Resources Conservation Service. 2002. 1997 National Resources Inventory Summary Report. Washington, 

DC. Available at http://www.nrcs.usda.gov/technical/nri/1997/summry_report/index.html. 

United States Department of Agriculture, Natural Resources Conservation Service. 2003. Costs Associated With Development and Implementation 

of Comprehensive Nutrient Management Plans. 

United States Department of Agriculture, Natural Resources Conservation Service. 2007. 2003 National Resources Inventory. 

http://www.nrcs.usda.gov/NRI. United States Department of Agriculture, National Agricultural Statistics Service. 2009. 2007 Census of 

Agriculture. Database. 

U.S. Environmental Protection Agency. 2007. 2001 National Land Cover Data (NLCD 2001). Available at http://epa.gov/mrlc/nlcd-2001.html. 

USDA-Farm Service Agency. June 2004. Conservation Reserve Program Overview. CRP: Planting for the Future. U.S. Department of Agriculture, 

Farm Service Agency. Washington, DC. 

U.S. Geological Survey. 1980. Hydrologic Unit Map of the United States. U.S. Department of the Interior. Washington, DC. 

Wiebe, Keith, and Noel Gollehon, editors. July 2006. Agricultural Resources and Environmental Indicators, 2006 Edition. Chapter 5, Conservation 

and Environmental Policies—USDA Land Retirement Programs. Economic Information Bulletin Number 16. U.S. Department of Agriculture, 

Economic Research Service. Washington, DC.

Williams, J. R. 1990. The erosion productivity impact calculator (EPIC) model: A case history. Phil. Trans. R. Soc. Lond. 329: 421-428. 

Williams, J. R., C. A. Jones, and P. T. Dyke. 1984. A modeling approach to determining the relationship between erosion and soil productivity. 

Trans. ASAE 27(1): 129-144. 

Williams, J. R., W. L. Harman, M. Magre, U. Kizil, J. A. Lindley, G. Padmanabhan, and E. Wang. 2006. APEX feedlot water quality simulation. 

Trans. ASAE 49(1): 61-73. 

Williams, J. R., R. C. Izaurralde, and E. M. Steglich. 2008. Agricultural Policy/Environmental eXtender Model: Theoretical documentation version 

0604. BREC Report # 2008-17. Temple, TX: Texas AgriLIFE Research, Texas A&M University, Blackland Research and Extension Center. 

Available at: http://epicapex.brc.tamus.edu/downloads/user-manuals.aspx. Accessed 31 January 2010. 

Izaurralde, R. C., J. R. Williams, W. B. McGill, N. J. Rosenberg, M. C. Quiroga Jakas. 2006. Simulating soil C dynamics with EPIC: Model 

description and testing against long-term data. Ecol. Model. 192: 362–384. 

 
Draft June 2010 Page 139 

Appendix A: Estimates of acres and 

standard errors 

This appendix will consist of a table reporting estimated acres 

and the standard error for a collection of key variables included 

in the report. 

 
Draft June 2010 Page 140 

Appendix B 

Summary Tables of NRI-CEAP 

Cropland Survey Responses 

for the Upper Mississippi River Basin 

The NRI-CEAP Cropland Survey obtained information from 

farmers on field-level farming activities and conservation 

practices for a subset of National Resource Inventory (NRI) 

cultivated cropland sample points. The survey was specifically 

designed to obtain information needed as data inputs to the 

APEX physical process model. 

The NRI-CEAP Cropland Survey collected information for all 

crops and for multiple years, thereby providing a landscape 

representation of the cropping systems present. A cropping 

system represents a suite of crops typically grown in a crop 

rotation along with the field operations and chemical use 

associated with that suite of crops. 

Because of annual financial constraints as well as the logistics of 

data collection, the data collection process was spread over the 

4-year period 2003 through 2006. In each year, a separate set of 

sample points was selected. The final CEAP sample was 

constructed by pooling the set of usable, completed surveys from 

all 4 years. The results therefore represent farming activities 

from 2003 through 2006. 

