Comparison of four low-technology composting methods for market crop wastes

Four methods for composting, pit-cover (PC), pit-open (PO), above ground-open (AO) and above ground-covered (AC), were compared for their effect in accelerating compost maturity using market crop waste (MCW). The composting process was monitored through determining changes in temperature and pH, with compost maturity indices measured in terms of variations in water-soluble carbon (WSC), ammonium-N (NH4+–N) and nitrate-N (NO3-–N), and C/N, NH4+–N/NO3-–N, WSC/organic N and WSC/total N (TN). Total organic carbon (TOC), nitrogen (TN), potassium (TK) and phosphorus (TP) were also determined. Temperature rapidly increased from mesophilic to thermophilic and gradually reduced through maturation phases. A similar pattern was recorded for pH, which reached a slightly alkaline level at maturity. Composting significantly (p < 0.05) decreased the concentrations of TOC, TN, TP, TK, NH4+–N and WSC and increased that of NO3-–N. All four low-technology composting methods used in this study produced mature composts within 63 days. Suitable maturity indicators for MCW compost were C/N ratio < 12, WSC < 1%, NH4+–N < 400 mg kg−1, NH4+–N/NO3-–N < 0.2, WSC/TN, WSC/organic-N < 1. On the basis of these indicators, the AC method generally enhanced maturity faster than the AO, PC and PO methods. Pit methods require less investment and are recommended for the smallhold farmers.