<p>Phosphorus (P) is crucial for plant growth, but its bioavailability in soil is often limited. Integrating phosphorus-solubilizing bacteria (PSB) with P-fertilizers can enhance P solubilization in the soil and uptake by crops. However, the effectiveness of this combination depends on several factors, including the specific bacterial strains and the types of fertilizers used. An often-overlooked factor is the number of microbial cells used for inoculation, which can significantly affect the outcomes. This study evaluated the effects of two PSB strains, <i>Arthrobacter nicotinovorans</i> EAPAA (B1) and <i>Rhodococcus</i> sp. EC35 (B2), inoculated at two sizes, S1 (3 × 10³ cells g⁻¹ soil) and S2 (3 × 10⁶&#xa0;cells g⁻¹ soil), on biomass, shoot nutrient concentration of maize grown in P-fertilized soil. Selected soil properties, such as soil available P and enzymatic activity, were also assessed. Results indicated that lower inoculum sizes (S1) were linked with higher maize biomass and increased soil phosphatase and urease activities, suggesting that a lower bacterial cell density may better trigger growth-promoting traits and reduce antagonistic interactions with native soil microbiota. However, bacterial treatments didn´t increase soil bioavailable P or its concentration in plant tissues, regardless of the inoculum size. This suggests that the benefits provided by the PSB were primarily related to their growth-promoting traits, which were pronounced at a lower inoculation rate. These findings highlight the importance of optimizing inoculum size for effective biofertilizer strategies and underscore the need for further research into microbial dynamics and long-term impacts across diverse agronomic systems.</p>