Subsurface Drain Flow and Nitrogen Losses Simulation Using DRAINMOD/DRAINMOD-N

This study was conducted to evaluate the performance of DRAINMOD /DRAINMOD-N on an experimental drainage field at Southeast Purdue Agricultural Center (SEPAC), based on the comparison between observed and predicted subsurface drain flows and nitrate-nitrogen losses via drainage. The site was under conventional drainage management, consisting of two replications of three tile drain spacings—5m, 10m and 20m at 75cm depth. Six observation wells were installed to measure subsurface drain flow and to obtain flow-proportional drainage water quality samples. The model simulations conducted for the Clermont silt loam soil of Indiana predicted daily subsurface drain flows within standard errors of 0.02 to 0.06cm/day during four years study period for the tile spacing of 20m. The average absolute deviations between predicted and observed drain flows were within 0.01 to 0.04cm/day. The simulated cumulative nitrogen losses in drainage were within 14% of the observed values.