Water use and water-saving irrigation in typical farmlands in the North China Plain

This paper summarized the researches of Center for Agricultural Resources Research, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences on water-saving irrigation for winter wheat and summer maize at the Luancheng Agro-Ecosystem Experimental Station, Chinese Academy of Sciences, a typical farming area in the North China Plain (NCP). The results from long-term field studies showed that for the period from 1980 to 2017, yield of winter wheat was increased by 55.7% and that of summer maize by 59.7% under fully irrigated conditions. Water consumption (ET) of winter wheat was increased from 400 mm to 465 mm, ET of summer maize was relative stable at about 375 mm. Annual ET was increased from 777.0 mm in the 1980s to 834.4 mm in the 2010s. The annual irrigation water demand was averagely around 300 mm. Therefore, it was necessary to reduce irrigation water use to conserve local groundwater resources. Under limited irrigation, one irrigation of winter wheat at jointing stage significantly increased vegetative and root growth of this crop, which was beneficial for the efficient use of soil water at later stages of crop growth. Under this critical stage irrigation schedule, annual ET was reduced by 165.2 mm, while grain production remained stable at relative higher level. Results also showed that by reducing irrigation amount per application and increasing irrigation frequency under limited irrigation, the combined effects of interaction of crop root, soil water and soil nutrient at the topsoil layer could increase water availability to the crop and thereby increase grain production and water use efficiency. A minimum irrigation (MI) schedule was developed for more serious water shortage regions, which was to maintain good soil moisture conditions at the time of sowing and no other irrigation being applied during the other growth periods. As compared with full irrigation, yield was reduced by 28%, but irrigation water use was reduced up to 69%, reduction in ET was by 43% and water use efficiency increased by 13%. Annual ET was reduced to 560 mm and annual irrigation water use was reduced to 120 mm. Significant reduction in irrigation water use was achieved as compared with the full irrigation schedule. As compared with the reduction in cropping intensity (RCI) measure (changing annual double cropping of winter wheat and summer maize to three crops every two years), MI schedule could fully use the rainfall resources and reduce soil evaporation consumption during fallow period under RCI. Yield of winter wheat and summer maize for MI under double cropping system was 5.5%-12.0% higher than that for RCI, with annual ET of 10%-13% less. Based on results from the long-term field experiment, the implementation of water-saving irrigation schedule such as MI and critical irrigation scheduling significantly reduced irrigation water use and at the same time maintained stable grain production. Therefore, water-saving irrigation schedule under double cropping of winter wheat and summer maize was recommended as one of the important measures for solving the problem in groundwater overdraft in the NCP.