COMPARING SIMULATED NITRATE-NITROGEN CONCENTRATION IN SUBSURFACE DRAINAGE USING DRAINMOD-N II AND RZWQM2

This study used a 16-year (1989-2004) field experiment conducted in Iowa to compare the performance of DRAINMOD-N II and Root Zone Water Quality Model2 (RZWQM2) in predicting nitrate-nitrogen (NO3-N) concentration and losses in a subsurface drained field at nine nitrogen application rates (0-252 kg N ha(-1)). Results showed that the performance of both models can 'satisfactorily' predict NO3-N concentration. The Nash-Sutcliffe efficiency (NSE), ratio of the root mean squared error to the standard deviation (RSR), and percent bias (PBIAS) for DRAINMOD-N II were 0.87, 0.36, and -2%, respectively, in simulating NO3-N concentration; and 0.84, 0.39, and -9%, respectively, in simulating NO3-N loss. By contrast, NSE, RSR, and PBIAS for RZWQM2 were 0.76, 0.49, and -3%, respectively, in simulating NO3-N concentration; and 0.64, 0.6, and -16%, respectively, in simulating NO3-N loss. This study indicated that both models can be used to simulate NO3-N loss and concentration in drainage flow at different N application rates. However, DRAINMOD-N II demonstrated slightly better performance than RZWQM2. In terms of the maximum contaminant level, the threshold N rates predicted by RZWQM2 and DRAINMOD-N II did not differ significantly from those in observations and can be used for agricultural production. This study highlights the advantages of DRAINMOD-N II in assessing the effects of nitrogen management practices. Copyright (C) 2017 John Wiley & Sons, Ltd.