Maximizing water productivity of winter wheat by managing zones of variable rate irrigation at different deficit levels

To determine the specific application rate for each management zone of a variable rate irrigation system, the yield and water use efficiency (WUE) of winter wheat were evaluated during two growing seasons at different deficit levels in the alluvial flood plain of the North China Plain. One 1.64-ha quadrant irrigated by a variable rate center pivot system was delineated into four management zones with available soil water holding capacity, and varied soil profiles were detected in these zones. Each zone was divided into several subzones to be irrigated at different deficit levels. In the 2016 season, each subzone was managed individually with irrigation trigger points of 55%, 65%, 75%, and 80% of field capacity along with a rain-fed treatment. In the 2017 season, all subzones were irrigated simultaneously with 0%, 33%, 67%, 100%, and 120% of the base application depth. For the two-season study, the rain-fed treatment produced significantly lower yield and WUE than the irrigated treatments, and both the maximum yield and the maximum WUE were obtained in zone 2, where a more uniform soil profile was detected. A linear crop water production function was determined for zones 1 and 3 in the 2017 season, while a quadratic equation fit the crop water production function well for other zones in the two seasons. The relationship between WUE and crop water use in the three zones can be represented by a curvilinear equation for both seasons. Taking the optimal application rate of maximizing WUE in zone 1 as a basis, 89% and 94% of the rate in zone 1 was recommended for zones 2 and 3, respectively, to achieve the maximum WUE in the entire field. Our results also suggested that the existing layered-textural soil profile can greatly influence crop productivity and should therefore be considered in mapping irrigation prescriptions.