The inhibitory effect of a water-saving irrigation regime on CH4 emission in Mollisols under straw incorporation for 5 consecutive years

Methane (CH4), as a important source of greenhouse gases from paddy ecosystem was overestimated under multi-year straw incorporation. However, how CH4 can be affected by multi-year straw incorporation under different water-saving techniques is little known. In this study, the effects of straw incorporation years and irrigation regime on CH4 emission and its potential mechanism in Mollisols were investigated by conducting a multi-year in-situ experiment. The following 4 treatments were included: controlled irrigation + straw incor-poration for 1 year (C1), controlled irrigation + straw incorporation for 5 consecutive years (C5), flooded irri-gation + straw incorporation for 1 year (F1) and flooded irrigation + straw incorporation for 5 consecutive years (F5). Methane fluxes, soil microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), dissolved organic carbon (DOC), the relative abundance of methanogens and methanotrophs were determined. The results showed that straw incorporation for 5 consecutive years increased NH4+-N, NO3--N, DOC, MBC which led a increased in rice yield by 4.42-5.84% compared with 1 year straw incorporation. Controlled irrigation significantly reduced CH4 emission in Mollisols by 70.2-79.7% compared with flooded irrigation, and this reduction was more obvious under 5-year straw incorporation. The consequence of decreased CH4 emission was mainly affect by the decrease in DOC content. Another key reason of decreasing CH4 emissions under controlled irrigation was the relative abundance difference between methanogens and methanogens, which decreased from 266.7% to 19.3%. The present study provides a further detailed understanding of the CH4 emission mechanism for straw and irrigation management in Mollisols.

Automated summary

Through a multi-year in-situ experiment, it was found that consecutive five-year straw incorporation increased the content of NH4+-N, NO3--N, dissolved organic carbon (DOC), and soil microbial biomass carbon (MBC), resulting in a 4.42-5.84% increase in rice yield. Controlled irrigation significantly reduced CH4 emissions in Mollisols by 70.2-79.7%, and this reduction was more significant under five-year straw incorporation. The decrease in CH4 emissions under controlled irrigation was mainly due to the decrease in DOC content and the difference in relative abundance between methanogens and methanotrophs.