Estimating Agricultural Water Use for Major Crops in the Southeastern USA: A Simulation Approach.

Agricultural water use is a critical issue in Georgia due to the continuous drought experienced during the last decade. The increasing water needs for irrigation as well as other sectors has prompted efforts to estimate the future demand for agricultural water use as a part of a comprehensive water policy plan for the state of Georgia.  The aim of this study was to estimate the water use for irrigation for the major crops grown in Georgia. The crop simulation models of the Decision Support System for Agrotechnology Transfer (DSSAT) Version 4.5 were used to simulate irrigation requirements for maize, cotton, peanut and soybean.  112 counties that represent the most important agricultural production region in Georgia were selected to run the simulations. Historical daily weather data, three representative soil profiles, and specific crop management were used as input for the simulations. The irrigation output of the model was compared with observed data from the Agricultural Water Pumping project that was conducted from 2000 to 2004. The daily outputs of the models were used to calculate the monthly and yearly irrigation requirements for each crop. The correlation coefficient for corn, for the five counties, where the model was evaluated, ranged between 0.87 and 0.93. After evaluation, the models were used to simulate crop yield and irrigation requirements for each cropping season from 1950 to 2007. The daily outputs of the models were then used to calculate the monthly and yearly irrigation requirements for each crop. For each county, monthly and yearly statistics were calculated. Although the observed data were limited to a short period of years, the simulated data were in within acceptable ranges of the observed data.  The total season amount of water indicates that corn was the crop that required most of the irrigation, followed by cotton, peanut and soybean.