Loss of nitrogenous compounds during composting of animal wastes

The nitrogen losses occurring during composting of mixtures of straw and different liquid manures (poultry, pig, cattle, and mixtures thereof) over a period of 98 to 114 days have been determined. During the composting period between 9·6 and 19·6% of the initial total nitrogen was lost as leachates. Most of the leaching (>70%) occurred within the first 10 days of the composting period. Consequently, large amounts of nitrogen are carried out of the compost with the leachate over this period largely as a result of the high nitrogen concentrations. The greatest proportion of nitrogen in the leachate (76·5−97·8%) was ammonium-nitrogen. The greatest nitrogen losses, between 46·8 and 77·4% of the initial total nitrogen content, were caused by gaseous emissions in the form of NH3 as well as small amounts (<5%) of NOx. The main factors which influenced the level of gaseous emissions were the total nitrogen content at the beginning of the composting period, the temperature of the compost material and heap rotation (turning). The greatest nitrogen losses were found in the N-rich poultry- and pig-straw mixtures which showed obvious temperature increases up to 40°C during the first few days of the composting period. A high pH value (pH>8) promoted the gaseous NH3 emission which is important from an environmental perspective.