DEVELOPMENT AND EVALUATION OF DRAINAGE-N MODEL FOR PREDICTING NO3-N CONCENTRATIONS AND LOSSES IN SUBSURFACE DRAINAGE WATER

Abstract

The DRAINAGE model was used to develop the DRAINAGE-N model with capability to simulate NO3-N concentrations in subsurface drain flows by incorporating the nitrogen component from the GLEAMS model. Field data on NO3-N concentrations in subsurface drain water were used to calibrate and validate the DRAINAGE-N model for the growing seasons of 1984, 1986, 1987, 1990, and 1991. Simulated NO3-N concentrations and losses with subsurface drain flows were compared with the measured values. Predicted daily NO3-N concentrations in the subsurface drain water by the DRAINAGE-N model were close to the observed NO3-N concentrations values (difference over all years –5.7%). Predicted seasonal NO3-N losses with subsurface drain flows were also in close agreement with the observed data (difference over all years –1.1%). Statistical measures RMSE, EF, and CD were calculated for 5 years of combined seasonal values of NO3-N concentrations and values for these parameters were 0.12, 0.34, and 1.5, respectively. Predicted soil profile NO3-N concentrations were within one standard deviation of the means of observed concentrations, with a few exceptions. Overall results of this study indicate that the DRAINAGE-N model has good potential for simulating long-term NO3-N concentrations and losses with the subsurface drain flows.