Climate-smart water management in rice paddies: a meta-synthesis on greenhouse gas emissions and yield impacts
Kazunori Minamikawa
Abstract
Abstract Water management practices in rice paddies, particularly alternate wetting and drying and midseason drainage followed by intermittent irrigation, are widely recognized for reducing methane (CH 4 ) emissions and irrigation water use compared to continuous flooding (CF). However, these practices also increase nitrous oxide (N 2 O) emissions and their effect on rice yield remains unclear, especially in the context of technology dissemination to farmers. This study (1) reviews 11 recent meta-analyses on CH 4 and N 2 O emissions and rice yield and (2) synthesizes their reported effects on rice growth and yield. Aggregated data show that CH 4 emissions decreased by 31–62% ( n = 10), while N 2 O emissions increased by 37–445% ( n = 7), relative to CF. Rice yield change ranged from − 5.4% to + 11% with a mean of + 1.3% ( n = 8). The impact of water management on rice yield varied depending on the timing and intensity of drainage events, with excessive water stress—particularly during the heading stage—and prolonged reductive soil conditions being key risk factors. Results indicate that mild-intensity drainage practices, such as ‘safe AWD,’ not only avoid yield penalties but can significantly enhance rice productivity when tailored to favorable environmental and agronomic conditions. For effective dissemination of these practices, leveraging yield improvement as an incentive for farmers is essential. Optimizing drainage schedules in accordance with rice physiological stages and local conditions is critical. With appropriate localization, water management can serve as a climate-smart strategy that simultaneously improves water efficiency, reduces greenhouse gas emissions, and maintains or increases rice productivity.