Field Crop 2025, Vol.8, No.3, 154-165 http://cropscipublisher.com/index.php/fc 155 (Chidthaisong et al., 2018). Therefore, AWD is regarded as a key technology for water conservation and emission reduction. Countries like China and the Philippines are promoting it. However, due to the different conditions in various regions, the specific effects still need further research. Given the potential of AWD in water conservation and emission reduction and the complexity of its application, this study aims to systematically review its impact on rice yield and greenhouse gas emissions from paddy fields. Based on field experiments and promotion experiences, this article explores the applicability and limitations of AWD in different ecological and management scenarios. The analysis focuses on its basic principles and operation methods, as well as the differences from traditional irrigation. It explains the mechanisms of action on root growth, nutrient absorption, photosynthesis and yield composition, assesses the dynamic emissions of CH₄ and N₂O in paddy fields and the trade-off relationship between methane reduction and nitrous oxide increase (Loaiza et al., 2024), and discusses its impacts on soil properties, water resource utilization and the ecological environment (Echegaray-Cabrera et al., 2024). Meanwhile, the research focuses on the economic benefits of AWD, farmers' willingness to adopt it and the obstacles to its promotion. It proposes application strategies by combining policies and international experiences, and draws on typical empirical studies in Southeast Asia to summarize regional promotion experiences. Finally, we look forward to its challenges in different ecological zones and the prospects of synergy with other low-carbon technologies, with the aim of providing a scientific basis for optimizing the irrigation system and achieving green production increase. 2 The principle and Implementation of Alternating Irrigation (AWD) 2.1 Basic concepts and operational methods of AWD Alternating wet and dry irrigation (AWD), in essence, means no longer keeping the rice fields flooded all the time. Instead, it involves draining the water and then refilling it, alternating this process. Generally, when the seedlings are still small at the beginning, a little shallow water is maintained. Once they stabilize, the water is allowed to fall slowly until it is about 15 centimeters lower than the field surface-this is the "Safe AWD" standard recommended by the International Rice Research Institute (Mote et al., 2021). At this point, if water is applied, it is less likely that the rice will suffer from drought. Of course, it depends on the period: during the tillering stage, it should not be too dry, otherwise it will affect the division. By the time of panicle formation and heading, if it is too dry, there will be fewer grains produced. Overall, however, through this cycle of "shallow water-drying-rewatering", AWD can indeed save water and the output is not likely to drop much (Chu et al., 2016). The soil is sometimes dry and sometimes wet, but it is more breathable, and the root system and microorganisms are also more active. Nowadays, there are also mild and severe AWD types. Generally, mild AWD has almost no impact on yield, but when operating, it is still necessary to consider the location, weather, and even the variety to select the appropriate standard. 2.2 Comparison with traditional irrigation methods Compared with continuous flooding, AWD shows differences in soil moisture, nutrient cycling and ecological processes, thereby affecting the paddy field environment and crop performance. Studies show that AWD can reduce irrigation water by approximately 20% to 30%, saving 1 000 to 1 500 tons per hectare and significantly improving water use efficiency. However, continuous flooding leads to low efficiency due to seepage and evaporation. In terms of the soil environment, continuous flooding keeps the soil anaerobic for a long time, which is conducive to methane production. AWD increases the REDOX potential through periodic drying, inhibits methane production and promotes nitrification. For crops, although continuous flooding provides stable moisture, it is prone to restricting root development due to oxygen deficiency. Moderate AWD promotes root penetration and enhances vitality without affecting the growth of the above-ground parts. Multiple experiments have shown that the output of AWD is not significantly different from that of continuous flooding, with an average reduction of only about 3%. If not managed properly, it may lead to a reduction in production. Moderate alternation of dry and wet conditions during the tillering stage is conducive to nutrient absorption, while during the heading and flowering stage, it is necessary to maintain moisture to prevent a decrease in seed setting rate. Overall, the rational implementation of AWD can not only save water but also stabilize yields, providing a feasible approach for rice-growing areas to alleviate water resource pressure and reduce emissions.
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