Soil Management Modulates Maize Responses to Phosphate-Solubilizing Bacteria

Phosphorus (P) limitation constrains crop production in highly weathered tropical soils, and microbial inoculants may enhance P acquisition, although their effectiveness varies with edaphic conditions. We hypothesized that the effects of a phosphate-solubilizing bacterial inoculant on plant performance and belowground processes would depend on soil P status and no-tillage history. A two-year field experiment on an Oxisol in the Brazilian Cerrado (Chapadão do Sul, MS, Brazil) compared newly established, low-P (NTS-NC) and consolidated, high-P (NTS-C) no-tillage systems. Treatments combined 0, 50, or 100% of recommended P fertilization with or without BiomaPhos®, composed of Priestia megaterium CNPMS B119 and Bacillus subtilis CNPMS B2084. Grain yield, resin-extractable soil phosphorus (P-resin), root architecture, bacterial and arbuscular mycorrhizal fungal (AMF) communities, AMF colonization, and phosphatase activities were evaluated. Grain yield in NTS-C exceeded NTS-NC by 15.7% and 18.8% in 2021/2022 and 2022/2023, respectively. Inoculation × P interactions for yield and P-resin occurred only in NTS-NC in the second season. Inoculation altered root architecture, whereas P availability reorganized bacterial association networks. AMF responses were limited and season-specific, while inoculation reduced AMF colonization and phosphatase activity primarily in NTS-C. These findings confirm that inoculant performance is context-dependent and should be integrated with site-specific P fertilization strategies.