Dose-Dependent Growth Promotion and Rhizosphere Microbial Community Responses of Silage Maize to Bacillus amyloliquefaciens Biofertilizer
To verify the growth-promoting effects of Bacillus amyloliquefaciens on silage maize (Zea mays L.), optimize its application dosage, and elucidate rhizosphere microecological responses, this study executed field experiments in both conventional and saline-alkali soils. We comprehensively assessed how varying biofertilizer dosages (0, 300, and 600 kg ha−1) influenced crop phenotypes, soil physical and chemical attributes, and rhizosphere microbial communities. Results demonstrated that applying B. amyloliquefaciens substantially enhanced biomass and crude protein accumulation in silage maize, without compromising its ideal carbohydrate profile and fermentation characteristics. The observed growth stimulation was likely linked to efficient mobilization of native soil nutrients. Following biofertilizer application, significant surges in available potassium, available phosphorus, and inorganic nitrogen were recorded at both locations, coupled with successful pH buffering in the saline-alkali plots. Microbial analysis indicated a notable expansion of the copiotrophic Proteobacteria phylum, with the bio-inoculant displaying dose-dependent shifts. Specifically, Xanthobacteraceae was heavily recruited in standard agricultural soils to hasten nutrient mineralization, while stress-tolerant bacterial groups like Nitrosomonadaceae were stimulated under saline-alkali conditions. Furthermore, comprehensive phenotypic and nutritional evaluations demonstrated that, among the tested doses, an application rate of 300 kg ha−1 effectively optimizes crop performance. Higher doses do not yield proportional biological benefits, likely due to the carrying capacity limits of the rhizosphere microecology. In summary, B. amyloliquefaciens can support high-yield and high-quality silage maize production by activating soil nutrients and remodeling the core rhizosphere microbiome in a habitat-specific manner. Among the tested doses, 300 kg ha−1 showed the best performance, but further studies with lower doses and longer durations are needed to determine the true optimal application rate and to assess its economic and environmental sustainability.