Nitrous oxide and methane emissions following application of animal manures to grassland

Nitrous oxide (N2O) and methane (CH4) emissions were measured from grasslan d following manure applications at three times of the year. Pig (Sus scrofa ) slurry and dairy cow (Bos taurus) slurry were applied in April, at equal rates of ammoniacal-N (NH4+-N), and in July, at equal volumetric rates (50 m(3) ha(-1)). In October, five manure types were applied to grassland plots at typical application rates: pig slurry, dilute dairy cow effluent, pig f arm yard manure (FYM), beef FYM and layer manure. Emissions were measured f or 20, 22, and 24 d, respectively. In April, greater cumulative emissions o f N2O-N were measured following application of dairy cow slurry (1.51 kg ha (-1)) than pig slurry (0.77 kg ha(-1)). Cumulative CH4 emissions following application in April were significantly greater from the dairy cow slurry t reatment (0.58 kg ha(-1)) than the pig slurry treatment (0.13 kg ha(-1)) (P < 0.05). In July, significantly greater N2O-N emissions resulted from pig slurry-treated plots (0.57 kg ha(-1)) than dairy cow slurry-treated plots ( 0.34 kg ha(-1)). Cumulative net CH4 emissions were very low following July applications (<10 g ha(-1)). In October, the lowest N2O-N emission resulted from application of dilute dairy effluent, 0.15 kg ha(-1), with the greate st net emission from the application of pig slurry, 0.74 kg ha(-1). Methane emissions were greatest from the plots that received pig FYM, resulting in a mean cumulative net emission of 2.39 kg ha(-1).