EVALUATION OF GLEAMS AND PRZM FOR PREDICTING PESTICIDE LEACHING UNDERFIELD CONDITIONS

Pesticide simulation models, GLEAMS and PRZM, were evaluated for their ability to predict pesticide behavior using field data from a plot un der no-till corn in the Coastal Plain region of Virginia. The models w ere evaluated in an uncalibrated mode as well as with adjustment of im portant hydrology parameters. The evaluation of model performance was based on graphical displays and statistical measures. Difference in ev apotranspiration (ET) predictions by the two models caused the simulat ed results from their hydrology components to vary. Runoff and soil mo isture measured in the field were predicted reasonably well after adju sting important hydrology parameters. Except for differences in magnit ude, both models predicted the chemical concentration profiles similar ly. Overall, GLEAMS represented pesticide behavior in soil better than PRZM. The models, GLEAMS and PRZM, performed well in predicting pesti cide mass in the root zone, but were less reliable in predicting pesti cide concentration distributions in soil. Model predictions of pestici de fate and transport were not greatly affected by changes in curve nu mber and the water holding capacity of the soil.