USING YIELD-STRESS MODEL TO PREDICT THE IMPACT OF DEFICIT IRRIGATION ON ONION YIELD

The impact of deficit irrigation on onion yield and consumptive use was predicted after calibration and validation of Yield-Stress model for onion data obtained from three-year field trial (1998/99, 1999/00 and 2000/01) conducted in Beni Swief governorate, Egypt. Two irrigation treatments were used in these trials (fresh and drainage water irrigation). The goodness of fit between measured and predicted onion yield and consumptive use was done by calculating percent difference between measured and predicted values, root mean square error and Willmott index of agreement. Four deficit irrigation treatments were tested (95, 90, 85 and 80 % of full irrigation). The results showed that three was a good agreement between measured and predicted values by Yield-Stress. The results also indicated that applying 80 % of full irrigation of either fresh or drainage irrigation resulted in low yield losses. Furthermore, water use efficiency was the highest under irrigation with 80 % of full irrigation. Therefore, 20 % of the applied fresh or drainage irrigation water could be saved and used in irrigating new reclaimed areas.