Using Winter Cover Crops for Improving Soil and Water Quality at Different Topographic Positions on the Watershed Scale.

Corn (Zea mays L.) and soybean (Glycine max L.) production in the Upper Midwest is a major contributor of nutrient leaching to groundwater and poses an environmental threat such as eutrophication and hypoxia in Gulf of Mexico. Seasonal change and topography play important role in regulating nutrient leaching. The interval between crop harvest in fall and planting in spring is a critical time for leaching of nutrients, especially in areas with high precipitation. A promising strategy to control nitrate leaching and sediment runoff loss during winter fallow periods is use of cover crops. The overall objective of this study was to evaluate nutrient leaching with and without cover crop (cereal rye) on various slope positions (shoulder, back, and deposition) delineated using topographical position index in ArcGIS on watershed scale. A field experiment was conducted in 2015 at agricultural research site adjacent to Southern Illinois University’s tree improvement center located on west side of the City of Carbondale, IL. Soil samples collected after corn/soybean harvest and after cover crop burning were used for analysis of standard soil fertility parameters. Nutrient concentration in soil solution were measured from eighteen suction lysimeters installed at 30 cm depth at three topographic positions. Soil solution samples were collected weekly or biweekly depending on the amount of precipitation and were analyzed for pH, EC, anions (Br^-, Cl^-, F^-, NO₂^- , NO₃^-, SO₄^2-, and PO₄^3-), dissolved reactive phosphorus, total nitrogen and dissolved organic carbon. Volumetric water content and electrical conductivity were also measured. Preliminary results from this study showed that cereal rye planted in fall 2015 reduce NO₃-N leaching at all the topographic positions at varying degrees when compared to no cover-crop treatment. Nitrate-N leaching was highest at the shoulder position followed by deposition slope position and was lowest at the backslope position. This study will help in understanding the contribution of cover crops on watershed scale in reducing nutrient leaching and improving surface water quality by scavenging nutrients from soil profile.