Survey questionnaire responses are summarized in this appendix 

for the 3,703 CEAP samples in the Upper Mississippi River 

Basin (UMRB). These results reflect what was reported in the 

survey and do not include adjustments that were necessary to 

conduct the physical process modeling.24 Because the samples 

were drawn from an area sample frame, all data summaries are 

in terms of acres.25

Survey Data Collection 

The National Agricultural Statistics Service (NASS) 

administered the survey with assistance from FSA and NRCS. 

NASS, the agency that has the authority to conduct public 

surveys for USDA, has the staff, infrastructure, and experience 

to implement large survey efforts of this nature. The survey was 

conducted in two phases. 

Phase I 

The names and addresses of the operators of the fields associated 

with the sample point locations were obtained in Phase I. The 

collection of the name and address information provided (1) a 

contact for providing the operator with survey publicity 

materials encouraging cooperation, and (2) an initial contact for 

field enumeration to begin the second phase. 

 

24 See the documentation report “Transforming Survey Data to APEX Model 

Input Files” at http://www.nrcs.usda.gov/technical/nri/ceap/umrbdocumentation/. 25 An area sample frame was used so that the results would represent conditions 

on the landscape. Representation of results in terms of enterprises or farms, 

rather than acres, is incompatible with the area sample frame. 

Prior to data collection, NRCS provided NASS field 

enumerators with aerial photographs and county maps showing 

the locations of the CEAP sample sites. NRCS combined NRI 

digital location information with digital county base map 

products to plot CEAP sample point locations. County maps 

include roads, towns, hydrographic features, and other 

information for locating the general vicinity of the sample point. 

To identify the field associated with the CEAP sample point, an 

ortho-rectified (scale accurate) aerial photograph was provided 

showing the location of the sample point. 

Phase I data collection occurred in June and July. In 2003 and 

2004, NASS enumerators visited Farm Service Agency (FSA) 

field offices and, using the county maps and aerial photographs 

provided by NRCS, worked with FSA staff to determine the 

identity of the farm operator. Once the point had been visibly 

located on FSA photography, the FSA farm field and tract 

number information were extracted and recorded. FSA databases 

were then accessed to provide the name and contact information 

for the farm operator, as well as information on Conservation 

Reserve Program (CRP) signups. For sample points that fell on 

farming operations that did not participate in USDA programs, 

county plat maps or other types of county records were 

consulted to determine the farm operator. 

In 2005 and 2006, an alternative technology and approach was 

used to identify farm operators. This approach used the digitized 

data on field boundaries referred to as the Common Land Unit 

(CLU), or FSA CLU data layer, which allowed many of the farm 

operator names and much of the contact information to be 

obtained through a digital merge process. In this process, NRI 

digital point location information was merged with CLU data to 

determine the FSA field and tract number. The field and tract 

number was then used to extract the name of the farm operator 

and other pertinent program information from FSA databases. 

Prospective respondents received an advance letter and 

information brochure informing them that they had been selected 

and that a NASS enumerator would be contacting them to ask 

about their operation of a selected field. The brochure explained 

the purpose of the survey and encouraged participation. 

Phase II 

The CEAP questionnaire was designed to be enumerated as a 

personal interview with the operator who made the day-to-day 

operating decisions. Participation in the survey was voluntary, 

and all data collected are confidential. In addition to the personal 

interview, NASS enumerators visited the NRCS field offices to 

obtain additional information about conservation program 

participation and the content of conservation plans. Data 

collection was conducted typically from September through 

December. Following data collection, NASS assembled the 

survey responses into a database. Edit checks were conducted to 

identify questionable survey responses and, where necessary, to 

follow up with the respondent to clear up discrepancies. 

