Chemical and biological changes during composting of different organic wastes and assessment of compost maturity

Changes in organic C, total N, C:N ratio, activities of cellulase, xylanase and protease, and microbial population were determined during composting of different organic wastes such as mixture of sugarcane trash and cattle dung, press mud, poultry waste and water hyacinth biomass. There were losses of N in poultry waste and water hyacinth with the effect an initial increase in C:N ratio was observed which decreased later on due to decomposition. The activities of cellulase, xylanase and protease were maximum between 30 and 60 days of composting in various wastes. Similar trend was observed with respect to mesophilic bacterial and fungal population. Various quality parameters like C:N ratio, water soluble C (WSC), CO2 evolution and level of humic substances were compared after 90 day composting. There was statistically significant correlation between C:N ratio and CO2 evolution, WSC and humic substances. Significant correlation between CO2 evolved and level of humic substances was also observed. The study shows that no single parameter can be taken as an index of compost maturity. However, C:N ratio and CO2 evolved from finished compost can be taken as the most reliable indices of compost maturity.