Developing Nitrogen BMPs from Field Research Gyles W. Randall* and Jeffrey A. Vetsch, Univ. of Minnesota, Waseca, MN Abstract Best management practices (BMPs) for nitrogen (N) and their implementation are critical to achieving profitable crop production while minimizing nitrate losses to ground and surface waters. Nitrogen BMPs for corn (Zea mays) grown after soybean (Glycine max) in south-central Minnesota were developed from long-term, subsurface tile drainage research conducted at the University of Minnesota’s Southern Research and Outreach Center at Waseca. A four-year study showed significantly greater nitrate losses in tile drainage accompanied by no increase in corn yield or profitability when applied N rates exceed the University’s recommended rate. A 15-year study indicated that spring application of ammonia produced greatest yield and profit while minimizing nitrate loss to drainage compared with fall-applied ammonia without N- Serve, and thus is a preferred BMP. Fall application of ammonia with N-Serve also significantly reduced nitrate losses but is considered a BMP with RISK because yields and economic return were lower in years when May and/or June were very wet. Results from these studies clearly show application rates in excess of University recommendations and fall application of ammonia without N-Serve are not BMPs for south-central Minnesota. Experimental Procedures Soil: Canisteo clay loam, Typic Endoaquoll Years: 1987 – 2003 Tile plots: 36; 16 corn, 16 soybean and 4 grass Plot size: 30 ft. by 20 ft. simulating 50 ft. tile spacing. Isolated to a depth of 6 ft. by 12 mil plastic sheeting. Tile depth: 3.5 ft. Slope: 0 – 1 % Tile drainage research facility at Waseca. Schematic diagram of drainage plot details. 20’ 30’ 5’ Collection sump Rate and Time of Application Nitrogen Source and Time of Application Time of N Application and Nitrification Inhibitors Effect of N rate for corn after soybean on NO 3 -N concentration in tile drainage water in Purpose To determine the effect of N rate, time of application, and nitrapyrin (N-Serve) on nitrate losses to subsurface, tile drainage and on corn production. To develop best management practices (BMPs) for N for south-central Minnesota based on long-term field research. References Randall, G.W., and D.J. Mulla Nitrate-N in surface waters as influenced by climatic conditions and agricultural practices. J. Environ. Qual. 30: Randall, G.W., and J.A. Vetsch, and J.R. Huffman Nitrate losses in subsurface drainage from a corn-soybean rotation as affected by time of nitrogen application and use of nitrapyrin. J. Environ. Qual. 32: Randall, G.W., J.A. Vetsch, and J.R. Huffman Corn production on a subsurface-drained Mollisol as affected by time of nitrogen application and nitrapyrin. Agron. J. 95: Randall, G.W., and J.A. Vetsch Nitrate losses in subsurface drainage from a corn-soybean rotation as affected by fall vs. spring application of nitrogen and nitrapyrin. J. Environ. Qual. 34(2): Randall, G.W., and J.A. Vetsch Corn production on a subsurface-drained Mollisol as affected by fall versus spring application of nitrogen and nitrapyrin. Agron. J. 97: Acknowledgement Sincere appreciation is extended to Dow AgroSciences for their financial contribution to this research.