Aerobic composting of chips from clear-cut trees with various co-materials

Swollen chips made from trees felled during clear-cutting were composted with various organic and inorganic materials in an aerobic composting reactor for 5 months and then piled for 5 months. The organic materials included chicken feces, urea, nitrogenous lime (calcium cyanamide, manure), and material rapidly composted from food garbage in 24-h bacterial fermentation, while the inorganic materials were coal ash and volcanic ash. In this paper, we first attempt to estimate the quality and degree of maturity of each compost from its chemical properties. Furthermore, we try to calculate the maturity of the fermented wood chip composts from their mixture ratio of the initial materials by multiple linear regression analysis. We measured changes in the C/N ratio, nitrate nitrogen (NO3-N) content, percentage of humic acid in the alkali soluble fraction (PQ), cation exchange capacity, pH, and EC during the composting period. The degrees of maturity of the composts were estimated via a plant growth test using Chinese cabbage. We found that the CN ratio, NO3-N concentration, and PQ were suitable for estimating the degree of maturity of wood chip composts. For maturity, the CN ratio should be less than 14, the PQ more than 66.2, and the NO3-N concentration more than 853 mg kg−1. We devised an equation to estimate the degree of maturity after 10 months by a multiple linear regression analysis from the mixing ratio of wood chips and the co-composted materials. From the multiple linear regression analysis, the above three indices of compost maturity could be estimated from the mixing ratio of the initial materials. This equation should enable us to determine the degree of compost maturity after 10 months based on the initial mixing ratio.