Response of soil organic carbon fractions to legume incorporation into cropping system and the factors affecting it: A global meta-analysis

Recently, there has been increased advocacy for the adoption of rational cropping systems to increase soil organic carbon (SOC) levels and health and ensure food security. The intercropping and crop rotation of legumes with other crops is believed to improve soil environment and influence SOC dynamics. However, a comprehensive assessment of the effects of legume incorporation into cropping systems (LCS) on SOC fractions is still lacking. Therefore, this study aims to elucidate the effects of LCS on SOC fractions under different climatic conditions, soil properties, and agronomic practices, based on meta-analysis of 85 publications. LCS significantly increased the concentrations of microbial biomass carbon (MBC), dissolved organic carbon (DOC), particulate organic carbon, light fraction carbon (LFC), heavy fraction carbon, labile carbon pool, and recalcitrant carbon pool by 21.4 %, 7.2 %, 9.1 %, 29.6 %, 6.4 %, 7.1 %, and 7.9 %, respectively, compared with cropping systems without legume. LCS-induced increase in the contents of SOC fractions was stronger under relatively suitable climatic conditions (mean annual temperature > 15 °C, mean annual precipitation > 1000 mm, and aridity index (AI) > 0.65) and soils with more severe nutrient limitation (soil organic matter < 10 g kg −1 , pH < 6.6, and subsoils). Specifically, AI was positively correlated with the response ratios of labile organic carbon fractions, whereas initial soil pH was negatively correlated with MBC, DOC, and LFC. Additionally, low nitrogen fertilizer application rates (< 120 kg ha −1 ) and intercropping favored an increase in SOC fractions under legume cultivation. Overall, these results provide insights into the ecological benefits of legumes and highlights the importance of developing site-specific strategies to effectively manage SOC dynamics under legume cultivation for sustainable agricultural practices. • Legumes incorporation into cropping system (LCS) increased SOC fractions. • Response of SOC fractions to LCS varied with climatic and edaphic factors. • Lower N fertilizer and intercropping promoted LCS-induced increase in SOC stock. • Strategies development should consider legume growth and biological N fixation.