Effectiveness of compost inoculated with phosphate solubilizing bacteria

The present study was carried out to design a phosphate solubilizing bacterial (PSB)-based biofertilizer using locally produced fruit waste.

Two PSB strains Pseudomonas aeruginosa CMG4 and AAC1 were inoculated into compost. Six compost piles were prepared with carbon:nitrogen (C:N) ratio 30:1. Four piles were inoculated with PSB and two piles served as a control. After 125 days, composts were considered mature at 29-31°C in the pH range of 7.1-7.3 and 32%-35% moisture content (MC). Accessible calcium (Ca) content increased up to 50 g kg^-1 . Microbial analysis showed the survival of P. aeruginosa species in the maturing compost even at higher temperature (~53°C). Native bacterial load was retrieved in the range of 10⁹ -10¹¹  CFUg^-1 . Heavy metal concentrations including copper (Cu), lead (Pb), chromium (Cr) and cadmium (Cd) were found to occur below critical thresholds. Seed germination index for compost toxicity was found to be >80%, significantly higher than animal manure and chemical fertilizer, that is, 78% and 31%, respectively, suggesting non-toxicity.

The evaluation of prepared compost by physicochemical parameters revealed that inoculation of P. aeruginosa does not affect the temperature, MC, carbon to nitrogen ratio, organic matter and Mg content but significantly increased the accessible Ca content, suggesting the solubilization of inorganic Ca bound phosphate. Compost was safe in terms of heavy metal concentration and seed germination.

This study encourages that the PSB-rich tailored compost can be utilized as a phosphatic biofertilizer to fulfil the demand for phosphorus which would improve and sustain soil fertility.