ESTIMATING NITROGEN PERCOLATION RELATIONSHIPS - AN APPLICATION OF TOBIT ANALYSIS

Regression analysis is used to complement a simulation model by synthe sizing a large amount of ta into concise results. The crop growth/chem ical fate simulation model EPIC-PST is used to estimate annual nitroge n percolation loadings under irrigated wheat and corn production for v arious soil types, irrigation systems, and management Practices. Tobit analysis synthesized these results and provided information about the effect of selected variables (e.g. irrigation level and nitrogen appl ied) on the expected value and the probability of nitrogen percolation events. The tobit results can be used to make field recommendations a nd policy prescriptions based on EPIC-PST output.