Silage maize is vital to livestock development in northern China, but intensive chemical fertilization has led to soil degradation and reduced productivity. Bio-organic fertilizers offer a sustainable alternative, though their effects on soil multifunctionality remain underexplored. This study evaluated the impact of combining decomposed cow manure, Bacillus amyloliquefaciens, and mineral potassium fulvic acid with chemical fertilizers (NPK) on silage maize yield, soil microbial diversity, and ecosystem multifunctionality (EMF). Field experiments showed that bio-organic fertilization increased silage maize yield by 10.23% compared to chemical fertilizers alone, primarily by boosting labile organic carbon and soil enzyme activity. It also enhanced bacterial richness and diversity, with little effect on fungal communities. Microbial network analysis revealed more complex and stable bacterial networks under bio-organic treatments, indicating strengthened microbial interactions. Random forest and structural equation modeling (SEM) identified soil carbon storage and bacterial diversity as key drivers of EMF, which integrates soil functions such as nutrient cycling, decomposition, enzyme activity, and microbial diversity. These findings suggest that soil bacterial diversity and its interactions with soil properties are critical to both crop productivity and soil health. The optimal fertilization strategy for silage maize in this region involves the combined use of cattle manure, Bacillus amyloliquefaciens, mineral potassium fulvic acid, and NPK fertilizers. This approach improves yield, microbial diversity, and soil multifunctionality. Future studies should consider environmental variables and crop varieties across diverse regions to support broader application.

Soil microbial communities are fundamental to soil health and ecosystem functioning in agricultural landscapes. This study assessed how soil nutrient variation influences microbial community structure and ecosystem multifunctionality in tea gardens across three counties in Longnan, China. Key findings revealed that Kangxian tea garden soils exhibited 18–25% higher bacterial and fungal richness and diversity indices than Wenxian, which had the lowest values among the three counties. Co-occurrence network analysis indicated a 32% higher proportion of positive (cooperative) interactions among microbial taxa in Wenxian soils. Null model analysis showed that bacterial community assembly was primarily driven by deterministic heterogeneous selection, whereas fungal assembly was governed by stochastic ecological drift. Functionally, Wenxian soils demonstrated 22% higher carbon sequestration, 19% higher nutrient storage, and 17% higher nutrient supply than the other counties (p < 0.05), while Kangxian soils had 21% greater nutrient cycling and overall ecosystem multifunctionality. Soil C/P and N/P ratios significantly influenced carbon sequestration, nutrient storage, and multifunctionality (explaining up to 48% of the variance), while soil pH was a key driver of carbon sequestration, nutrient supply, and cycling. Both bacterial and fungal community structures significantly impacted nutrient storage and multifunctionality. Regional differences in soil nutrients, shaped by tea garden management, directly influence microbial community traits and ecosystem multifunctionality. Targeted nutrient management and enhanced microbial diversity are key to improving soil multifunctionality and sustainability in tea agroecosystems.