Changes during processing in the organic matter of composted and air-dried poultry manure

Abstract

Composting and active drying are the main techniques employed to prevent losses of NH 3 and development of undesirable odours from poultry manure. We studied the effects of these treatments on C and N content and stabilization of organic matter. Carbon and N contents of composted poultry manure (CPM) at the end of the processes were 82.9 and 56.1%, respectively, of the initial material, whereas the C content of dried poultry manure (DPM) remained practically the same, while the N content slightly increased with time. Nitrogen content of DPM at the end of the process was about three times higher than that of CPM (55.1 and 19.2 mg/g, respectively). The humification index (HI) showed a decreasing trend in both products, indicating the formation of humic substances in both processes, although to different extents: even at 20 days CPM showed HI values typical of a well-matured material (0.50), whereas HI for DPM at the end of the process was 1.14, indicating that this material did not achieve stabilization. Application of electrofocusing (EF) to characterize the qualitative evolution of humic substances showed a more complex EF profile in the case of CPM and confirmed the higher stabilization of OM in the composted material. CPM could be useful as a soil amendment because of its high degree of stabilization, whereas DPM can be considered mainly as an organic fertilizer, because of its high content of N. If DPM was piled for a long period its OM could achieve a high degree of humification, so increasing the agronomic quality of this fertilizer.