Nutrient losses from row crop agriculture in Indiana

Agricultural nutrient losses contribute to hypoxia in the Gulf of Mexico and eutrophication in the Great Lakes. Our objective was to assess effects of topography, geomorphology, climate, cropping systems and land use and conservation practices on hydrology and nutrient fate and transport in the St. Joseph River watershed. We monitored five sites (298 to 4,300 ha [736 to 10,600 ac]) on two drainage ditches within the St. Joseph River watershed in northeastern Indiana. Row crop agriculture, primarily corn (Zea Mays L.) and soybean (Glycine max [L.] Merr.), is the dominant land use (similar to 60%) in this pothole or closed depression landscape. The hydrology is dominated by subsurface tile drainage supplemented with surface drainage of remote potholes. Vegetative buffer strips have been implemented along >60% of the agricultural drainage ditches. The vegetative buffer strips play an invaluable role protecting water quality though by acting as natural setbacks during fertilizer and pesticide applications. Multiple regressions indicated land cropped to corn and areas with direct drainage or potholes are highly sensitive to nutrient losses. Future conservation assessment efforts in this and similar watersheds should focus on management of potholes in cropped fields and the subsequent effect of those practices on tile drainage water.