Crop diversification promotes soil aggregation and carbon accumulation in global agroecosystems: A meta-analysis

Soil aggregation contributes to the stability of soil structure and the sequestration of soil organic carbon (SOC), making it an important indicator of soil health in agroecosystems. Crop diversification is considered a rational management practice for promoting sustainable agriculture. However, the complexity of cropping systems and crop species across different regions limits our comprehensive understanding of soil aggregation and associated carbon (C) content under crop diversification. Therefore, we conducted a meta-analysis by integrating 1924 observations from three diversification strategies (cover crops, crop rotation, and intercropping) in global agroecosystems to explore the effects of crop diversification on soil aggregates and associated C content. The results showed that compared to monoculture, crop diversification significantly increased the mean weight diameter and bulk soil C by 7.5% and 3.3%, respectively. Furthermore, there was a significant increase in the proportion of macroaggregates and their associated C content by 5.0% and 12.5%, while there was a significant decrease in the proportion of microaggregates as well as silt-clay fractions along with their associated C under crop diversification. Through further analysis, we identified several important factors that influence changes in soil aggregation and C content induced by crop diversification including climatic conditions, soil properties, crop species, and agronomic practices at the experimental sites. Interestingly, no significant differences were found among the three cropping systems (cover crops, crop rotation, and intercropping), while the effects induced by crop diversifications showed relatively consistent results for monoculture crops as well as additive crops and crop diversity. Moreover, the impact of crop diversification on soil aggregates and associated C content is influenced by soil properties such as pH and SOC. In general, our findings demonstrate that crop diversification promotes soil aggregation and enhances SOC levels in agroecosystems worldwide.