Pre-sowing soil water conditions and water conservation measures affecting the yield and water productivity of summer maize

The annual double cropping of winter wheat and summer maize plays an important role in ensuring the food supply in the North China Plain (NCP). With the intensifying water shortage, a deficit irrigation strategy has been gradually applied to this cropping system. The limited irrigation water supply generally results in a dry root zone soil profile at winter wheat harvesting which further negatively affects the grain production of its following crop, summer maize. Field studies from 2016 to 2019 at a typical site in the NCP (Luancheng Agro-experimental station) were undertaken to examine the effects of different irrigation schedules during the winter wheat season on summer maize production, and water conservation techniques that might benefit maize production under a limited water supply. The results indicated that soil water contents at maize sowing played an important role in deciding the final maize yield. Under the recommended winter wheat deficit irrigation schedule for this region, the yield of maize would be reduced by 22-32% compared to the maize following the full irrigation schedule. Water deficits mainly occurred during the earlier growth stage of maize, before the rainfall season. Reducing water consumption during the earlier growth stages of maize was important for prolonging the soil water availability for crop growth from the irrigation at maize sowing. Due to the smaller canopy cover at the earlier maize growth stages, using straw from the winter wheat to fully cover the soil surface was an active measure to preserve soil moisture, and the maize yield under mulch was increased by 10-25%, while the water use efficiency (WUE) was increased by 5-25%. Under a limited water supply, reducing planting density by 11% over the normal density could reduce crop water use during the vegetative stage and increase crop water use during the reproductive stage, which increased grain production and water productivity. The reduced density also decreased the production cost. These results indicate that measures to preserve soil water during the vegetative growth stages of maize would benefit grain production under limited water supply conditions in the NCP.