Assessing microbial population dynamics, enzyme activities and phosphorus availability indices during phospho-compost production

Purpose This study assessed changes in bio-quality indices and plant available P released during aerobic-thermophilic co-composting of different mix ratios of non-reactive ground phosphate rock (GPR) with poultry and cattle manures. Methods Aerobic-thermophilic co-composting of different mix ratios (5:5, 8:2, 7:3 and 9:1) of non-reactive GPR with poultry and cattle manures was carried out. Compost piles without GPR addition were included as control. Compost samples were taken at mesophilic, thermophilic, cooling-stabilization and maturing phases for microbial counts, enzyme activities and P assessment. Results Abundance of different microbial groups across the composting phases varied greatly (p < 0.001) mostly dominated by fungi that was generally more in the cattle than poultry manure-based phospho-composts. Fungi and actinomycetes counts in the composts were positively correlated with alkaline phosphatase and beta-glucosidase. A strong inter-correlation between beta-glucosidase and alkaline phosphatase (r = 1.000, p < 0.001) was observed, suggesting that both enzymes possess same origin. Alkaline phosphatase and beta-glucosidase contents in the phospho-composts showed negative correlation with water soluble P (r = - 0.65, p < 0.001), and Bray P1 and Fe-P contents (r = - 0 .15, p > 0.05) indicating inhibition of the P forms. Quantitatively higher P was obtained from poultry manure-based phospho-compost and in the 8:2 mix ratio at compost maturity. Microbial diversity and enzyme activity exerted positive impact on P mineralization and availability from the non-reactive GPR signifying the beneficial effect of co-composting. Conclusions Co-composting of P-rich non-reactive GPR with organic wastes containing variable chemical composition promotes microbial diversity during composting and increases plant available P content and compost fertilizer value.