DEVELOPMENT AND EVALUATION OF DRAINAGE-N MODEL FOR PREDICTING NO NO3-N CONCENTRATIONS AND LOSSES IN SUBSURFACE DRAINAGE WATER

The DRAINAGE model was used to develop the DRAINAGE-N model with capab ility to simulate NO3-N concentrations in subsurface drain flows by in corporating the nitrogen component from the GLEAMS model. Field data o n NO3-N concentrations in subsurface drain water were used to calibrat e and validate the DRAINAGE-N model for the growing seasons of 1984, 1 986, 1987, 1990, and 1991. Simulated NO3-N concentrations and losses w ith subsurface drain flows were compared with the measured values. Pre dicted daily NO3-N concentrations in the subsurface drain water by the DRAINAGE-N model were close to the observed NO3-N concentrations valu es (difference over all years -5.7%). Predicted seasonal NO3-N losses with subsurface drain flows were also in close agreement with the obse rved data (difference over all years -1.1%). Statistical measures RMSE , EE 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 wer e within one standard deviation of the means of observed concentration s, 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.