A meta-analysis to explore the impact of straw decomposing microorganism inoculant-amended straw on soil organic carbon stocks

Although the application of straw decomposing microorganism inoculants (SDMI) can accelerate straw decomposition, the underlying mechanisms affecting soil organic carbon (SOC) under different scenarios remain unclear. We conducted a meta-analysis using 226 observations from 86 studies on SOC changes under straw return with or without SDMI applications. Overall, our results indicated that straw with SDMI application increased the SOC stock by 1.51% at an initial carbon-to-nitrogen ratio (ICNR)>25 (P<0.05), while the effect of ICNR≤25 was insignificant. In particular, at ICNR>25, application of SDMI-treated straw increased SOC stocks in northern temperate continental areas (NTC) higher than in subtropical monsoon regions (STM). Furthermore, the straw with SDMI application increased higher SOC stocks in soils with pH>7.5 than those with pH≤7.5. In terms of agricultural management practices, SOC stocks were significantly higher in straw buried (SB), the experimental duration of straw return (EDSR)≥1 year, the straw return amount (SRA)>6,000 kg ha^–1, and the SDMI application rate (SDMIR)>30 kg ha^–1 conditions. The effect of straw with SDMI on SOC stocks under straw burying (SB) was significantly higher than that under straw mulching (SM) at ICNR≤25. At ICNR>25, EDSR, SDMIR, and the mean annual precipitation (MAP) were the main drivers of the effect of SDMI addition to straw on SOC stocks. Straw with SDMI induced SOC stock increases which increased with EDSR and decreased with increasing MAP. These findings provide a scientific basis for decision-makers and stakeholders to improve soil C management via the application of SDMI-amended straw at both regional and large scales.