Effects of Partial Organic Fertilizer Substitution on Soil Physicochemical Properties, Enzyme Activities, Microbial Communities, and Maize Yield: A Two-Year Field Study

Partial substitution of chemical fertilizer with organic fertilizer is an important strategy for optimizing fertilization and mitigating soil degradation caused by excessive chemical fertilizer application. However, systematic studies comparing the effects of different substitution ratios on soil properties, enzyme activities, and microbial communities remain scarce. A two-year field experiment was conducted with five treatments: no fertilization (Control), chemical fertilizer alone (CF), 20% organic fertilizer substitution (M20), 40% substitution (M40), and 60% substitution (M60). High-throughput sequencing was used to analyze soil bacterial and fungal communities. The M40 treatment significantly increased soil organic matter (17.96% and 30.18%, respectively), available nitrogen (6.85% and 20.30%, respectively), and available phosphorus (30.74% and 52.65%, respectively) compared with CF in both years, with more pronounced improvements observed in 2025. Furthermore, the M40 treatment also enhanced urease and sucrase activities in both years but reduced alkaline phosphatase (ALP) activity in 2025. Microbial community analysis revealed that the M40 treatment enriched beneficial microorganisms, including Proteobacteria, Acidobacteriota, Basidiomycota, Vicinamibacteraceae, Botryotrichum, and Tausonia, while inhibiting the pathogenic fungus Fusarium. Compared with CF, the M40 treatment increased maize yield by 7.04% and 8.10% in 2024 and 2025, respectively, which was the highest among all treatments. Mantel tests indicated that yield was positively correlated with available phosphorus, available potassium, total nitrogen, total phosphorus, and urease activity, but negatively correlated with ALP activity in 2025. Our findings demonstrate that 40% organic fertilizer substitution synergistically improves soil fertility, optimizes microbial community structure, and promotes crop yield, providing empirical evidence for optimizing fertilization regimes in maize production.