Emissions of ammonia and nitrous oxide following incorporation into the soil of farmyard manures stored at different densities

Before spreading to land, farmyard manures (FYM) from pigs (Sus scrofa) and beef cattle (Bos taurus) were stored, for c. 120-150 days, either uncompacted or compacted. Compaction was carried out as the manures were put into store and the compacted manures were covered with plastic sheeting. Both compacted and uncompacted FYM were either incorporated by ploughing immediately after spreading, within 4 h, within 24 h or left on the surface until the soil was cultivated prior to planting. Despite greater amounts of total ammoniacal nitrogen (TAN) remaining in the compacted pig FYM, ammonia (NH3) emissions following spreading were not significantly greater than from the uncompacted FYM, even when left on the soil surface. Incorporation of pig FYM reduced NH3 emissions by c. 90, 60 and 30% for immediate, within 4 h and within 24 h incorporation, respectively. There were no effects of compaction during storage on nitrous oxide (N2O) emissions following spreading for the measurement period of 60 days. Incorporation had no effect on N2O emissions from pig FYM following spreading in the first experiment, but reduced emissions following spreading in the second year and reduced N2O emissions following the spreading of cattle FYM in both experiments. These results indicate that rapid incorporation of FYM after spreading to land is an effective means of reducing NH3 emissions and need not lead to increases in N2O emissions.