Prior to the start of the fall data collection, State survey 

administrators conducted workshops at the local level to 

familiarize field enumerators with the questionnaire, techniques 

for obtaining successful interviews, and educating enumerators 
Draft June 2010 Page 141 

on common practices found in their State. The State workshops 

ranged from 1.5 to 2.5 days. Training methods included sectionby-section review of the questionnaire and identification of data 

relationships between sections. 

An established protocol for enumerating, handling, and editing 

questionnaires was enacted once data collection began. At the 

start of data collection, field enumerators located and 

interviewed the respondents. If the initial contact was not the 

day-to-day decision maker, enumerators identified and located 

the correct respondent and conducted the interview. If three 

attempts to locate the respondent during the survey data 

collection period failed, the enumerator coded the questionnaire 

as “inaccessible.” 

Because participation in the CEAP Survey was voluntary, 

respondents had the option to decline the interview. Some 

respondents cooperated reluctantly and although they provided 

responses to some questions, declined to complete sections of 

the questionnaire that required more detailed information 

Incomplete surveys were not used for simulation modeling. 

When beginning the interview, a screening process was used to 

determine if the NRI-CEAP point met the required definition of 

cultivated cropland. If a crop was planted or cropped for 

production, or if the cropland was idled, in summer fallow, or 

pasture in rotation with crops, the sample was considered usable 

for survey purposes and the entire questionnaire was 

enumerated. If the sample did not meet these criteria, the 

interview was concluded and the sample points were considered 

to be out-of-scope. 

--29 tables summarizing results from the survey will follow. 
Draft June 2010 Page 142 

Appendix C: Model simulation results 

on the baseline conservation condition 

for the 14 subbasins 

Model simulation results presented in Chapter 4 for the baseline 

conservation condition are presented in tables C-1 and C-2 for 

the 14 subbasins in the UMRB. The column headings refer to the 

subbasin code. The names of the subbasins are shown below: 

Sub-basin 

code Subbasin name 

0701 Mississippi Headwaters 

0702 Minnesota River Basin 

0703 St. Croix River Basin 

0704 Upper Mississippi-Black-Root 

0705 Chippewa River Basin 

0706 Upper Mississippi-Maquoketa-Plum 

0707 Wisconsin River Basin 

0708 Upper Mississippi-Iowa-Skunk-Wapsipinicon 

0709 Rock River Basin 

0710 Des Moines River Basin 

0711 Upper Mississippi-Salt 

0712 Upper Illinois River Basin 

0713 Lower Illinois River Basin 

0714 Upper Mississippi-Kaskaskia-Meramec 
Draft June 2010 

Table C-1. Average annual estimates of water flow, erosion, and soil organic carbon for the baseline conservation condition for each of the 14 sRiver Basin. Model simulated outcome UMRB 0701 0702 0703 0704 Cropped acres (million acres) 58,153,500 2,672,400 7,343,800 505,800 2,704,200 87

Percent of acres in UMRB 100 4.6% 12.6% 0.9% 4.7% 

Percent of acres irrigated 2.5 14.1% 0.2% 1.6% 1.5% 

Water sources (average annual inches) 

Non-irrigated acres 

Precipitation 33.6 28.0 27.4 31.0 32.2 

Irrigated acres 

Precipitation 33.1 27.1 25.5 31.3 31.0 

Irrigation water applied 9.3 6.7 11.6 4.9 11.1 

Water loss pathways (average annual inches) 

Evapotranspiration 23.4 20.1 22.0 20.5 22.5 

Surface water runoff 4.0 3.2 2.5 3.4 4.0 

Subsurface water flow 6.7 5.7 2.8 7.6 5.8 

Erosion and sediment loss (average annual tons/acre) 

Wind erosion 0.24 0.68 0.62 0.42 0.17 

Sheet and rill erosion 1.04 0.85 0.59 1.37 1.24 Sediment loss at edge of field due to water erosion 0.98 0.80 0.36 1.60 1.63 

Soil organic carbon (average annual pounds/acre) 

Loss of soil organic carbon with wind and water erosion 189 136 150 206 252 

Change in soil organic carbon, including loss of carbon with wind and water erosion 70 -95 10 -70 26 
Draft June 2010 

