Methane Emission Reductions from the Alternate Wetting and Drying of Rice Fields Detected Using the Eddy Covariance Method.

Rice cultivation contributes 11% of the global 308 Tg CH4 anthropogenic emissions. The alternate wetting and drying (AWD) irrigation practice can conserve water while reducing CH4 emissions through the deliberate, periodic introduction of aerobic soil conditions. This paper is the first to measure the impact of AWD on rice field CH4 emissions using the eddy covariance (EC) method. This method provides continuous, direct observations over a larger footprint than in previous chamber-based approaches. Seasonal CH4 emissions from a pair of adjacent, production-sized rice fields under delayed flood (DF) and AWD irrigation were compared from 2015 to 2017. Across the 2 fields and 3 years, cumulative CH4 emissions in the production season were in the range of 7.1 to 31.7 kg CH4-C ha-1 for the AWD treatment and in the range of 75.7-141.6 kg CH4-C ha-1 for the DF treatments. Correcting for field-to-field differences in CH4 production, the AWD practice reduced seasonal CH4 emissions by 64.5 ± 2.5%. The AWD practice is increasingly implemented for water conservation in the mid-south region of the United States; however, based on this study, it also has great potential for reducing CH4 emissions.