Crop conversion impacts on runoff and sediment loads in the Upper Sunflower River watershed

Abstract

The Mississippi River alluvial floodplain is one of the most productive agricultural regions in the United States. In recent decades, factors of economic forces and government policies have driven crop selection and respective farming management changes in this region. This study quantified the effects of changes in crop conversion and farming management practices to discharge and sediment loads in the Upper Sunflower River watershed. Farming and climate conditions were dynamically characterized in space and time by integrating annual crop yield at the county scale, annual crop irrigation in the field scale, and an enhanced description of precipitation. This information was used as input into the Annualized Agricultural Non-Point Source (AnnAGNPS) watershed pollution model to describe existing conditions and simulate alternative scenarios. Simulations considering high irrigation adoption indicated 15% average annual percent change increase in short-term flow during the months of June, July, and August at the outlet. Conversely, simulations considering future trends in crop conversion to corn/soybean production indicates a potential reduction in average annual sediment loads for clay and silt, respectively, to 4.6 Mg/ha and 0.41 Mg/ha from 5.5 Mg/ha and 0.44 Mg/ha for existing conditions. As irrigation increases and crop production continues to shift towards corn/soybeans, these findings support the development of responsible irrigation management strategies designed for efficient water usage coupled with implementation of in field conservation practices for reduced sediment loads.