Weixia Zhao, Jiusheng Li, Xiumei Li, Yanfeng Li

　　State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin, China Institute of Water Resources and Hydropower Research, Beijing, Chia

　　Efficient management of variable-rate irrigation (VRI) is a critical factor for maximizing the benefit of a VRI system. A center-pivot VRI system was employed to deliver variable rates of irrigation across the field and the response of winter wheat to different irrigation trigger points was studied. The 1.64-ha experimental field with relatively large variability in available water holding capacity (AWC) was delineated into three management zones with AWC varying from 152 mm to 161 mm for zone 1, from 161 mm to 171 mm for zone 2, and from 171 mm to 185 mm for zone 3. Each zone was divided into several sub-zones to test whether different irrigation trigger points should be used for the zones with different AWC ranges. In the experiments, four irrigation trigger points of 0.55, 0.65, and 0.75 of field capacity as well as rainfed treatments were employed. For a given management zone, a higher trigger point did not necessarily result in a greater seasonal water application, especially in zone 3 where an approximately similar irrigation amount of 360-376 mm was observed for all sub-zones irrigated at different trigger points. For all management zones, the minimum plant height, yield and water productivity were always obtained in the rainfed treatments. Significant difference in plant height, SPAD and canopy temperature was detected among irrigated sub-zones, while significant difference in yield and water productivity was only obtained in zones 2 and 3. Our results suggested that managing the zones with high AWC values at high irrigation trigger points is benefit to maximizing water productivity of winter wheat across the field.