Changes in Carbon Fractions during Composting of Plant Wastes and the Influence of a Humic Extract on Soil Microorganism Growth

A composting experiment was carried out to assess the best parameters as indicators for degree of compost maturity and to determine humification indices for practical use. The effect of humic acids extracted on soil microorganisms growth was also simultaneously investigated in vitro under axenic conditions. The parameters used were oxidizable carbon (Co), alkaline-extractable carbon (Cex), humic and fulvic-like carbon (Cha, Cfa), humification ratio (HR), humification index (HI), percent humic acid (Pha) and Cha/Cfa ratio. Results indicated that HR, HI, Pha and Cha/Cfa ratio could be used to describe the evolution of organic matter during the composting of horticultural residues as well as the humification degree of compost. Our microorganism incubation study showed that the addition of humates from lignocellulosic waste based compost at 1, 5 and 10% to the culturing medium enhanced bacterial growth while the above effect was not clearly observed when this product was added to fungi and actinomycetes. _____________________________________________________________________________________________________________