Rice Genomics and Genetics 2025, Vol.16, No.5, 254-259 http://cropscipublisher.com/index.php/rgg 257 al., 2015). Similarly, in a study from Indonesia, rice grown under AWD with water media and rice husk showed the highest plant height and number of stems, indicating a positive impact on vegetative growth (Damanhuri et al., 2022). These findings suggest that AWD can enhance certain growth parameters, potentially leading to more robust plant development. 5.2 Dry matter accumulation and photosynthetic response AWD irrigation can influence dry matter accumulation and photosynthetic efficiency in rice plants. The method has been associated with increased root activity, which can enhance nutrient uptake and photosynthetic response (Song et al., 2020). This is supported by findings from a meta-analysis indicating that AWD can maintain or even improve photosynthetic efficiency under certain conditions, despite reduced water inputs (Carrijo et al., 2017). The increased root activity under AWD may contribute to better dry matter accumulation, supporting overall plant growth and yield. 5.3 Yield components The impact of AWD on yield components such as panicle number, grain weight, and seed setting rate varies across studies. In Nepal, AWD did not significantly affect yield components in one rice cultivar, while in another, a decrease in filled grain number was offset by an increase in effective tillers per hill (Howell et al., 2015). In Bangladesh, AWD treatments resulted in slightly lower grain yields compared to continuous flooding, but with improved water use efficiency. In contrast, a study in Tamil Nadu, India, reported higher yields under AWD compared to conventional methods, highlighting the potential for AWD to enhance yield components under specific conditions. These findings indicate that while AWD can reduce water use, its effects on yield components can vary depending on local conditions and rice varieties. 6 Environmental and Soil Health Impacts 6.1 Soil redox conditions and microbial activity Alternate wetting and drying (AWD) irrigation significantly influences soil redox conditions and microbial activity. AWD alters the soil's redox potential, which can enhance microbial diversity and activity, leading to improved nutrient bioavailability. Studies have shown that AWD increases the total concentration and bioavailability of essential nutrients such as nitrogen, phosphorus, and potassium by 16%-54% compared to continuous flooding (CF) systems. This is attributed to the dynamic changes in soil moisture and redox conditions that favor microbial processes, enhancing nutrient cycling and availability. The presence of diverse microbial communities, including Bacillus and Pseudomonas species, is more pronounced under AWD, contributing to better nutrient modulation and plant growth (Majumdar et al., 2023). 6.2 GHG emission dynamics (methane and nitrous oxide) AWD irrigation has a complex impact on greenhouse gas (GHG) emissions, particularly methane (CH4) and nitrous oxide (N2O). AWD significantly reduces CH4 emissions by 47%-51.6% compared to CF, due to the intermittent drying periods that limit anaerobic conditions favorable for methanogenesis (Ishfaq et al., 2020). However, this reduction in CH4 is often accompanied by an increase in N2O emissions, ranging from 44% to 280%, as the aerobic conditions during drying phases promote nitrification and denitrification processes (Liao et al., 2020; Zhao et al., 2024). Despite the increase in N2O emissions, the overall global warming potential (GWP) is reduced under AWD due to the substantial decrease in CH4 emissions (Gao et al., 2024). 6.3 Soil structure and organic matter retention AWD irrigation can positively affect soil structure and organic matter retention. The practice of AWD helps maintain or even improve soil organic carbon (SOC) levels, which are crucial for soil health and structure. Studies indicate that maintaining SOC levels above 12 g/kg is beneficial for minimizing yield losses and enhancing soil structure under AWD conditions (Gao et al., 2024). Additionally, AWD can improve soil aggregation and porosity, which are essential for root growth and water infiltration, thereby supporting sustainable rice production (Zhang et al., 202). The dynamic wetting and drying cycles in AWD promote the retention of organic matter, which is vital for long-term soil fertility and productivity.
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