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.