CARBON MINERALIZATION FROM ORGANIC WASTES AT DIFFERENT COMPOSTING STAGES DURING THEIR INCUBATION WITH SOIL

The decomposition of seven different organic waste mixtures prepared w ith sewage sludges, animal manures, city refuse and industrial and pla nt residues, was studied during their aerobic incubation with soil. Th e waste mixtures were composted by the Rutgers static pile system, and four samples of each mixture were collected at various composting sta ges: the initial mixture, and samples taken during the thermophilic ph ase, at the end of the active phase and after maturation. These sample s were added to a calcareous silt loam soil at a rate of 200 mg per 10 g soil, and the CO2-C evolution was determined during 70 days of aero bic incubation at 28 degrees C. Carbon mineralization decreased as the composting time lengthened. The lowest values of C mineralization wer e found for the mature samples, and only a compost which had not attai ned an advanced degree of maturation gave results higher than 25% of T OC. Carbon mineralization followed a combined first- and zero-order ki netic model in most of the samples, suggesting that the organic C of t he composting wastes was made up of two organic pools of differing deg rees of stability. However, the differences in the slow C mineralizati on pool at the end of the active phase and after maturation were very small, indicating that the organic matter at both stages was of a simi lar microbial stability. Comparing the C mineralization which takes pl ace in soil and during composting, it can be concluded that composting is the best way of obtaining maximum C stabilization, which is an imp ortant factor in soil conservation and reclamation. (C) 1998 Elsevier Science B.V. All rights reserved.