MICROBIAL INDICATORS FOR SAWDUST AND BARK COMPOST STABILITY AND HUMIFICATION PROCESSES

To what extent some microbial index ratios are suitable for use as ear ly criteria for the level of compost stability during aerobic composti ng of coniferous sawdust and bark at mesophillic conditions was studie d. Evolution of the specific respiration activity (CO2-C/biomass C) an d the ratios between some groups of microorganisms were followed as a function of composting time. The specific respiration activity was fou nd to be an early and most reliable indicator of compost stability. Th e peroxidase and polyphenoloxidase enzyme activity during composting, as well as the composition of newly-formed humus substances were studi ed The duration of composting increased the quality of newly-formed hu mus substances (C-h.a.:C-f.a. ratio; Ca-complexed humic acid and resis tance of organo-mineral complexes). The quality of humus substances co uld be used to assess compost stability. However, the results can be a pplied only under defined conditions.