A Review on Multi-Process Movement of Water and Nutrients in Low-Pressure Sprinkler Irrigation and Related Crop Regulation Mechanisms

Low-pressure sprinkler irrigation combined with fertigation is a promising approach for sustainable agriculture. However, reducing operating pressure changes sprinkler hydraulic performance, droplet characteristics, and irrigation uniformity, which in turn affect droplet evaporation and drift, canopy interception, soil infiltration, and field microclimate, ultimately influencing crop growth and resource use efficiency. A systematic synthesis of these interconnected processes is currently missing. This review synthesizes current knowledge on low-pressure sprinkler irrigation by integrating findings from hydraulic engineering, soil physics, micro-meteorology, and crop physiology. It covers sprinkler hydraulic performance, water and nutrient transport, and crop response mechanisms. It also identifies priority directions for future research. Based on a critical evaluation of existing studies, several key findings emerge. For hydraulic performance, non-circular nozzles and flow dispersion devices can improve jet breakup and uniformity under low pressure. In particular, non-circular nozzles enhance jet instability and air entrainment via axis-switching, while water-dispersing needles and off-axis plate motion effectively improve near-sprinkler water distribution. For water and nutrient transport, low pressure increases droplet size and kinetic energy, reducing evaporation and drift losses. Canopy modifies throughfall droplets, affecting soil structure, infiltration and erosion. A notable finding is that soil water redistribution compensates for low irrigation uniformity, making root-zone soil water more uniform, whereas soil nitrogen uniformity remains close to the sprinkler irrigation uniformity. For crop responses, sprinkler irrigation improves microclimate (cooling and humidifying), enhances crop photosynthesis and reduces transpiration, thus increasing yield and water use efficiency. Importantly, reduced irrigation uniformity did not significantly reduce yield under the specific conditions reported in existing studies, benefit by lower losses and soil compensation. However, most existing microclimate studies are based on medium- and high-pressure systems; the response mechanisms under low-pressure conditions remain unclear. Future research should prioritize four areas, including long-term performance and economic feasibility of low-pressure sprinklers, coupled multi-process modelling of water and fertilizer transport and environmental risk assessment, field microclimate responses and crop physiological mechanisms under low pressure, and system regulation strategies tailored to different crops and regions. This review provides a holistic basis for optimizing water, energy, and fertilizer synergies in sprinkler irrigation.