Field Crop 2025, Vol.8, No.3, 154-165 http://cropscipublisher.com/index.php/fc 158 constantly flooded actually have very low N₂O emissions due to lack of oxygen. However, during the process of AWD drying up and rewatering, the soil is alternately rich in oxygen and deficient in oxygen, which makes it easy for a peak in N₂O emissions to occur at this time. Overall, the total amount of N₂O in AWD fields is indeed higher than that of continuous flooding, but its absolute amount is much smaller than that of methane. The increase in N₂O is far from offset by the reduction in methane, so the overall greenhouse effect is still reduced. However, it should also be noted that if too much nitrogen fertilizer is used or the dry and wet alternations are too frequent, the peak value of N₂O may be particularly high. To control this risk, it is best to optimize nitrogen fertilizer management, such as applying less fertilizer, using slow-release fertilizer or adding some nitrification inhibitors, and at the same time, prevent the fields from being too dry. In fact, as long as water and fertilizer are well combined, AWD can not only reduce methane but also control N₂ O. In most cases, the overall emission reduction effect is better than continuous flooding. It can be regarded as a practical emission reduction method (Abid et al., 2019; Wang et al., 2025). Figure 1 Schematic diagram of whole study plan (Adopted from Abid et al., 2019) 5 Ecological and Environmental Effects 5.1 The influence of AWD on the physical and chemical properties of soil A change in irrigation methods not only affects greenhouse gases and crops, but also makes the soil itself different. Take AWD for example. The field is dry and wet, and the soil repeatedly shrinks and expands, undergoes oxidation and reduction, which actually makes the structure more stable and breathable, reduces the bulk density, and some cracks may appear-this is actually beneficial for the root system to grow deeper, and the entire plough layer will also be looser. In terms of chemical properties, AWD reduces the accumulation of reducing substances such as ferrous and manganese, alleviates the toxicity to crops, and also promotes the conversion of ammonium nitrogen into nitrate nitrogen, enhancing the supply capacity of nitrogen. However, if not managed properly, nitrogen is also prone to loss. The activation of phosphorus under AWD is slightly lower, while potassium has little effect. In terms of microorganisms, AWD will make aerobic bacteria more active, accelerate the decomposition of organic matter, and increase the release of nutrients in the short term. However, in the long term, it may lead to a decrease in organic carbon (Islam et al., 2020). This can be compensated for by returning straw to the field. There is an advantage in terms of elements: AWD can reduce the arsenic content in rice, making it safer to eat, but it may slightly increase the activity of cadmium (Hu et al., 2023). Overall, AWD is mostly positive for soil structure and nutrient environment. However, it is best to combine it with fertilization and tillage measures, which can not only nourish the land but also reduce emissions.
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