Formulation and Effects of P Biofertilizer in Okra

Phosphorus is essential for crop growth, yet its availability is limited in many tropical soils due to fixation by calcium, iron, and aluminium compounds. This constraint affects the productivity of okra (Abelmoschus esculentus), a key vegetable crop in Nigeria. To explore sustainable alternatives to chemical fertilisers, this study assessed the effects of two phosphate-solubilizing fungi (PSF),Aspergillus niger and Penicillium chrysogenum formulated with various organic carriers and inoculum loads on soil nutrient availability and okra growth. The experiment followed a Completely Randomized Design with three factors: fungal strain (2 levels), carrier material (4 levels), and inoculum load (10⁶ and 10⁸ spores/mL), resulting in 16 treatment combinations, each replicated thrice. Carriers included poultry manure, cow dung compost, their mixtures, and a control. Parameters measured included soil microbial population, nutrient content (N, P, K), pH, plant tissue nutrient concentration, and plant height. Data were analysed using independent t-tests (p < 0.001). Results showed that PSF inoculation significantly improved soil microbial activity, phosphorus solubility, and plant growth. The highest microbial count (7.91 log CFU/g) and soluble phosphorus (12.28 mg/kg) were recorded in P. chrysogenum-inoculated poultry manure at 10⁸ spores/mL. The tallest plants (59.85 cm) and highest nitrogen (72.59 mg/kg) occurred with A. niger and cow dung. PSF applications enhanced phosphorus availability up to 27.24 mg/kg, nearly doubling that of the control. The study confirms the potential of PSF-based biofertilisers as eco-friendly tools for improving phosphorus availability and okra yield in Nigerian soils.