Modification OF Epic TO SIMULATE PESTICIDE ACTIVITIES: EPIC-PST

The need for a mathematical model capable of simulating simultaneously the effects of different agricultural management practices on crop yield, and chemical (nutrients and pesticides) losses by surface runoff, sediment movement and leaching below the rootzone has prompted the development of EPIC-PST. This model was developed by using EPIC as a building block and adopting from the GLEAMS model the pesticide related subroutines. EPIC-PST was evaluated by a) validating the incorporation of GLEAMS pesticide subroutines into EPIC; b) comparing chemical losses by runoff and chemical concentration in the soil profile widi observed data from Ben Hur Research Farm, near Baton Rouge, Louisiana; and c) comparing chemical concentration in the soil profile with observed data from Dorminey farm near Tifton, Georgia. It was concluded from the evaluation that the incorporation of GLEAMS pesticide-related subroutines was successfully accomplished. EPIC-PST overestimated total Atrazine loss in runoff by 7% and underestimated total Metolachlor loss in runoff by 8% when compared to the values observed at Ben Hur Research Farm. For both sites, comparison of observed and predicted pesticide concentrations in the soil profile has shown that the model is apparently simulating faster movement of chemical through the rootzone than that observed in the field. However, the patterns in the changes of chemical concentration with time were similar to the observed.