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

The Agricultural Drainage and Pesticide Transport (ADAPT) simulation model was used to evaluate the relative effects of nitrogen application rate, tile-drain spacing, and tile-drain depth on NO₃-N losses through tile drains for 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-term monitoring data measured on three experimental plots of a Webster clay loam (fine-loamy, mixed, superactive, mesic Typic Endoaquoll) under continuous corn (Zea mays L.) with conventional tillage treatment. For the calibration period, the model predicted mean monthly the drainage and NO₃-N losses of 4.6 cm and 6.7 kg ha^-1, respectively, against measured tile drainage and NO₃-N losses of 4.6 cm and 6.9 kg ha^-1, respectively. For the validation 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 NO₃-N losses of 3.7 cm and 6.5 kg ha^-1, respectively. Long-term simulations were made for a wide range of climatic conditions between 1915 and 1996 to evaluate the effect of drain spacing, drain depth, and N application rates on the drainage and NO₃-N losses. Simulation results indicate that much greater reductions in NO₃-N losses occur with reduced N application rates than with increases in drain spacing or decreases in drain depth.