Cascading Effects of Irrigation Regimes on Soil Microenvironment, Rice Physiology, Crop Production, and Environmental Outcomes

Rice irrigation management influences soil conditions, crop physiology, productivity, and environmental outcomes, but the links among these responses remain incompletely understood. This review critically integrates evidence on continuous flooding (CF), alternate wetting and drying (AWD), controlled irrigation (CI), saturated soil irrigation (SSI), and rainfed supplementary irrigation (RAI) within a soil–root–canopy–production–environment framework. Changes in soil moisture and redox conditions affect nutrient and potentially toxic element availability, root development, canopy photosynthesis, and assimilate allocation, thereby influencing grain yield and quality. Under moderate, appropriately timed water-saving irrigation, selected studies report 10–35% reductions in irrigation water input while maintaining or increasing yield and improving water use efficiency (WUE). However, responses vary with drying intensity and timing, cultivar, soil, and climate; severe deficits can reduce yield and impair grain quality. Coordinated water–nitrogen management may improve partial factor productivity of nitrogen (PFPN) and internal nitrogen-use efficiency (IE), although responses vary. AWD generally reduces methane (CH4) emissions but may increase nitrous oxide (N2O) emissions and cadmium availability; net global warming potential (GWP) and greenhouse gas intensity (GHGI) depend on site-specific conditions. Future research should prioritize validated irrigation thresholds, long-term monitoring, and integrated management of productivity, resource efficiency, greenhouse gases, and grain safety.