In the United States,nutrient loss from agricultural fields contributes to a “dead zone” of low dissolved oxygen concentrations near the mouth of the Mississippi River in the Gulf of Mexico.In August 2015,this area reached 16,760 km2,the largest area recorded since 2002.Efforts are underway in many states within the Mississippi River basin to reduce crop nutrient loss.In Tennessee,Soil and Water Assessment Tool(SWAT)water quality models have been developed to evaluate the nutrient load reduction for winter wheat cover crops on corn and soybean fields in the Red River and South Fork of the Obion River watersheds,which are dominated by agricultural landuse.SWAT is a physically based,watershed-scale,continuous time simulation model that links hydrology and nutrient cycling with crop growth.Model inputs included digital elevation data and United States Department of Agriculture crop satellite imagery(Croplands Data Layer)as well as a soils database.