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

Abstract

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.