The Impact of Various Additives on the Composting Process of Organic Compounds on the Biological Properties and Humification of Compost

This study investigated the effect of biochar, leonardite, and coal on some maturing indices, humification, microbial respiration, and enzymatic activity in a co-compost of manure and forest organic materials. The experiment was conducted in a factorial design with three replications at the compost production site for three months. The first factor included biochar treatment (2 and 4 percent), leonardite (2 and 4 percent), and coal (2 and 4 percent by weight) mixed with the raw materials, and the second factor was time spanning from the first week to week 12. During the composting process, weekly sampling of the compost pile was performed, and some biological and humification indices in the compost were measured. The results showed that the leonardite (2%, w/w) treatment had the highest temperature (61.2 degrees Celsius), the longest duration of the thermophilic phase (18 days), and the highest nitrogen content (2.1%). The coal (4%, w/w) treatment led to a significant increase in electrical conductivity, and the biochar (2%, w/w) treatment increased organic carbon (25.75%) and C/N ratio (15.8%) in the final compost. Adding leonardite increased the humic and fulvic acid percentage and created the highest humification indices. The additives used in this study did not significantly affect the seed germination index. Biochar (2, 4%, w/w) treatments significantly increased urease and phosphatase enzyme activities, but no significant difference was observed in dehydrogenase enzyme activity compared to the control. This study's results demonstrate that biochar and leonardite are more effective than coal in improving enzymatic activities and humification indices in the composting process.