Field Crop 2025, Vol.8, No.3, 154-165 http://cropscipublisher.com/index.php/fc 157 reduction in yield. In fact, due to a better population structure and higher nutrient utilization, it can even slightly increase yield (Shaibu et al., 2014). 3.3 Summary of yield results from field trials and large-scale promotion Indeed, many experiments and field demonstrations have shown that the AWD irrigation method does not affect the yield. Whether in the Philippines, Bangladesh or China, farmers have actually found that the yield is about the same as that of those who have been constantly flooded. Sometimes, due to less lodging and diseases, the yield can even be slightly higher (Hossain and Islam, 2022). Of course, the results may fluctuate a little depending on the region and year, but in most cases, the output variation is within 5%, which is not very significant. In some places, even when AWD is used in combination with soil improvement measures, the output can be further increased (Neogi et al., 2018). Although in particularly dry and hot years, improper operation may affect the formation of ears, it can generally be avoided by adjusting management. Overall, as long as the water pipes are used reasonably, AWD basically will not cause a reduction in rice yield. At the same time, it can save water, reduce emissions, and has good stability. This also makes farmers more willing to accept it. After all, they don't have to worry about a significant drop in harvest, and it will be easier to promote. 4 The Impact of AWD on Greenhouse Gas Emissions 4.1 Sources and dynamics of major greenhouse gases (CH₄, N₂O, CO₂) in rice fields Rice fields are actually a major source of greenhouse gases, among which methane and nitrous oxide are the most troublesome. You may not know that if the field is constantly flooded and the soil is deprived of oxygen, methanogenic bacteria will be particularly active, and methane will be discharged through soil pores and rice plants-usually most obviously during the peak tillering period and the later stage of heading. If the fields are dried in the middle, the discharge will temporarily stop, but once water is reapplied, it may rebound. Nitrous oxide is quite different. It is related to the nitrification and denitrification processes. It hardly occurs when the water is constantly flooded. Instead, it tends to suddenly peak when the water dries up or when the water and soil alternate (Jiang et al., 2014; Chidthaisong et al., 2018). As for carbon dioxide, although it does exist, its cycle is short and its impact is small. What people are more concerned about are still methane and nitrous oxide. Overall, fields that have been constantly flooded emit more methane and have a stronger greenhouse effect. Although the alternation of dry and wet conditions may cause a slight increase in nitrous oxide, it leads to a greater reduction in methane, and the overall warming potential actually decreases. So, irrigation methods like AWD, by adjusting water content, are indeed an effective way to control rice field emissions and mitigate climate impacts. 4.2 The mechanism of AWD in reducing methane (CH₄) emissions When it comes to greenhouse gases in rice fields, one of the most obvious advantages of (alternating dry and wet irrigation) AWD is that it can significantly reduce methane emissions. This is mainly because AWD makes the fields sometimes dry and sometimes wet. When the soil is dry and there is oxygen, methanogens are less active-they prefer an environment that is constantly flooded. Meanwhile, aerobic conditions can also promote the oxidation of methane, allowing some of the methane that has already been produced to be consumed. Actual field data shows that after the application of AWD, methane emissions throughout the growing season can be reduced by 30% to 70%, and in some areas, it can even reach 90% (Karki et al., 2022; Zhao et al., 2024). Of course, this effect is related to the duration and frequency of drying. Generally speaking, the longer and more frequently it is dried, the more obvious the reduction in emissions will be. However, on the other hand, when operating, one should not only focus on reducing emissions but also ensure that the rice gets enough water. If it is too dry, the yield may be affected. Overall, AWD can significantly reduce methane emissions with little impact on yield, greatly improving the carbon efficiency of rice cultivation. It can be regarded as a practical approach towards low-carbon agriculture. 4.3 Potential impact on nitrous oxide (N₂O) emissions and trade-off relationship Unlike the significant reduction of methane, the emissions of nitrous oxide (N₂O) are often higher under AWD. This is mainly because the alternation of dry and wet conditions activates the nitrification and denitrification process in the soil, causing some nitrogen fertilizers to escape in the form of N₂O. The fields that have been
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