The effect of winter crop incorporation on greenhouse gas emissions from double rice-green manure rotation in South China.

Chemical fertilizer plays a vital role in increasing crop yield. However, the environmental risk and the adverse effect on soil caused by excessive chemical fertilizer can be mitigated by using organic fertilizer (green manure Chinese milk vetch) and straw returning. Therefore, this field study was conducted to determine the impact of winter crop incorporation with mineral fertilizers on methane (CH4) and nitrous oxide (N2O) emissions and the related genes (mcrA, pmoA, AOA, AOB, nirS, nirK, and nosZ) as well as the relationship among greenhouse gas (GHG) emissions, related genes, and soil properties. The study comprised winter crop incorporation with mineral fertilizer at the reduced rate of 0% (MRN1), 12.5% (MRN2), and 25% (MRN3). The results indicated that the early and late rice yield from treatments MRN2 and MRN3 increased by 25% and 4% compared with control CK (winter fallow, without green manure incorporation, and conventional nitrogen fertilizer amount). CH4 annual cumulative emission increased by 34% resulting from increased abundance of mcrA genes of methanogens. Furthermore, N2O annual cumulative emission increased due to soil microbial biomass nitrogen, AOA (amoA), AOB(amoA), nirK, and nirS abundance. The global warming potential (GWP) increased by 34%; however, there was no significant difference on the GHGI from all the treatments resulting from the increased yield. Therefore, winter crop incorporation with different rate of reduced mineral fertilizer significantly increased the crop yield and increased the SOC and MBC content. Meanwhile, winter crop incorporation increased CH4 and N2O annual cumulative emission mainly resulting from the increased abundance of mcrA genes of methanogens, soil microbial biomass nitrogen, AOA(amoA), AOB(amoA), nosZ, nirK, and nirS abundance.