AN EVALUATION OF THE EPIC MODEL FOR SOYBEANS GROWN IN SOUTHERN PIEDMONT SOILS

The Erosion Productivity Impact Calculator (EPIC) model was designed t o evaluate the loss of crop productivity due to soil erosion. EPIC use s information on weather, soils, nutrients, topography, and other site characteristics to estimate crop growth and yields. In this study, th e EPIC model was applied to the problem of estimating soybean yields f rom the Southern Piedmont of Georgia. Measured yields from a two-year period with 24 farm fields per year were compared to pre&cted yields. The measured data included triplicated results from slight, moderate, and severe erosion class soils on each field The model predicted corre ctly relative differences in crop yields between erosion classes and b etween years. However, the model tended to under predict for high yiel ds and over predict for low yields. Within treatment variances were hi gher for the measured data than for the predicted data, indicating tha t the model did not represent the natural variability present in the d ata. The model was shown to be insensitive to certain soil variables w hich had been previously shown to be correlated to yields using the sa me data set as in this study, suggesting a possible avenue for improvi ng soybean yield predictions for conditions in the Southern Piedmont.