Table C-1.—continued Model simulated outcome 0708 0709 0710 0711 0712 Cropped acres (million acres) 10,383,100 4,206,000 6,309,500 2,780,300 3,989,500 8,34

Percent of acres in UMRB 17.9% 7.2% 10.8% 4.8% 6.9% 1Percent of acres irrigated 1.6% 2.0% 1.1% 1.4% 5.4% 

Water sources (average annual inches) 

Non-irrigated acres 

Precipitation 34.3 34.1 31.8 37.5 36.2 

Irrigated acres 

Precipitation 35.1 34.7 30.1 37.9 37.8 Irrigation water applied 9.6 10.1 14.0 15.2 10.1 

Water loss pathways (average annual inches) 

Evapotranspiration 23.5 23.1 23.0 24.8 23.7 Surface water runoff 4.4 4.4 3.6 5.8 4.4 

Subsurface water flow 6.6 6.7 5.2 8.0 9.3 

Erosion and sediment loss (average annual tons/acre) 

Wind erosion 0.21 0.09 0.37 0.09 0.10 Sheet and rill erosion 1.24 1.55 0.81 1.59 0.84 

Sediment loss at edge of field due to water erosion 1.16 1.70 0.59 1.46 0.77 

Soil organic carbon (average annual pounds/acre) 

Loss of soil organic carbon with wind and water erosion 230 240 176 241 148 Change in soil organic carbon, including loss of carbon with wind and water erosion 104 54 104 51 55 
Draft June 2010 

Table C-2. Average annual estimates of nitrogen loss, phosphorus loss, and pesticide loss for the baseline conservation condition for each of the Mississippi River Basin Model simulated outcome UMRB 0701 0702 0703 0704 Cropped acres (million acres) 58,153,500 2,672,400 7,343,800 505,800 2,704,200 87

Percent of acres in UMRB 100% 4.6% 12.6% 0.9% 4.7% Percent of acres with manure applied 16.3% 33.4% 16.8% 47.5% 27.7% 6

Nitrogen (average annual pounds/acre) 

Nitrogen sources 

Atmospheric deposition 6.0 4.8 5.4 4.9 5.8 Bio-fixation by legumes 57.9 37.0 46.4 49.4 50.1 Nitrogen applied as commercial fertilizer and manure 87.8 85.8 77.7 89.3 95.9 All nitrogen sources 151.7 127.5 129.5 143.7 151.9 

Nitrogen loss pathways 

 Nitrogen in crop yield removed at harvest 107.6 95.7 96.4 89.4 102.8  Nitrogen loss by volatilization 6.7 5.3 7.0 7.2 7.7  Nitrogen loss through denitrification processes 2.2 1.2 1.5 1.1 2.1  Nitrogen lost with windborne sediment 2.1 3.1 5.5 2.9 1.5 

 Nitrogen loss with surface runoff , including waterborne sediment 8.6 6.7 4.1 11.2 14.2 

 Nitrogen loss in subsurface flow pathways 21.8 25.8 16.3 39.3 25.1  Total nitrogen loss for all pathways except harvest 41.3 42.1 34.3 61.7 50.6  Change in soil nitrogen 1.8 -11.1 -2.2 -8.4 -2.7 

Phosphorus (average annual pounds/acre) 

Phosphorus applied as commercial fertilizer and manure 22.3 21.3 20.9 25.5 23.9 Phosphorus loss pathways 

Phosphorus in crop yield removed at harvest 17.0 15.4 15.0 12.3 15.8 Phosphorus lost with windborne sediment 0.4 0.8 1.0 0.8 0.3 Phosphorus lost with surface runoff, including waterborne sediment and soluble phosphorus in surface water runoff and lateral flow into 

drainage ditches 2.5 2.5 1.2 3.5 3.3 Soluble phosphorus loss to groundwater 0.0 0.0 0.0 0.0 0.0 Total phosphorus loss for all pathways except harvest 3.0 3.3 2.2 4.4 3.6 Change in soil phosphorus 2.2 2.7 3.7 8.8 4.2 

