Characterisation of organic matter and nutrients during composting of livestock manure.

The properties of livestock manure during composting were studied in order to understand the changes in physical and chemical composition. The composting was carried out in a commercial organic fertilizer plant utilizing an aerobic process, and the following parameters were measured in samples collected at different stages of composting: moisture content, temperature, total C, humic substance (HS) contents and fractions - fulvic acid (FA) and humic acid (HA), macro-and micro-nutrients. Correlation analysis was carried out between these manure properties. Total C and N concentrations declined by 22 and 19%, respectively in the final manure at the end of composting. During composting, Kh progressively became the dominant fraction of HS. Phosphorus levels increased by 21%, K and Mg by 11% each, and Ca by 12% respectively. The C/N ratio declined only slightly from the initial value of 14.8 to 13.4 after composting. In terms of micronutrients, the compost was highest in Fe and lowest in Cu content. Total C had highly significant positive correlations with N and FA, while N had a highly significant negative correlation with Mg. Among the micronutrients, only Mn had significant positive or negative correlations with the HS fractions. Since the concentration of N tends to decline during aerobic composting, it might be necessary to supplement the manure with inorganic sources, depending on soil nutrient status and crop requirements.