Optimal drainage timing for mitigating methane emissions from rice paddy fields

Abstract

While rice production may need to increase to keep pace with the growing demand, efficient and sustainable management is needed to mitigate methane emissions from rice paddy fields, which still contribute substantially to the global methane budget. Field mid-season drainage is a popular water management strategy that reduces emissions by shortening the period of time the field spends in anaerobic conditions; however, it is still unclear how drainage timing affects its overall effectiveness. Here we combine observations from field experiments with a methane emission model to analyze how the time at which the field is drained controls the reduction in methane emissions. We show that an optimal drainage timing maximizes the mitigation efficiency of the drainage, defined as the reduction in methane emissions due to a mid-season drainage relative to the emissions in a continuous flooding management. We then estimate maximum mitigation efficiencies and optimal drainage timings across the experiments and shed light on the role of organic amendment. The average optimal drainage timing for organically amended fields is earlier than for non-amended ones (20 and 50 days after transplanting, respectively), promoting an average CH4 emissions reduction of about 45% and 35%, respectively. The potential increase in mitigation efficiency obtained by optimizing drainage timing highlights the important role of this strategy in a sustainable management of rice cultivation, where rice yield and N2O emissions may impose further constraints on water management.