Soil Microbial Community Driven by Soil Moisture and Nitrogen in Milk Vetch (Astragalus sinicus L.)-Rapeseed (Brassica napus L.) Intercropping

The soil microbial community is not only driven by plant composition but is also disturbed by the soil environment. Intercropping affects the soil microenvironment through plant interaction, but the understanding of the relationship between soil microbial community and environment in intercropping is still weak. In this study, milk vetch intercropping with rapeseed was used to explore the interaction between soil microorganisms and environment. The results showed that the soil moisture content of intercropping was higher than that of monoculture during the reproductive period of rapeseed growth (flowering and podding stages). The contents of soil total nitrogen and alkali-hydrolyzable nitrogen in intercropping were higher than those in monoculture. The dominant soil microbial communities in intercropping were the same as in monoculture and included Chloroflexi, Proteobacteria, Actinobacteria, Acidobacteria, Firmicutes, Gemmatimonates and Bacteroidetes. However, intercropping increased the Shannon index and decreased the Simpson's index of the soil microbial community. The changes in the soil microbial community were mainly related to soil temperature, moisture, pH, total nitrogen, alkali-hydrolyzable nitrogen and available potassium. Moreover, there was a negative correlation between soil moisture and microorganisms and a positive correlation between nitrogen and microorganisms. Thus, milk vetch-rapeseed intercropping could not only improve soil nitrogen content, but also change soil microbial community diversity. In dryland red soil, the effect of milk vetch-rapeseed intercropping on soil moisture and nitrogen was the key factor contributing to the changes in the soil microbial community. When planting rapeseed in the future, we could consider the application of intercropping with milk vetch, which can contribute to regulating the soil nitrogen pool and improving microbial diversity.