Conventional tillage combined with residue removal reduces growing-season methane emissions in flooded paddy (Oryza sativa L. subsp. japonica Kato) fields

Paddy (Oryza sativa L. subsp. japonica Kato) fields are one of the largest anthropogenic methane (CH4) sources, owing to the lack of relatively long-term scientific monitoring for paddy fields, the effects of long-term tillage and residue management on growing-season CH4 emissions remain unclear. Therefore, four treatments of different farmland managements were established to investigate growing-season CH4 emission, i.e. conventional tillage with residue returning (CTR), conventional tillage with residue removal (CT), reduced tillage with residue returning (RTR) and reduced tillage with residue removal (RT). The investigation lasted for 12 years since 2008. In-situ measurements of CH4 emissions were performed during the growing season from 2018 to 2020. Meanwhile, soil redox potential (Eh), nitrogen content, organic carbon content, enzyme activity and microbial abundance were measured and analyzed. Four treatments differed significantly (p < 0.05) on growing-season CH4 emissions. The cumulative CH4 emissions were in the order of RTR > CTR > RT > CT. The methanogens abundance (mcrA copy numbers) and the abundance ratio of methanogens to methanotrophs (mcrA/pmoA copy number ratios) are two sensitive indicators for cumulative CH4, we found that cumulative CH4 increased while the two indicators increased. Another important finding was that cumulative CH4 is positively correlated with soil enzyme activities (including dehydrogenase, fluorescein diacetate, β-glucosidase and urease) and NH4+-N content, however, negatively correlated with NO3−-N content. Since long-term CT transformed above CH4-emission-related parameters to prevent CH4 emission, this study suggests that CT is the best choice for reducing growing-season CH4 emission in paddy fields.