Research progress on the optimal allocation of agricultural irrigation water resources

The shortage of water resources is a key factor restricting the sustainable development of agriculture, and the optimal allocation of agricultural irrigation water resources is of great significance to guarantee food and water security. Based on the main types of optimal allocation models of agricultural irrigation water resources, the research progress on single crop irrigation optimal decision-making, multi-crop water and soil resources optimal allocation, and canal system water resources optimal operation were systematically reviewed. In the traditional single crop irrigation optimal decision-making, the maximum crop yield or economic benefit was usually selected as the optimization objective. With the improvement of people’s living standard, consumers pay more attention to crop quality. And the optimal decision-making of water-saving irrigation theory based on the response of water and quality for improving quality of crop has gradually become a research focus. The multi-crop water and soil resources optimal allocation mainly includes the adjustment of crop planting structure and allocation of irrigation water resources in the irrigation district, which has undergone a transformation from single objective to multiple objectives, structural optimization to spatial layout optimization, and only focusing on the improvement of crop yield to the water-energy-food-ecology collaborative optimization. According to the different optimization objectives, the canal system water resources optimal operation is usually divided into two categories. Firstly, the objective is to optimize the benefit indicators of irrigation district, such as crop yield, economic benefits, water fee income of the irrigation management department, and the utilization efficiency of water and soil resources. Secondly, the objective is to optimize the operation and management indexes of hydraulic engineering in irrigation districts, such as the least water loss during the canal operation, water delivery time, differences in the continuous water diversion time of each rotating irrigation group, water shortage, and smooth water flow transition. In addition, the main problems and future research plans in the optimal allocation model of agricultural irrigation water resources were pointed out. The study suggested that the optimal allocation model of irrigation water resources should be improved in the following four aspects: 1) Building more physiological crop water-quality models; 2) Achieving optimal allocation of irrigation water resources under the scenarios of climate change and human activities; 3) Building systematic optimal allocation model of irrigation water resources that fully consider canal systems, irrigation districts, crops, and growth stages; 4) Establishing irrigation optimization decision-making models with the objective of minimum soil evaporation; Overall, this review provides valuable information for domestic researchers.