Edaphic Factors and Fertilization Practices Jointly Regulate Microbial Necromass Contribution to Soil Organic Carbon in Global Croplands

ABSTRACT Effectively managing soil organic carbon (SOC) for soil quality and climate mitigation requires a mechanistic understanding of its stabilization pathways. Microbial necromass carbon (MNC), a major source of persistent SOC, is influenced by climate, soil properties, and agricultural management. However, how these factors jointly shape the contribution of MNC to SOC (MNC/SOC) at a global scale remains largely unknown. Here, we synthesized a global dataset comprising 636 observations from 60 peer‐reviewed articles on cropland topsoils to identify the dominant drivers of MNC/SOC and provide actionable insights for its management. The average MNC/SOC in global croplands was 0.47 ± 0.19. Our analysis indicated that soil clay content and the C/N ratio were the primary regulators of MNC/SOC; specifically, clay content showed a positive correlation, while the C/N ratio exhibited a negative correlation. Furthermore, we found that fertilizer type, rather than application rate, emerged as the key lever controlling the MNC/SOC. Compared to mineral fertilization, organic fertilization significantly increased 27% of MNC/SOC, mainly resulting from the amplified positive effect of clay and reduced negative impact of soil C/N ratio. Global modeling further indicated that organic fertilization was the superior strategy for enhancing MNC/SOC across the majority of global croplands, particularly in clay‐rich regions, whereas mineral fertilizers may be more effective in a few arid regions. Collectively, these findings demonstrate that prioritizing organic fertilization can effectively leverage positive clay interactions and mitigate C/N stoichiometric constraints, offering a globally effective strategy to strengthen the microbial pathway of soil carbon stabilization and combat land degradation.