Assessment of Microbial Population Dynamics, Enzyme Activities and Phosphorus Availability Indices during Phosho-Compost Production.

Changes in population size of different microbial groups (actinomycete, bacteria and fungi), 3 different enzymes (alkaline phosphatase, dehydrogenase and β-glucosidase) and phosphorus (P) release characteristics were studied during the co-composting process of non-reactive ground phosphate rock (GPR) with poultry and cattle manures. Four phospho-compost piles were prepared by mixing different ratios (5:5, 7:3, 8:2, 9:1) of the manures with GPR on dry mass basis. Compost pile without GPR addition for the two manures was included as control. During co-composting, representative samples were taken at early and late mesophilic, thermophilic and maturity stages for microbial, enzyme activity and P analyses. Results showed a significantly varied abundance of the different microbial groups across the four composting stages largely dominated by fungi. Microbial abundance and enzyme activity were generally more in cattle than poultry manure-based phospho-composts. The complete absence of bacteria at the advanced mesophilic and thermophilic stages particularly in 8:2 poultry manure-based phospho-compost suggests that they might have been killed during the co-composting process. Fungi and actinomycetes counts in the different phospho-composts were positively correlated with alkaline phosphatase and β-glucosidase. Alkaline phosphatase and β-glucosidase had same correlation value with fungi and actinomycete counts. There was a strong inter-correlation between β-glucosidase and alkaline phosphatase (r = 1.000, p < 0.001) suggesting that the enzymes may be from the same origin. Significantly high positive correlation between dehydrogenase and Bray P1 and inorganic P were obtained. Both alkaline phosphatase and β-glucosidase showed negative correlation with Bray P1 and inorganic P contents suggesting inhibition of both P forms in the different phospho-composts. Quantitatively higher P was obtained in 8:2 mix ratio at compost maturity. Findings from this study revealed the potential impact of both microbial diversity and activity on P mineralization and availability from non-reactive ground phosphate rock.

Key words: Phospho-compost, Compost quality, Microbial diversity, Enzyme activities, Nutrient cycling, Phosphate rock