The expansion of animal husbandry for food production has necessitated effective management of livestock waste, including cattle manure and poultry litter. Using these byproducts as organic fertilizers in agriculture represents a sustainable approach to their disposal. While these residues offer known benefits for soil health and crop productivity, further studies are needed to explore the effect of different manure microbiota on soil composition. The objective of this study was to address this gap and contribute to the advancement of this area. A randomized block design experiment was set up in the field with three replications per treatment, including the application of cattle manure, poultry litter, and a control treatment without fertilizer. After a 60 day period, the chemical characteristics and bacterial population composition of the soil were analyzed using 16S rRNA gene sequencing. Organic carbon, phosphorus (P), aluminum (Al), and the pH level played pivotal roles in changing the structure of the soil’s bacterial community. Notably, the incorporation of poultry litter induced more pronounced changes in both the chemical properties and bacterial community composition compared with cattle manure. Bacterial groups were enriched in the soils treated with poultry litter, which may indicate enhanced soil fertility. This association may stem from both the chemical alterations resulting from poultry litter application and the direct transfer of microorganisms from this organic fertilizer to the soil.

Plant growth-promoting bacteria (PGPBs) offer a sustainable alternative for enhancing crop productivity in low-fertility tropical soils. In this study, 30 bacterial isolates were screened in vitro for multiple PGP traits, including phosphate solubilization (from aluminum phosphate—AlPO₄ and thermophosphate), potassium release from phonolite rock, siderophore production, indole-3-acetic acid (IAA) synthesis, ACC deaminase activity, and antagonism against Fusarium spp. Statistical analysis revealed significant differences (p < 0.05) among the isolates. The most efficient isolates demonstrated a solubilization capacity ranging from 24.0 to 45.2 mg L⁻¹ for thermophosphate and 21.7 to 23.5 mg L⁻¹ for potassium from phonolite. Among them, Pseudomonas azotoformans K22 showed the highest AlPO₄ solubilization (16.6 mg L⁻¹). IAA production among the isolates varied widely, from 1.34 to 9.65 µg mL⁻¹. Furthermore, 17 isolates produced carboxylate-type siderophores, and only Pseudomonas aeruginosa SS183 exhibited ACC deaminase activity, coupled with strong antifungal activity (91% inhibition). A composite performance index identified P. azotoformans K22, E. hormaechei SS150, S. sciuri SS120, and B. cereus SS18 and SS17 as the most promising isolates. This study provides a valuable foundation for characterizing plant growth-promoting traits and identifies key candidates for future validation and the development of microbial consortia.