Co-Composting Process: A Study for Reducing C/N Ratio and Assessment Quality of Compost Product via Measurement of Phytotoxicity by Different Feedstock Mixtures

Abstract

Co-composting is a method for utilized organic waste for agriculture sectors. C/N ratio and feedstock mixtures are mainly for successful on composting process. Coffee husk has high C/N ratio 105.21. Insufficient C/N ratio would be adjusted by accumulation extra material such as animal manure and organic waste for easy nutrient from organic waste absorb into the soil and plant. The present study was conducted in laboratory with aimed to reducing C/N ratio by aerobic co-composting process and enhancing quality of coffee husk, also assessment the quality of co-compost via measurement of phytotoxicity by germination index. Two piles were conducted by mixing coffee husk, chicken manure, and cow dung (Pile. 1) and coffee husk, chicken manure, cow dung, and rice grain (Pile. 2). Samples were collected in 0, 7, 14, 21, 70, and 84 days for analyzed C/N ratio, while in every 7 days for measured pH and EC (electrical conductivity). In addition, initial and in the end of cocomposting product was analyzed; NH4 + , NO3-, total nitrogen, total phosphorus, total cations (K, Ca, Mg), while for germination index was analyzed after co-composting process. The results showed that (Pile. 2) the greatest reduction in C/N ratio with 14.32 ± 0.2 and highest germination index (GI) for Komatsuna (Brassica rapa var. Perviridis) with 131.5%. Thus, this indicated higher value of total nitrogen which caused by added rice grain to the co-composting pile.