Nitrous oxide emissions and soil mineral nitrogen status following application of hog slurry and inorganic fertilisers to acidic soils under forage grass

Abstract

Field application of livestock slurry often results in higher nitrous oxide (N2O) emissions than inorganic fertiliser, because slurry contains large amounts of available N and C, and when applied it increases soil water content, thus enhancing denitrification. This study evaluated the impact of hog (Sus scrofa) slurry and inorganic fertilisers on N2O emissions and soil inorganic N. Three short-term (3 wk) field experiments were conducted during summer 2005 on two contrasting acidic soils seeded to forage grass. Treatments included hog slurry (Slurry) at 126 kg N ha-1, potassium nitrate (Nitrate) at 120 kg N ha-1, ammonium sulphate (Ammonium) at 120 kg N ha-1, Carbon (Dextrose) at 500 kg ha-1 and an unamended control (Control). Potassium nitrate increased (P< 0.05) cumulative N2O losses compared with the other treatments. Emissions of N2O from Slurry and Ammonium were similar, but higher than from Dextrose and Control, which were similar. Soil NH4+-N contents for Slurry and Ammonium treatments were generally similar but higher than for the other treatments, particularly during the first and second sampling dates. Soil NO3−-N contents, meanwhile, were higher with the Nitrate treatment compared with the other treatments, especially at the first sampling date. These results imply that N2O production in these acid soils was limited by NO3-availability. Therefore, N2O emissions from these soils can be minimised by using ammonium-based fertilisers including hog slurry rather than nitrate-based fertilisers. Key words: Acidic soils, hog slurry, mineral fertiliser, soil nitrogen, N2O emissions