Delayed flooding after green manure incorporation decreases methane emissions and greenhouse gas intensity in green manure-double rice paddy fields

Water management is one of the most important practices that regulates soil carbon sequestration and greenhouse gas reduction in green manure-double-cropping rice fields. However, research to identify a reasonable water management approaches and the responses of methanogenic and methanotrophic communities to water management is crucial. Herein, 2-years field and microcosm experiments were arranged to investigate the effect and mechanisms of delayed flooding after co-utilizing green manure and rice straw on greenhouse gas emissions (especially methane ). The field experiment had the following six treatments: no residue (CK), where no green manure retained; water management treatment at 0, 2, 5, 10 and 15 days after co-utilizing green manure and rice straw (i.e., 0DbF, 2DbF, 5DbF, 10DbF and 15DbF). The microcosm experiment comprised two treatments: 0DbF and 10DbF. Compared with the CK, the co-utilizing green manure and rice straw could effectively increase rice yield but increases CH4 emissions. However, the 10DbF treatment significantly reduced CH4 emissions, GWP, GHGI and Yield-scaled CF compared to the 0DbF. Furthermore, the 10DbF treatment inhibited C availability of methanogens through reducing DOC concentrations of surface water, thereby reducing CH4 emissions during the rice growth season.