Soil nitrogen availability mediates the positive effects of intercropping on soil organic carbon at global scales

Intercropping is an effective cultivation practice to develop sustainable agroecosystems and increase soil organic carbon (SOC) and nitrogen (N) with rich crop diversity. With increased duration, the changes in soil N availability might affect microbial and plant growth and consequently regulate the intercropping effects on SOC sequestration. However, the response of intercropping effects on SOC components to soil N availability has been poorly explored. In this study, we constructed a global database with 939 paired data (intercropping vs. monoculture) from 60 publications. We found that intercropping increased SOC (by 7.94%), microbial biomass carbon (MBC, by 23.73%), particulate organic carbon (POC, by 23.27%), and dissolved organic carbon (DOC, by 16.46%) compared to monoculture. The intercropping effects (percentage change, %) on SOC content strongly depends on soil N availability (soil C: N) and the interactions with duration and crop types. In N -limited soils (soil C: N > 15), intercropping increased SOC and POC contents by 14% and 31%, respectively, which were 2-3 times higher than those in N -rich soils (soil C: N < 15). It implies higher intercropping effects in more N -limited soils. In addition, intercropping increased MBC:SOC by 63% in N -limited but not in N -rich soils, indicating greater contributions of microbial -derived C to SOC storage in N -limited but not in N -rich soils. This might be attributed to that the stimulated microbial decomposition of soil organic matter counterbalanced the microbial -derived C accumulation in N -rich soils. Taken together, these results indicate that soil N availability regulates the intercropping effects on SOC content and the contributions of microbial -derived C to SOC storage. Overall, these findings highlight the importance of soil N availability on SOC content with intercropping, implying that intercropping is a suitable agricultural approach especially in N -limited soils and nutrient management should be carefully considered in long-term intercropping experiments.