EVALUATION OF THE EPIC MODEL FOR SIMULATING CROP YIELD AND IRRIGATION DEMAND

Abstract

An understanding of water needs in agriculture is a critical input in resolving the water resource issues that confrontmany southeastern states. Unfortunately, how much water is required and how much water is actually being used forirrigation in Georgia is primarily estimated and largely unknown. The objective of this study was to evaluate the performanceof the Environmental Policy Integrated Climate (EPIC) model in simulating crop yield and irrigation demand for three majorcrops 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 experimentstations were used to evaluate simulation of yield and irrigation amount. The root mean squared deviation (RMSD) foryield 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 themodel tended to underestimate high yields and was not as sensitive to the factors responsible for the year-to-year variabilityof 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 meansquared 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 afield level. Future efforts will focus on using the model for regional estimation of water use for irrigation in Georgia and othersoutheastern states.