USING CROP MODELS TO PLAN WATER WITHDRAWALS FOR IRRIGATION IN DROUGHTYEARS

Knowledge of water demands during periods of severe drought is needed to develop strategies for water management. The potential (no-water st ress) and the lowest (no irrigation) yields for corn, soybean and pean ut were calculated using three crop growth and water use models-CERES- Maize, SOYGRO, and PNUTGRO. Rainfall, temperature, and solar radiation records were used with these models to identify the 15 most severe dr ought years in the 53 year record in a 36-county region of Georgia tha t contains almost 75% of Georgia's irrigated land. In the 15 driest ye ars, simulated yield losses averaged 75%for corn, 73%for soybean, and 64% for peanut. Irrigation amount and timing needed to provide 90% of the no-stress yields were calculated. Most of the irrigation needs of corn in these drought years occurred before that of peanut or soybean. For the reported irrigated crop acreage of the study area, simulated water withdrawals exceeded 3 million m3 per day, on the average, for m ost of the 130 days between late May and late September. Further appli cation of the techniques used here could lead to regional or watershed specific estimates of maximum water needs.