MODIFICATION OF DRAINAGE MODEL BY USING THE NITROGEN COMPONENT FROM THE GLEAMS MODEL

The NITRO subroutine of the DRAINAGE model (Kanwar et al., 1983) was m odified using the nitrogen transformation components of the GLEAMS (Le onard et al., 1987) model to predict more accurately the leaching of N O3-N to subsurface drainage water. predicted values of tile flows and nitrate concentrations in tile effluent have shown a good agreement wi th observed data for the period from 1984 to 1992. There were some dis crepancies between the predicted and observed values in the beginning of the simulation period resulting from lack of field data for soil-pr ofile initialization. Despite the assumed steady-state condition withi n each time increment (one day) and the complexity of the drainage sys tem, the modified DRAINAGE model has shown the capability to reasonabl y estimate long-term N loss with tile effluent. Average deviation and standard error between the predicted and observed NO3-N concentrations in the tile water indicated that the modified DRAINAGE model develope d in this study resulted in better predictions of NO3-N concentrations in the drainage water than the original DRAINAGE model.