Loss of Nitrous Oxide from Animal Manure in Dungheaps

Concentrations of N2O in gas samples taken from dungheaps of cattle and pig manure were up to 100 times greater than the atmospheric concentration. The concentrations varied little with time but tended to increase with depth. The concentrations were less in fresh manure than in stored manure, and less in cattle manure than in pig manure. The rate of release of N2O from the manure surface was also determined. The mean rate from stored pig manure was 11 mg N2O-N m−2 h−1, which is low compared to typical total-N losses. The production of N2O is probably caused by microbial denitrification but could also arise from nitrification. The release of N2O may be accompanied by a greater release of N2, as the conditions in manure favour the denitrification process going to completion.