Unexpected high reduction of methane emission via short-term aerobic pre-digestion of green manured soils before flooding in rice paddy

•Biomass application as green manure increased CH4 emission by 5.8 times over chemical fertilization (NPK).•More than 10 days of aerobic pre-digestion of biomass amended soil before flooding decreased over 60% of seasonal CH4 flux.•Short-term aerobic pre-digestion of biomass amended soil did not change rice productivity.•More than 10 days of aerobic pre-digestion reduced more than 60% of CH4 flux intensity (kg CH4 kg−1 grain).