DEVELOPMENT AND EVALUATION OF ENVIRO-GRO, AN INTEGRATED WATER, SALINITY, AND NITROGEN MODEL

Development of a multicomponent model for crop yield and potential gro undwater degradation applicable for irrigated agriculture is important . The ENVIRO-GRO model was developed to simulate (i) water, salt, and N movement through soil with a growing plant; (ii) plant response to m atric potential, salinity, and N stresses; (iii) drainage and salt and N leaching; and (iv) cumulatively relative transpiration and relative N uptake, and consequent crop relative yield. This model does not acc ount for denitrification. The utility of the model was illustrated by simulating the effects of irrigation amount, irrigation salinity, and N application on yield and N leaching. The results demonstrated the ef fects of complex interactions and feedback mechanisms in the plant-soi l-water-salinity-N system. Factors leading to reduced plant grow-th ca used lower transpiration, which created more leaching of salts and N. The simulated interactions are consistent with observed behaviors. Eva luation was done by comparing simulated results with published results of an experiment that had N application rates of 0, 90, 180, and 360 kg N ha(-1) and water application rates of 21, 63, and 105 cm. Agreeme nt between simulated and observed corn (Zea mays L.) relative yield an d total N uptake was generally good. The difference between mean obser ved and predicted values was <0.06 for corn relative yield and 1.34 kg N ha(-1) for total N uptake. Linear regression analyses revealed exce llent agreement results for the 63-cm irrigation and a tendency for th e model to overpredict results for the 21-cm irrigation and underpredi ct results for the 105-cm treatment.