Changes in soil microbial biomass, diversity, and activity with crop rotation in cropping systems: A global synthesis

Crop rotation is an environmentally friendly and highly sustainable cultivation method. Fully understanding the effects of crop rotation on soil microorganisms will facilitate the incorporation of this method. Despite the increasing number of studies exploring the effects of crop rotation on soil microorganisms, there has not been a comprehensive review of the relationship between crop rotation and soil microorganisms. A meta-analysis was conducted on 76 studies that reported the effects of crop rotation on soil microbial indicators. The eight most commonly used indicators were selected to estimate the effect of crop rotation on soil microorganisms. In terms of soil microbial biomass, crop rotation significantly increased soil microbial biomass carbon (MBC) and nitrogen (MBN) by 13.43 % and 15.84 % respectively, compared to those of continuous monoculture. A significant increase in the biomass of fungi was observed when other crops were introduced into continuous legume monoculture for rotation (45.50 %) and in regions where mean annual precipitation (MAP) values were 600 to 1000 (15.72 %). In terms of soil bacterial diversity, rotation increased Shannon's diversity index by 7.68 % when compared with monoculture practices. The effect of crop rotation on soil phosphatase and β-glucosidase activity was not significant in this analysis. Moreover, the effect sizes of crop rotation varied by management practices, such as monoculture crop type or tillage practices. Notably, rotation effects on MBC and MBN were more pronounced under conditions such as reduced tillage, introducing other crops into cereal monoculture for rotation, rotation containing legumes, mean annual temperature (MAT) > 8 °C or MAP 600–1000 mm. However, the opposite was true for Shannon's diversity index, and the rotation effect was more significant when no tillage or conventional tillage was applied, MAT < 8 °C, or MAP<600 mm. In conclusion, crop rotation increased soil MBC, MBN, fungal biomass and bacterial Shannon's diversity index when properly used with other agricultural practices. However, more research is still needed to control for heterogeneity among studies and to further explore the relationship between crop rotation and soil microorganisms.