Physio-ecological regulating mechanisms for highly efficient water use of crops

The North China Plain (NCP) is a severe water shortage region and one of the important grain crop production bases in China. With the rapid rise of China's national economy, the water shortage of agriculture production has acutely increased. To reduce the exploitation of groundwater and resolves problems in agricultural water resources, a series of water-saving measures have been proposed and developed. However, improving crop water use efficiency has been among the most basic requirements to this goal. This paper therefore reviewed four aspects of research progresses of improving crop water use efficiency. They included the varieties difference in high water use, response difference of crops at different growth stages to water, regulation of stomatal conductance on excessive transpiration of crop leaves, differences in physio-ecological strategies of different drought-resistant corps to water stress. On this base, three integrated cultivation techniques were advanced according to our research results. The first was adjustment of planting structure to improve annual water use efficiency of crops. To gain this goal, it was important to establish rational planting structures and rotation patterns based on difference in water consumption characterizes, yield and economic efficiency of crops/varieties. In the high-yield region of the piedmont of Mountain Taihang, the pattern of three-cropping in two years of winter wheat-summer millet/spring sweet potato was a planting structure with high yield-and economic-water use efficiencies. The second cultivation technique was activation and broadening of sowing date thresholds via increase seeding rate and mulching to increase rainwater use efficiency. In our research, grain yield of winter wheat was not significantly different regarding sowing date-before December or in early October under intensive seeding and soil-coated film mulching in the Bohai Lowland Plain. The third aspect was improving crop water use efficiency in rain-fed fields by coating soils with film mulch. The pattern of subsoil plastic film mulch dual used by winter wheat and summer maize significantly inhibited soil evaporation and salt accumulation, increased seed emergence rate, promoted aboveground biomass and increased grain yield and water use efficiency of two crops in dry lands. In the Bohai Lowland Plain, this cropping pattern made use of rainwater and slight saline water. Grain yield of winter wheat-summer maize was up to 15 910-16 966 kg·hm^-2, which represented an increase of 10.52%-41.44% over that under no mulching. In the future, disruptive innovations such as new quantitative standards for high crop water use efficiency and utilization of unconventional water resources can lead to significant breakthroughs in agricultural water saving.