A fertilizer and fertilization technology innovation team from Institute of Agricultural Resources and Regional Planning (IARRP) at the Chinese Academy of Agricultural Sciences, recently uncovered a special microbial mechanism. They found that delayed flooding, after the incorporation of green manure, enhances the formation and stabilization of microbial residues in paddy soil. The findings were published in the prestigious UK-based academic journal Soil Biology and Biochemistry.

Microorganisms play a crucial role in regulating soil organic carbon or SOC cycling through the decomposition of organic matter and the formation of microbial residues — with the latter being a key source of stable SOC. Incorporating green manure provides microorganisms with easily decomposable substrates and promotes residue formation. However, in paddy fields, this process is influenced by the redox environment resulting from flooding. While continuous flooding can suppress the mineralization of some SOC, it also limits microbial growth and the accumulation of residues, and increases CH4 emissions. A brief aerobic phase might accelerate the decomposition of green manure and microbial assimilation, but it could also trigger the priming loss of native SOC. Research indicates that optimizing water management after green manure incorporation to enhance soil carbon sequestration, while minimizing greenhouse gas emissions, remains a critical area of study.

In the study, the 13C-labeled Astragalus sinicus was used in a microcosm incubation experiment. By employing CO2 and CH4 isotope tracing, microbial residue carbon analysis, and metagenomics, the study revealed that a "short-term aerobic followed by anaerobic" environment — created by delaying flooding for five days after green manure incorporation — promoted early decomposition of Astragalus sinicus and microbial carbon assimilation. This significantly increased the accumulation of fungal residue carbon and the efficiency of microbial residue formation, while reducing the potential for subsequent microbial decomposition of residues. Compared to immediate flooding, delaying flooding was found to have reduced CH4 emissions from Astragalus sinicus by 96.6% and decreased the CO2 and CH4 mediated priming effects by 12.4% and 97.1%, respectively. This resulted in an overall priming effect reduction of 29.9%. Moreover, the study demonstrated that the dry tillage and wet soaking technique can synergistically enhance paddy soil carbon sequestration and reduce greenhouse gas emissions. That's by promoting the conversion of green manure carbon into microbial residues and inhibiting their subsequent decomposition.

Mechanisms underlying the promotion of microbial necromass formation and stabilization in paddy soil by delayed flooding green manure incorporation.

Path analysis model of the effects of water management on the formation and priming effect of microbial residues

Assistant researcher Ma Zhengbo from the Institute of Agricultural Environment and Resources, at the Yunnan Academy of Agricultural Sciences, is the first author of the paper. Professor Zhou Guopeng from the College of Resources and Environment, at Anhui Agricultural University, and researcher Cao Weidong from the IARRP, are the corresponding authors. The research was supported by several projects, including the national key laboratory of efficient utilization of arid and semi-arid farmland in northern China, and also, the National Natural Science Foundation of China (32573148, 32202609), the National Key R&D Program under the 14th Five-Year Plan (2021-2025) (2021YFD1700200, 2023YFD1901204), and the National Green Manure Industry Technology System (CARS-22).

Citation: 

Ma Z, Chang D, Ma Q, Fu H, Sun J, Liang T, Cai C, Tang S, Zhou G, Jones D L, Wanek W, Zhang Q, Zhu H, Cao W. 2026. Delayed flooding after green manure incorporation enhances microbial necromass formation and stabilization in paddy soils. Soil Biology and Biochemistry, 223: 110297.

Link: https://doi.org/10.1016/j.soilbio.2026.110297