FIELD TESTING OF DRAINMOD-N

This study was conducted to evaluate the performance of DRAINMOD-N, a nitrogen fate and transport model for artificially drained soils, base d on a comparison between predicted and observed hydrologic and nitrog en variables for an experimental site in eastern North Carolina. The s ite consisted of six plots drained by subsurface drain tubes 1.25 m de ep and 23 m apart. Each plot was instrumented to measure water table d epth, subsurface drainage, surface runoff and subirrigation rates. The re were two replications of three water management treatments: convent ional drainage, controlled drainage and subirrigation. Crops were wint er wheat followed by soybean. Results showed the model did a good job in describing the hydrology of the site. On average the predicted dail y water table depths were within 0.13 m of observed during the 14-mont h study period. Differences between predicted and observed cumulative subsurface drainage and surface runoff volumes were less than 0.10 and 0.09 m, respectively, for all treatments. Predictions for the movemen t and fate of nitrogen were also in good agreement with measured resul ts. Simulated nitrate-nitrogen (NO3-N) losses in subsurface drainage w ater were within 1.5 kg/ha of the observed values for the 14-month per iod. Differences between simulated and observed total NO3-N losses (su bsurface drainage plus surface runoff) were within 3.0 kg/ha. Results of this study indicated DRAINMOD-N could be used to simulate nitrogen losses in poorly drained soils with artificial drainage. The model, ho wever needs to be tested for longer periods of time and under differen t climatic conditions and soil types, before it can be recommended for general use.