Deficit Irrigation and Supplemental Irrigation Management for Rainfed and Irrigated Wheat in Selseleh Region

In order to improve irrigation water productivity and to allocate the saved water to limited irrigation of the adjacent areas, different deficit irrigation methods were studied under surface and sprinkler irrigation systems for two wheat cultivars (Pishtaz and Shiraz), during 2006-07, in Selseleh region located in Lorestan province, Iran. The objectives of this study were to find the optimum water depth in sprinkler irrigation and non-effective irrigation in surface irrigation. Different levels of irrigation water were studied under sprinkler irrigation by using a single source. The treatments of surface irrigation included full irrigation, withholding the first irrigation in spring, withholding the first and third irrigation in spring time. The grain yield, irrigation water use, and water productivity were measured in different treatments. Under sprinkler irrigation, optimum level of deficit irrigation was realized with 29.4% of full irrigation treatment (220.5 mm). Under surface irrigation, withholding of the first spring irrigation (78 percent of full irrigation) was the optimum treatment. Under surface irrigation, deficit irrigation led to 22% irrigation water saving and 3.3% increase in grain yield. Root expansion in the deficit irrigation treatments and, consequently, increase in effective soil moisture availability limited grain yield reduction. Under deficit irrigation, deep root expansion was 10.5 percent more than full irrigation condition. Increasing the effective soil depth prevented yield decline. Water saving by deficit irrigation can be used for single irrigation of adjacent rainfed areas (at planting time or critical stages of spring time), which increases total water productivity by 9.3%.