Rice cultivation contributes 11% of the global 308 Tg CH 4 anthropogenic emissions. The alternate wetting and drying (AWD) irrigation practice can conserve water while reducing CH 4 emissions through the deliberate, periodic introduction of aerobic soil conditions. This paper is the first to measure the impact of AWD on rice field CH 4 emissions using the eddy covariance (EC) method. This method provides continuous, direct observations over a larger footprint than in previous chamber-based approaches. Seasonal CH 4 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 CH 4 emissions in the production season were in the range of 7.1 to 31.7 kg CH 4 −C ha −1 for the AWD treatment and in the range of 75.7−141.6 kg CH 4 −C ha −1 for the DF treatments. Correcting for field-to-field differences in CH 4 production, the AWD practice reduced seasonal CH 4 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 CH 4 emissions.
Understanding methane (CH4) fluxes from rice (Oryza sativa L.) at the field scale is paramount to reducing environmental impacts while ensuring global food security. Greenhouse gas (GHG) measurements at the plot scale using static flux chambers (SFC) have long informed the understanding of flux dynamics and have largely been the basis of global flux estimates. However, in many parts of the world, the landscapes where agricultural fluxes are generated come from larger fields. Eddy covariance (EC) can measure trace gases on larger fields, but there are few studies available quantifying CH4 emissions under typical practices at a field scale. Furthermore, few of these studies are from the U.S. Midsouth, the largest producer of U.S. rice. This study compares and quantifies field‐scale SFC and EC flux measurements on a large commercial system in northeastern Arkansas during the 2015 and 2016 growing seasons, following typical producer practices. Daily measured SFC CH4 fluxes did not differ from EC‐daily CH4 fluxes (p = .108). Total season CH4 emissions, calculated as the sum of daily fluxes ranged from 50 to 156 kg CH4 ha−1 season−1, with SFC reporting greater emissions than EC. Although SFC and EC‐daily flux measurements were similar early (p = .382) and late (p = .543) in the season, they differed mid‐season (p < .001) with SFC consistently reporting greater fluxes than EC. The findings of this study help unify season long plot‐scale and field‐scale flux measurements and signify an advancement of our understanding of GHG fluxes from rice systems.
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