DRAINMOD-N II: Evaluated for an Agricultural System in Iowa and Compared to RZWQM-DSSAT
2009
A new simulation model for N dynamics, DRAINMOD-N II, has been previously evaluated for only a few sites. We evaluated the model using ten years (1996-2005) of measured data from a subsurface-drained, corn-soybean agricultural system near Story City, Iowa. Nitrogen fertilizer was applied to plots at low, medium, and high rates (57 to 67 kg N ha -1 , 114 to 135 kg N ha -1 , and 172 to 202 kg N ha -1 , respectively) during corn years, and nitrate (NO 3 ) losses from subsurface drains under each plot were monitored biweekly for ten years. Average annual simulated and measured NO 3 losses in drainage water were 21.9 and 20.1 kg N ha -1 for the low N rate, 26.6 and 26.5 kg N ha -1 for the medium N rate, and 36.6 and 37.0 kg N ha -1 for the high N rate, respectively. The model efficiency statistics for DRAINMOD-N II simulations of annual subsurface drain NO 3 losses were 0.89, 0.95, and 0.94 for the low, medium, and high N rates, respectively. For the same experimental dataset, a comparison of DRAINMOD-N II simulations to that of another model that simulates hydrologic and N dynamics of agricultural systems, the RZWQM-DSSAT hybrid model, demonstrated that the two models were most different in their simulations of soybean N fixation, plant N uptake, and net N mineralization. Future field investigations should focus on generating better understandings of these processes. The results suggest that DRAINMOD-N II can reasonably simulate the effects of different corn-year N rates on losses of NO 3 through subsurface drainage lines and that simulations of subsurface drainage NO 3 losses by DRAINMOD-N II are comparable to that of RZWQM-DSSAT.
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