Greenhouse Gas Emissions and Global Warming Potential in Double-Cropping Rice Fields as Influenced by Two Water-Saving Irrigation Modes in South China

Abstract

“Thin-wet-dry” irrigation (TR) and alternate wetting and drying irrigation (DR) are two effective water-saving irrigation modes used for paddy fields. The objectives of this study were to assess the effects of two water-saving irrigation modes on methane (CH4) and nitrous oxide (N2O) emissions from rice fields in the south of the Tropic of Cancer, south China, and verify the hypothesis about the reducing effect of both TR and DR modes on global warming potential (GWP) and greenhouse gas emission intensity (GHGI) compared with conventional irrigation (CR). Three-year field experiments with three irrigation modes were continuously conducted during 2015–2017 to monitor the changes of CH4 and N2O fluxes during the growing period of double-cropping rice, and then the cumulative CH4 and N2O emissions, GWP, and GHGI were analyzed. Compared with CR mode, both TR and DR saved total irrigation amount by 19.5–40.4 and 27.1–52.5% but did not affect the rice yield; DR lowered CH4 emissions from double-cropping rice field over the whole growing period by 41.1–67.0% and TR only reduced CH4 emissions from 2016 late rice field by 31.4%, but TR and DR increased N2O emissions by 57–271 and 79–825%; DR lowered GWP and GHGI by 40.7–66.8 and 48.3–65.5%, and TR declined GWP and GHGI in 2015 and 2016 late rice fields by 31.3–43.4 and 22.4–49.7%. Moreover, rice season significantly influenced GWP and GHGI. Two water-saving irrigation modes reduced GWP and GHGI and our results can provide scientific basis in precisely estimating greenhouse gas emission in China.