Organic amendments reshaped the chemical composition of soil organic matter: A meta-analysis

• Organic amendments increase aromatic carbon by 11% and soil organic carbon content by 52%. • Amendment nitrogen content is a key predictor of aromatic carbon formation. • Cold-wet climates and fertile-acidic soils created the most favorable conditions for accumulating aromatic carbon. • Climate-dependent efficacy of amendments in building soil C pools peaks under cool, wet conditions. Increasing soil organic matter (SOM) content is pivotal for soil health and climate change mitigation, yet the mechanisms governing long-term carbon (C) stabilization via organic amendments remains controversial. We performed a meta -analysis of 540 observations from 45 studies, analyzed by solid-state 13 C NMR spectroscopy, to evaluate the responses of SOM chemical composition and its driving factors to organic amendments. The dataset predominantly comprises cropland soils from Asia, under temperate and subtropical climates, with a focus on major soil types. Functional groups of SOM were associated with climate, soil, and amendment properties, identifying the key factors influencing C stabilization. Organic amendments increased aromatic C by 11%, driving a substantial 52% increase in SOC content compared with mineral-only fertilization. Organic amendment properties and climate factors explained 77% of SOC increase, with nitrogen (N) content identified as key predictors of aromatic groups. The most favorable conditions for aromatic C accumulation included high precipitation (>1000 mm), low temperature (20 g kg −1 ), total N (>1 g kg −1 ) contents, and acidic conditions (pH < 6), which are conditions that reflect slow decomposition rates and partial oxygen limitation. Our finding suggests that amendment strategies should account for both the intrinsic quality (e.g., C/N ratio) of the amendment and the extrinsic climatic conditions to optimize persistent C pool formation.