Modeling nitrate-nitrogen losses in response to tile drain depth and spacing in a cold climate

The Agricultural Drainage and Pesticide Transport (ADAPT) model was used to evaluate the effects of tile drain spacing and depth on NO₃-N losses in southeastern Minnesota. The model was calibrated and validated using 4 years of monthly flow and nitrate loss data from two tile drained fields (11 and 9.3 ha) in Nicollet County. Half the monitoring data from the 11 ha field were used for calibration and half for validation of the model. The model was also validated using independent monitoring data from the 9.3 ha field. For the calibration period on the 11 ha field, the model predicted mean monthly tile drainage and NO₃-N losses of 141.5 m³/day and 5.2 kg/ha, respectively, against measured tile drainage (126.2 m³/day) and NO₃-N losses (4.5 kg/ha). For validation, the predicted mean monthly tile drainage and NO₃-N losses were 131.7 m³/day and 4.4 kg/ha, respectively, against measured tile drainage and NO₃-N losses of 80.4 m³/day and 3.0 kg/ha, respectively. Similar validation results were found with 9.3 ha field. Long-term simulations were made for a wide range of climatic conditions (1954-2003) to evaluate the effects of drain spacing and drain depth on tile drainage and NO₃-N losses. Simulations results indicate that increasing spacing and decreasing depth of tile drains reduces the tile drainage and NO₃-N losses, and can serve as a remedy to the excess NO₃-N losses.