Effects of agricultural and forestry wastes on organic matter conversion and enzyme activity in livestock manure composting

Composting livestock and poultry manure through aerobic composting technology using agricultural and forestry wastes is an effective way to reduce environmental pollution and avoid waste of resources. Fresh cow manure supplemented with agricultural and forestry wastes was used for composting in pilot experiments. The effects of different agricultural and forestry wastes on the composting process were investigated by characterizing the differences in physical and chemical properties, the evolution of the material structure of organic matter and humus, and the changes in enzyme activities during the composting process. The results showed that in the early stage of composting, the easily degradable organic matter was degraded by microorganisms, resulting in an increase in the temperature of the compost. In addition, the contents of ammonium nitrogen (${\mathrm{NH}}_4^+ $-N), humic acid (HS) and fulvic acid (FA) decreased gradually. As the high-temperature period continued, microorganisms began to accelerate the degradation of difficult-to-degrade macromolecular organic matter, leading to a decrease in cellulose and hemicellulose contents and a rapid increase in the proportion of lignin content. When the temperature dropped, the activity of nitrifying bacteria was gradually increased, and a large amount of ammonium nitrogen was converted into nitrate nitrogen (${\mathrm{NO}}_3^- $-N). Furthermore, the reduction of organic matter content in the pile body diminished the urease activity. In the later stage of composting, the proportion of refractory lignin was higher, the utilization of organic matter was slow, and the activities of polyphenol oxidase and catalase were inhibited. The research results can provide a scientific basis for optimizing the composting process and improving the quality of composting.