Pesticides 

Average annual amount of pesticides applied (grams of active ingredient/hectare) 1,650 1,054 1,279 835 1,281 Pesticide loss 

Average annual mass loss of pesticides for all pathways (grams of active ingredient/hectare) 8.4 4.4 2.5 7.5 6.8 Edge-of-field pesticide risk indicator 

Average annual surface water pesticide risk indicator for aquatic ecosystem 2.6 12.7 1.1 0.6 1.0 Average annual surface water pesticide risk indicator for humans 0.4 0.4 0.2 0.2 0.2 

Average annual groundwater pesticide risk indicator for humans 0.2 0.0 0.0 0.0 0.0 
Draft June 2010 

Table C-2. –continued Model simulated outcome 0708 0709 0710 0711 0712 Cropped acres (million acres) 10,383,100 4,206,000 6,309,500 2,780,300 3,989,500 8,34

Percent of acres in UMRB 17.9% 7.2% 10.8% 4.8% 6.9% 1Percent of acres with manure applied 15.1% 16.6% 14.0% 9.3% 6.9% 

Nitrogen (average annual pounds/acre) 

Nitrogen sources 

Atmospheric deposition 6.2 6.2 6.1 6.0 6.6 Bio-fixation by legumes 61.8 53.2 64.4 71.7 54.9 Nitrogen applied as commercial fertilizer and manure 90.1 93.3 82.7 74.6 87.5 All nitrogen sources 158.1 152.7 153.2 152.3 149.0 

Nitrogen loss pathways 

 Nitrogen in crop yield removed at harvest 110.8 102.8 110.7 115.8 104.1  Nitrogen loss by volatilization 6.8 7.6 6.6 6.5 6.3 

 Nitrogen loss through denitrification processes 2.7 2.8 1.9 2.2 3.2  Nitrogen lost with windborne sediment 2.1 0.9 3.7 0.8 0.8  Nitrogen loss with surface runoff , including waterborne sediment 10.2 13.9 5.6 12.1 6.9 

 Nitrogen loss in subsurface flow pathways 20.6 22.6 18.6 14.2 27.3  Total nitrogen loss for all pathways except harvest 42.4 47.8 36.4 35.8 44.5  Change in soil nitrogen 3.8 0.8 5.1 0.0 -0.6 

Phosphorus (average annual pounds/acre) 

Phosphorus applied as commercial fertilizer and manure 21.8 22.4 21.4 20.7 20.5 Phosphorus loss pathways 

Phosphorus in crop yield removed at harvest 18.0 16.3 17.8 17.7 17.0 Phosphorus lost with windborne sediment 0.4 0.2 0.7 0.2 0.2 Phosphorus lost with surface runoff, including waterborne sediment and soluble phosphorus in surface water runoff and lateral flow into 

drainage ditches 2.7 4.1 1.6 3.2 2.1 Soluble phosphorus loss to groundwater 0.0 0.0 0.0 0.0 0.0 Total phosphorus loss for all pathways except harvest 3.1 4.3 2.3 3.4 2.3 Change in soil phosphorus 0.5 1.6 1.2 -0.5 1.2 

Pesticides 

Average annual amount of pesticides applied (grams of active ingredient/hectare) 1,748 1,743 1,570 1,690 2,014 Pesticide loss 

Average annual mass loss of pesticides for all pathways (grams of active ingredient/hectare) 10.9 9.2 5.9 13.7 8.8 Edge-of-field pesticide risk indicator 

Average annual surface water pesticide risk indicator for aquatic ecosystem 2.1 2.0 2.7 2.6 2.7 Average annual surface water pesticide risk indicator for humans 0.5 0.3 0.3 0.7 0.4 

Average annual groundwater pesticide risk indicator for humans 0.2 0.1 0.1 0.1 0.4