Amelioration of Composting Process by Fertilizers

Abstract

Six different composts, four of them produced from oil palm residues and two commercial composts, were studied for their stability and quality. The composts were analyzed for their total C, total N, C/N ratio, mineral N, nitrogen mineralization index, CO2 production, biomass C, specific respiration rate, germination rate, pH values and plant growth index. Composts of oil palm (Elaeis guineesis) trunk and oil palm empty fruit bunch treated with N and P showed good stability and higher quality as compared to other composts. Their C/N ratios were the lowest (14-18) but their pH values were comparatively low (4.6-6.4). They had a good amount of total N (0.95-1.84%) with higher nitrate than ammonium nitrogen. The specific respiration rates were very low (0.25-0.63) which is an indication that these two composts are stable. Plant growth test supported conclusions based on the microbiological tests. Their properties were considered as suitable for planting media application. Compost quality can be further improved by adding bunch ash, which has high values of pH and is also a by-product from the oil palm industry. The applied nitrogen mineralization index could not be used with all kinds of composts as stability index. Both of the commercial composts showed high C/N ratios (34-68) and very low values of total and mineral nitrogen compared to oil palm residues composts. They were considered having low nutritional value and not recommended for planting media application.