Effect of Microbial Ratio, Storage Temperature, and Packaging on the Viability and Stability of Co-Inoculated Rhizobium tropici and Azospirillum spp. in Nitrogen-Fixing Biofertilizer
DOI:
https://doi.org/10.65141/tjeraff.v5i2.273Keywords:
biofertilizer stability, Rhizobium tropici, Azospirillum spp, co-inoculation, microbial viabilityAbstract
The privatization of Bio-N biofertilizer in the Philippines created an urgent need for locally produced and cost-effective alternatives. In response, the Department of Agriculture–Ilagan Soil Laboratory (DA-ISL) developed a dual-strain biofertilizer by co-formulating Rhizobium tropici, isolated from wild tallgrass (Saccharum spontaneum), with Azospirillum spp., a well-established nitrogen-fixing bacterium. This study aimed to assess the long-term viability and stability of co-inoculated formulations under varying microbial ratios, packaging types, and storage conditions.
An experimental research design was employed, testing five mixtures of R. tropici and Azospirillum spp. stored for 12 months under ambient (28–32 °C) and air-conditioned (20–25 °C) conditions. Viability was assessed monthly using serial dilution and spread plate techniques, with colony-forming units (CFU/g) analyzed to determine formulation and storage performance.
Results showed that microbial populations typically stabilized or increased in the first two to three months before gradually declining. Among all treatments, Mixture A (50% R. tropici + 50% Azospirillum spp.) packaged in aluminum foil and stored under air-conditioned conditions demonstrated the highest stability, maintaining 2.6 × 10? CFU/g at Month 12. In contrast, R. tropici–dominant mixtures exhibited sharper viability losses, while Azospirillum alone remained more resilient. Packaging and storage temperature emerged as critical factors influencing shelf life.
These findings highlight the potential of co-inoculated biofertilizer as farmer-ready product. Balanced microbial ratios, protective foil packaging, and cool storage can ensure product reliability, reduce dependence on commercial inoculants, and strengthen farmer adoption of sustainable soil fertility practices. Future research should validate field performance, assess cost-effectiveness, and explore alternative carriers to support large-scale adoption and farmer use.
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