Chemical and microbial properties of various compost products

Abstract

Chemical and microbial characterizations were carried out for forty-four compost products, whose raw materials were classified into seven categories: wood, coffee ground, grass, buckwheat shells, animal manure, food waste, and others. Microbial community structure in the composts was examined by quinone profile analysis. Values of the chemical and microbial properties varied considerably as follows: moisture content 3.1–82.7%, pH 4.38–9.44, electric conductivity (EC) 0.12–17.08 mS cm⁻¹, total carbon (TC) content 16.9–51.0%, total nitrogen (TN) content 0.61–9.83%, C / N ratio 5.2–53.1, ash content 4.2–63.2%, total quinone (TQ) content 0.0–215.2 µmol kg⁻¹ dry sample, and value of quinone diversity (DQ) index 0.0–20.8. The wide range in the values expressed the diversity of the chemical and microbial properties of various compost products. The chemical properties were related to the raw materials while the microbial properties tended to be less related. Total menaquinone contents were higher than the total ubiquinone contents in most of the composts. The common major quinone species was menaquinone-7, indicating the predominance of Bacillus. The average mole fractions of menaquinones with partially saturated and long side-chains accounted for about 37% of the TQ content, indicating the proliferation of Actinobacteria. Multiple regression analysis suggested that microbial properties were significantly related to the moisture content, pH, and C / N ratio of the compost products. The DQ increased with the increase of the quinone contents and became stable at the value of about 16.5 in the composts with more than 50 nmol kg⁻¹ of quinones. At the same time these values were observed only in the composts with C / N ratios lower than 20.