FIELD TESTING OF DRAINMOD-N

Abstract

This study was conducted to evaluate the performance of DRAINMOD-N, a nitrogen fate and transport modelfor artificially drained soils, based on a comparison between predicted and observed hydrologic and nitrogen variablesfor an experimental site in eastern North Carolina. The site consisted of six plots drained by subsurface drain tubes1.25 m deep and 23 m apart. Each plot was instrumented to measure water table depth, subsurface drainage, surfacerunoff and subirrigation rates. There were two replications of three water management treatments: conventionaldrainage, controlled drainage and subirrigation. Crops were winter wheat followed by soybean. Results showed themodel did a good job in describing the hydrology of the site. On average the predicted daily water table depths werewithin 0.13 m of observed during the 14-month study period. Differences between predicted and observed cumulativesubsurface drainage and surface runoff volumes were less than 0.10 and 0.09 m, respectively, for all treatments.Predictions for the movement and fate of nitrogen were also in good agreement with measured results. Simulated nitratenitrogen(NO3-N) losses in subsurface drainage water were within 1.5 kg/ha of the observed values for the 14-monthperiod. Differences between simulated and observed total NO3-N losses (subsurface drainage plus surface runoff) werewithin 3.0 kg/ha.<br><br>Results of this study indicated DRAINMOD-N could be used to simulate nitrogen losses in poorly drained soils withartificial drainage. The model, however, needs to be tested for longer periods of time and under different climaticconditions and soil types, before it can be recommended for general use.