Nitrogen Use Efficiency, Yield, and Water Quality in Midwest Tile-Drained Landscapes.

Much of the nitrate found in streams and rivers of the US Midwest comes from leaching of N fertilizers applied to corn (Zea Mays L.).  To reduce this leaching, N-fertilizer must be used more effectively.  Two approaches have been suggested for improving N use efficiency in corn.  The first approach divides the field into smaller areas that respond to N management more uniformly via precision agriculture.  This is based on the observation that corn yields are temporally and spatially stable and the assumption that these yield patterns are indicative of N fertilizer responsiveness.  The second approach applies N fertilizer closer to the time when the crop N need is greatest.  When combined with a method for determining the appropriate N rate, such as soil testing or crop sensing, this approach should result in optimal N use efficiency.  This presentation evaluates both approaches for optimizing crop yield while reducing N losses to surface waters within the highly productive, rain-fed, tile-drained soils of the US Midwest.