An Evaluation of the EPIC Model for Soybeans Grown in Southern Piedmont Soils

Abstract

The Erosion Productivity Impact Calculator (EPIC) model was designed to evaluate the loss of crop productivity due to soil erosion. EPIC uses information on weather, soils, nutrients, topography, and other site characteristics to estimate crop growth and yields. In this study, the EPIC model was applied to the problem of estimating soybean yields from the Southern Piedmont of Georgia. Measured yields from a two-year period with 24 farm fields per year were compared to predicted yields. The measured data included triplicated results from slight, moderate, and severe erosion class soils on each field. The model predicted correctly relative differences in crop yields between erosion classes and between years. However, the model tended to under predict for high yields and over predict for low yields. Within treatment variances were higher for the measured data than for the predicted data, indicating that the model did not represent the natural variability present in the data. The model was shown to be insensitive to certain soil variables which had been previously shown to be correlated to yields using the same data set as in this study, suggesting a possible avenue for improving soybean yield predictions for conditions in the Southern Piedmont.