Phosphate Solubilization and Plant Growth-Promoting Potential of Penicillium oxalicum (Bt9) in Eppawala Rock Phosphate-Enriched Compost

The frequent application of chemical phosphate (P) fertilizers is costly and has emerged as a major concern in the agricultural sector of Sri Lanka. Therefore, the present study evaluated the impact of the fungal inoculum Penicillium oxalicum (Bt9) on the bio-solubilization of Eppawala Rock Phosphate (ERP)-enriched compost. A Completely Randomized Design (CRD) was employed, comprising four compost treatments, each replicated four times. Treatment 1 (T1) was amended with P. oxalicum (Bt9) and sugar; Treatment 2 (T2) was amended solely with P. oxalicum (Bt9); Treatment 3 (T3) was amended solely with sugar, and Treatment 4 (T4) served as the control, lacking both P. oxalicum (Bt9) and sugar. The released bioavailable phosphorus (P) content of each treatment was determined using the molybdenum blue method. A pot experiment was conducted using red cowpea (Vigna unguiculata), grown in a 1:1 mixture of phospho-compost and soil, to evaluate the effect of ERP bio-solubilization by P. oxalicum (Bt9) on plant growth. The results showed significantly higher (p ≤ 0.05) values for plant growth parameters, including shoot length, root length, and total plant length, in Treatments 1 and 2 compared with Treatments 3 and 4. The highest shoot length, root length, and total plant length were recorded in Treatment 1, with values of 26.58 ± 2.44 cm, 11.36 ± 1.48 cm, and 54.24 ± 2.64 cm, respectively. The study concluded that P. oxalicum (Bt9) significantly enhanced phosphate solubilization and promoted the growth of red cowpea (Vigna unguiculata). Therefore, ERP-enriched compost inoculated with P. oxalicum (Bt9) may be considered a sustainable alternative to imported chemical phosphate fertilizers.