Diversified Crop Rotation Enhances Soil Health and Microbial Diversity in Successive Maize Cropping on Sodic Soils

Intensive monoculture exacerbates soil compaction and sodification in the West Liao River Plain. This study evaluated legacy effects of diversified 3-year rotations on sodic soil health (ESP > 15%, ECe < 4 dS m−1) during two subsequent maize seasons. Rotations incorporating salt-tolerant forages and deep-rooted crops (sugar beet–Echinochloa–sorghum and Echinochloa–tall fescue–silage corn) significantly reduced bulk density (8.6–13.1%) and exchangeable sodium percentage (up to 14.1 percentage points) relative to continuous monoculture. Treatments with maximum desalination (22.6% reduction) enhanced fungal α-diversity by 98.0%, while forage-dominated systems enriched Acidobacteriota by 35.2%, shifting bacterial communities toward oligotrophic dominance. Structural equation modeling confirmed that rotation effects on enzyme activity were mediated through reduced bulk density and ESP. These systems provide effective biological models for sustainable maize cultivation in sodic soils via synergistic physical-chemical-biological amelioration.