Regulating mechanisms for improving farmland water use efficiency

The North China Plain (NCP) is one of the most important grain production areas in China. With decreasing supply of the limited water resources, the challenge for more grain production on less water via high water use efficiency (WUE) has never been so great in the NCP. A large gap has remained between actual WUE in the NCP and that under optimized agronomic practices. This has called strategies to either maintain or increase agricultural production with less water use. This paper examined the problems that have restricted improvements in WUE in the NCP. It further reviewed three aspects to improve WUE via regulating crop water use in the plain. One aspect was using water-nitrogen interactions to regulate instantaneous and time-integrated WUE at the leaf-canopy level. This also regulated carbon assimilation and allocation in leaf-plant-canopy system and above/below-ground systems. It in turn optimized the processes of biomass accumulation and allocation in grain production and led to the development of field management strategies for optimizing WUE. The second aspect was the management of root system for efficient utilization of soil water. Long-term mechanical tillage practices in the NCP had altered soil physical properties in the top soil layer, which had restricted deep root growth. It was necessary to adopt changes in tillage practices suitable for more efficient utilization of soil moisture by crops. The third aspect was using cultivars with traits for more efficient water use. WUE increased substantially with recent use of early-release cultivars in the NCP. There had also been larger variations in yield and WUE among modern cultivars. Positive correlations between grain yield and WUE indicated that high-yield cultivar had the potential to improve WUE, thereby saving more of the limited water resource in the plain for environment/other uses.