Non-Continuous Flooding Outperforms Continuous Flooding in Rice Fields Net Carbon Sequestration Despite Losses in Soil Organic Carbon Sequestration.

Rice feeds more than 50% of the global population with significant greenhouse gas (GHG) emissions. Non-continuous flooding (NCF) has been recognized as an effective practice for stabilizing rice yields, conserving water, and reducing GHG emissions from rice fields. However, the impacts of NCF on net carbon sequestration (NCS, defined as the total ecosystem GHG equivalent) in rice fields, including CH emissions, NO emissions, photosynthetic carbon sequestration linked to crop yield, and soil organic carbon (SOC) sequestration, have rarely been quantified comprehensively. This limitation hinders a complete understanding of the overall processes through which NCF affects NCS. This study conducted a meta-analysis of 1075 data pairs from 72 studies worldwide to quantify the effects of NCF on GHG equivalent components and its overall NCS benefits. Results showed that compared to continuous flooding (CF), NCF significantly increased the average NCS per growing season by 4615 kg CO-eq·ha (95% CIs: 468 to 8761, p = 0.031). Specifically, NCF significantly reduced CH emissions by 45.72% and significantly increased NO emissions by 35.77%, with an insignificant increase of 1.93% and 3.16% in CO emissions and yield, respectively. The ΔSOC (changes of SOC concentration before and after the growing season) significantly decreased with the mean difference effect size of -0.36 (95% CIs: -0.70 to -0.02), indicating smaller SOC changes for NCF. Meta-regression and random forest importance analyses were used to explore the effects of climatic and soil properties and management practices on GHG equivalent components. Implementing controlled irrigation with appropriate limitation of total water input could achieve a win-win situation of enhancing rice yield while mitigating GWP and Y-GWP. This study further quantified the effects of NCF on all components of GHG equivalent and the NCS benefits in rice fields, providing guidance for irrigation management practices to achieve dual carbon goals.