Leguminous Green Manure Intercropping Promotes Soil Health in a Citrus (Citrus reticulata) Orchard

The intercropping of green manure is an important and sustainable production method in citrus orchards (Citrus reticulata). However, few studies focus on the impact of annual and perennial green manure on soil health, particularly soil microbiome and properties in acid soil. Our research objective was to explore the potential effects on soil health by intercropping with annual and perennial leguminous green manures in acid soil citrus orchards of southwestern China. The leguminous green manures used were alfalfa (Medicago sativa) and hairy vetch (Vicia villosa). The results showed that intercropping with green manure increased the total nitrogen, nitrate nitrogen, and available phosphorous in the soil by 48.67~74.67%, 50.00~96.67%, and 44.48~45.04%, respectively. Intercropping with alfalfa significantly increased the activity of soil sucrase 63.75%, and intercropping with hairy vetch increased the activity of β-1,4-glucosidase 44.38% in the soil compared to the monoculture treatment. Intercropping hairy vetch and alfalfa altered the diversity and composition of the soil microbial community and enriched the soil with beneficial fungi and bacteria, including Mortierella and Streptomyces. The richness increased by 58.72% and 17.90% in alfalfa intercropping treatment. In conclusion, intercropping leguminous green manure improved the nutrients and activity of the enzymes in the soil and enriched the antagonistic microbiome in the soil, promoting soil health in the citrus orchard.