Nitrous Oxide and Methane Emissions following Application of Animal Manures to Grassland

Abstract Nitrous oxide (N 2 O) and methane (CH 4 ) emissions were measured from grassland 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 (NH + 4 ‐N), and in July, at equal volumetric rates (50 m 3 ha −1 ). I n October, five manure types were applied to grassland plots at typical application rates: pig slurry, dilute dairy cow effluent, pig farm yard manure (FYM), beef FYM and layer manure. Emissions were measured for 20, 22, and 24 d, respectively. In April, greater cumulative emissions of N 2 O‐N were measured following application of dairy cow slurry (1.51 kg ha −1 ) than pig slurry (0.77 kg ha −1 ). Cumulative CH 4 emissions following application in April were significantly greater from the dairy cow slurry treatment (0.58 kg ha −1 ) than the pig slurry treatment (0.13 kg ha −1 ) ( P < 0.05). In July, significantly greater N 2 O‐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 CH 4 emissions were very low following July applications (<10 g ha −1 ). In October, the lowest N 2 O‐N emission resulted from application of dilute dairy effluent, 0.15 kg ha −1 , with the greatest 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 .