Planting Diversification Enhances Phosphorus Availability and Reshapes Fungal Community Structure in the Maize Rhizosphere

Intercropping with green manures is an effective practice for increasing agricultural production and reducing environmental issues. However, the effects of green manure type and intercropping patten on soil nutrient availability and microbial communities remains underexplored. In the present study, the impacts of three green manure–maize intercropping patterns on maize yield, rhizosphere nutrient availability, and soil fungal community were evaluated. Four treatments (three replicate plots for each) were involved, including a monoculture treatment (MC) as a control and three intercropping patterns as follows: maize–ryegrass (Lolium perenne L.) (IntL), maize–forage soybean (Fen Dou mulv 2, a hybrid soybean cultivar) (IntF), and maize–ryegrass–forage soybean (IntLF) intercropping. The results showed that all three intercropping patterns significantly increased maize yield and rhizosphere available phosphorus (AP) compared with MC. Intercropping shifted the dominant assembly process of the maize rhizosphere fungal community from stochastic to deterministic processes, shaping a community rich in arbuscular mycorrhizal fungi (AMF) and limited in plant pathogens, primarily Exserohilum turcicum. AP showed significant correlations with fungal community and AMF, while maize yield was negatively correlated with plant pathogens. In addition, the dual-species green manure intercropping pattern (IntLF) had the strongest positive effects on maize yield, AP content, and fungal community compared with single-species patterns (IntL and IntF). These results illustrate the advantages of planting diversification in boosting crop production by improving nutrient availability and soil health in the rhizosphere and suggest that the maize–ryegrass–forage soybean intercropping system is a potential strategy for improving soil fertility and health.