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The Erosion Productivity Impact Calculator (EPIC) model has been successfully applied for agricultural policy analyses for more than a decade. EPIC has been tested and validated under a wide range of conditions; however, there is an ongoing need to further test the model to improve its prediction capabilities. In this study, EPIC was calibrated and validated using 3 years (1990–1992) of data collected from a field site near Nashua, Iowa. The model’s performance was evaluated by assessing its ability to replicate the effects of various tillage and crop rotation systems on subsurface tile flow, nitrate–nitrogen (NO3–N) loss with tile flow, and crop yield. Predicted annual average tile flows and nitrate losses in the...
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[1] Over the last century, land use and land cover (LULC) in the United States Corn Belt region shifted from mixed perennial and annual cropping systems to primarily annual crops. Historical LULC change impacted the annual water balance in many Midwestern basins by decreasing annual evapotranspiration (ET) and increasing streamflow and base flow. Recent expansion of the biofuel industry may lead to future LULC changes from increasing corn acreage and potential conversion of the industry to cellulosic bioenergy crops of warm or cool season grasses. In this paper, the Soil and Water Assessment Tool (SWAT) model was used to evaluate potential impacts from future LULC change on the annual and seasonal water balance...
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The research was conducted as part of the USDA's Conservation Effects Assessment Project. The objective of the project was to evaluate the environmental effects of land-use changes, with a focus on understanding how the spatial distribution throughout a watershed influences their effectiveness. The Soil and Water Assessment Tool (SWAT) water quality model was applied to the Squaw Creek watershed, which covers 4,730 ha (11,683 ac) of prime agriculture land in southern Iowa. The model was calibrated (2000 to 2004) and validated (1996 to 1999) for overall watershed hydrology and for streamflow and nitrate loadings at the watershed outlet on an annual and monthly basis. Four scenarios for land-use change were evaluated...
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This paper provides estimates of the cost associated with inducing substantial conversion of land from production of traditional crops to switchgrass and its potential environmental consequences. Higher traditional crop prices due to increased demand for corn from the ethanol industry has increased the relative advantage that row crops have over switchgrass. Results indicate that farmers will convert to switchgrass production only with significant conversion subsidies. Potential environmental consequences of this conversion were analyzed using three stylized landscape usage scenarios, one with an entire conversion of a watershed to switchgrass production, a second with the entire watershed planted to continuous...
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Nonpoint source pollution in intensively managed agricultural landscapes is of great concern to the general population, farmers and policymakers, as it impacts local water quality and can have large downstream effects, as in the case of hypoxia in the Gulf of Mexico. In this study, we outline a methodology to simultaneously assess economic costs and water quality benefits associated with the hypothetical placement of a broad set of conservation practices. The study, performed for the Iowa Department of Natural Resources, assesses thirteen major subbasins in Iowa by interfacing economic models with the Soil and Water Assessment Tool model. The conservation practices analyzed include land set-aside, terraces, grassed...
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