Modeling nitrate nitrogen leaching in response to nitrogen fertilizer rateand tile drain depth or spacing for southern Minnesota, USA

The Agricultural Drainage and Pesticide Transport (ADAPT) simulation model was used to evaluate the relative efforts of nitrogen application rate, til e-drain sparing, and tile-drain depth on NO3-N losses through tile drains f or conditions that are typical of the Upper Midwestern USA. The ADAPT model , a daily time-step continuous water table management model, was calibrated and validated for tile drainage and associated NO3-N losses using long-ter m monitoring data measured on three experimental plots of a Webster clay lo am (fine-loamy, mixed, superactive, mesic Typic Endoaquoll) under continuou s corn (Zea mays L.) with conventional tillage treatment. For the calibrati on period, the model predicted mean monthly tile drainage and NO3-N losses of 4.6 cm and 6.7 kg ha(-1), respectively, against measured tile drainage a nd NO3-N losses of 4.6 rm and 6.9 kg ha(-1), respectively. For the validati on period, the predicted mean monthly tile drainage and NO3-N losses were 4 .0 cm and 6.1 kg ha(-1), respectively, against measured tile drainage and N O3-N losses of 3.7 cm and 6.5 kg ha(-1), respectively. Long-term simulation s were made for a wide range of climatic conditions between 1915 and 1996 t o evaluate the effect of drain sparing, drain depth, and N application rate s on tile drainage and NO3-N losses. Simulation results indicate that much greater reductions in NO3-N losses occur with reduced N application rates t han with increases in drain spacing or decreases in drain depth.