Efficient utilization of various water sources in farmlands in the low plain nearby Bohai Sea

Freshwater shortage is a growing crisis in food production in the plain nearby the Bohai Sea. It is therefore important to efficiently utilize available water resources in the region, including fresh groundwater, brackish groundwater and precipitation during grain production season. This paper summarized the work of a 3-year field experiment at Nanpi Eco-Agricultural Experimental Station, Chinese Academy of Sciences on utilization of saline water in replace of fresh groundwater irrigation of winter wheat, deficit irrigation to reduce water use, high-performance cultivars, and the optimized planting and cultivation technologies in wheat-maize double cropping system. The results showed that jointing stage was critical for irrigation under a single irrigation application in winter wheat. Irrigation at jointing stage improved the growth of both aboveground and belowground parts of winter wheat. The enhanced root growth increased soil water utilization during late growth stages and also reduced the negative effects of water stress on yield under limited irrigation of winter wheat. The study also showed that the use of saline water with salt concentration less than 4 gL^-1 in place of freshwater irrigation at jointing stage of winter wheat did not affect yield, and prevented deep freshwater depletion. To mitigate the negative effects of soil salt in the top 20 cm soil profile after winter wheat harvest on successive crops (summer maize), about 70 mm of irrigation at sowing stage of maize was needed to support maize germination and seedling establishment. The results suggested that the return of the straw of both crops to the soil enhanced soil organic content. While the increased proportion of stable soil aggregates benefited the stability of soil structure, leaching of salt after saline irrigation improved during summer rainy season. The selection of better cultivars of winter wheat and summer maize had the potential to improve yield and water use efficiency by up to 20%. For summer maize, reducing inter-row spacing and increasing intra-row spacing improved the proportion of seedling establishment and interception ratio of solar radiation by crop canopy at seedling stage. This improved maize yield by about 10% compared with traditional planting. The combined results of the measures reduced freshwater use in irrigation, and significantly improved water use efficiency and grain yield of crops. The study showed that it was possible to maintain grain yield and to conserve fresh groundwater resources at the same time in the study area.