CARBON AND NITROGEN TRANSFORMATION DURING COMPOSTING OF SWEET SORGHUMBAGASSE

Two types of compost, consisting of sweet sorghum bagasse with either sewage sludge or a mixture of pig slurry and poultry manure, were stud ied in a pilot plant using the Rutgers system. The total degradation o f the piles as determined by the weight loss of organic matter during the bio-oxidative and maturation phases accounted for 64% of the organ ic matter applied and followed a first-order kinetic function. Concent rations of total and organic N increased during the composting process as the degradation of organic C compounds reduced the compost weight. Losses of N through NH3 volatilization were low, particularly in the compost with sewage sludge due to pH values of <7.0 and the low temper atures reached in the compost during the first 2 weeks. The C:N ratio in the two composts decreased from 24.0 and 15.4 to values between 12 and 10. Increases in cation exchange capacity and in fulvic and humic acid-like C revealed that the organic matter had been humified during composting. The humification index, the C:N ratio, fulvic:humic acidli ke C, and cation exchange capacity proved to be the most suitable para meters for assessing the maturity of these composts.