Synergistic Effects of Leguminous Cover Crops and Bacillus cereus Inoculation on Soil Microenvironment and Bacterial Communities in Coffee Agroecosystems of the Dry–Hot Valley

Background: Intensive agriculture in fragile, dry–hot valleys degrades coffee plantation soils. Combining leguminous cover crops with microbial inoculants is promising, yet their synergy remains unresolved. Methods: In a field trial, we established Medicago sativa L. (ZB1) and Vicia villosa Roth var. glabrescens (ZB2) cover crops following Bacillus cereus inoculation, then assessed soil chemistry, nitrate–nitrogen (NO3−-N), key enzyme activities (catalase, CAT; sucrase, IA; urease, UA), and bacterial communities; redundancy analysis linked edaphic variables to community structure. Results: Co-application remodeled the soil microenvironment. ZB1 moderated pH from 7.92 (weakly alkaline) to 7.46 (near neutral) and increased total nitrogen (TN) and potassium (K). NO3−-N rose 1.38-fold (ZB1) and 2.14-fold (ZB2), indicating improved N retention and reduced leaching risk. CAT, IA, and UA activities increased concurrently. The bacterial community shifted from Acidobacteria toward Bacteroidetes and was enriched in taxa including Flavobacterium. Redundancy analysis identified total nitrogen as the primary environmental driver of community change. Conclusions: Leguminous cover crops combined with B. cereus synergistically improved soil conditions and reorganized bacterial communities in dry–hot valley coffee systems, providing field-scale evidence and practical guidance for sustainable agroecosystem management.