Evaluation of the epic model for simulating crop yield and irrigation demand

An understanding of water needs in agriculture is a critical input in resolving the water resource issues that confront many southeastern states. Unfortunately, how much water is required and how much water is actually being used for irrigation in Georgia is primarily estimated and largely unknown. The objective of this study was to evaluate the performance of the Environmental Policy Integrated Climate (EPIC) model in simulating crop yield and irrigation demand for three major crops in Georgia. Model evaluation is necessary to provide credibility in applying the model for simulating water use by agriculture. Seasonal yield and irrigation data for the 1990 through 2001 crop variety trials conducted at five agricultural experiment stations were used to evaluate simulation of yield and irrigation amount. The root mean squared deviation (RMSD) for yield was 0.29 t/ha for cotton, 0.39 t/ha for soybean, and 1.02 t/ha for peanut. The RMSD for peanut was large because the model tended to underestimate high yields and was not as sensitive to the factors responsible for the year-to-year variability of peanut yield. The RMSD for total amount of irrigation was 75 mm for cotton, 83 mm for soybean, and 87 mm for peanut. The model simulated the mean irrigation amount and the magnitude of annual variability very well. The component of mean squared deviation (MSD = RMSD2) related to the pattern of annual variability in irrigation amount contributed most to MSD. Overall, the results showed that the EPIC model can be a useful tool for simulating crop yield and irrigation demand at a field level. Future efforts will focus on using the model for regional estimation of water use for irrigation in Georgia and other southeastern states.