Physicochemical and Biological Changes of Compost Inoculated with Pseudomonas Aeruginosa AAC1 and Rock Phosphate: Implications for P Availability

Abstract

Phosphorus (P) is an essential nutrient for plant growth, but its availability in soil is often limited. Present study was conducted to design compost enriched with phosphate-solubilizing bacteria (PSB) and rock phosphate (RP). Four compost piles were prepared with RP and 30:1 carbon-to-nitrogen (C: N). Out of these, two piles were inoculated with PSB strain Pseudomonas aeruginosa AAC1 (RP + AAC1) while two piles were left un-inoculated and served as control (RP). The physicochemical assessment of the designed compost revealed that the addition of RP and inoculation of P. aeruginosa AAC1 (RP + AAC1) significantly (p < 0.05) increased the composting temperature (over 58 °C), calcium (36.84%), magnesium (35%) and available P contents (43.50%) indicating the solubilization of inorganic P, Ca and Mg bound phosphates However, the addition did not significantly (p > 0.05) influence the carbon (C), carbon to nitrogen (C/N) ratio, organic matter, and ash content but significantly (p < 0.05) reduced the moisture content (41%) and pH (up to 5.4). After 60 days, all compost piles reached maturity at temperature ranges of 27-30 °C, pH level between 7.2–7.6, and moisture content 31-35%. Scanning electron microscopy and energy-dispersive X-ray spectrometry (SEM-EDS) confirmed the presence of elements including carbon (C), oxygen (O), magnesium (Mg), aluminum (Al), silicon (Si), calcium (Ca), and P (P) in the compost. Microbiological monitoring revealed the survival of P. aeruginosa AAC1 during the composting process even at higher temperatures (∼58 °C). Indigenous bacterial populations were recovered within the range of 109 - 1014 CFUg−1. Compost was also safe in regard to heavy metal concentrations. Thus, the results suggest that combining P. aeruginosa AAC1 and RP in compost can enhance the availability of soluble P, thus serving as an effective phosphatic biofertilizer.