Development and Greenhouse Evaluation of PGPR-Based Biofertilizers Using Agro-Waste Carrier Materials

Abstract

Aims: This study aimed to develop eco-friendly biofertilizers derived from agro-waste materials and formulated with Plant Growth-Promoting Rhizobacteria (PGPR) as sustainable alternatives to chemical fertilizers. Study Design: Experimental laboratory and greenhouse study. Place and Duration of Study: The study was conducted in the Department of Microbiology, Federal University Oye Ekiti, Nigeria, between January and April 2025. Methodology: Five rhizobacterial isolates- Bacillus thuringiensis (a), Lysinibacillus sphaericus, Pseudomonas fluorescens, Bacillus thuringiensis (b), and Alcaligenes sp., were characterized using morphological, biochemical, and molecular methods. The isolates were screened for plant growth-promoting traits, including indole-3-acetic acid (IAA) production, phosphate solubilization, siderophore production, ammonia production, and hydrolytic enzyme activities. Carrier-based formulations were prepared using sterilized sawdust (Khaya sp.) and rice bran (Oryza sativa). Microbial viability was monitored for eight weeks. Greenhouse trials using okra (Abelmoschus esculentus) evaluated plant growth compared with NPK fertilizer and an untreated control. Results: All isolates exhibited multiple growth-promoting traits, while L. sphaericus uniquely showed protease activity. The formulations maintained high viability (1.29 × 10⁷–8.91 × 10⁷ CFU/g). Sawdust supported L. sphaericus and B. thuringiensis (b), whereas rice bran supported P. fluorescens and B. thuringiensis (a). Notably, L. sphaericus + sawdust and P. fluorescens + sawdust significantly enhanced plant height and biomass compared with NPK and control. Conclusion: Agro-waste-based PGPR biofertilizers improved crop performance and offer a cost-effective, sustainable alternative to chemical fertilizers, promoting waste valorization and environmentally friendly agriculture.