Effect of soil water deficit on evapotranspiration, crop yield, and water use efficiency in the North China Plain

In the North China Plain (NCP), excessive groundwater pumping is a serious problem. In this study, different groundwater irrigation schedules were applied. A simple soil water balance approach was introduced to evaluate crop evapotranspiration (ET) and water use efficiency (WUE). Under normal irrigation scheduling, groundwater mining occurs at a rate of over 200 mm per year from a rapidly depleting aquifer system. Severe soil water deficit (SWD) decreases grain yield (GY) of wheat (Triticum aestivum L.) and maize (Zea mays L.), while slight SWD in a growth stage from spring green up to grain-filling winter wheat did not evidently reduce GY and WUE. A severe or slight SWD significantly reduces ET, which mainly depends on irrigation amounts. Thus, it is possible to reduce ET somewhat without significantly decreasing GY. ET was correlated to GY in a parabolic function, and maximum yield for winter wheat occurred when optimal ET for winter wheat was about 447 mm. It was important for wheat and maize to be irrigated before sowing to improve soil water storage (SWS), and the effect of the irrigation apparently increased wheat GY.