Greenhouse gas emission from stored livestock slurry

Animal manure contributes about 40% of the total methane (CH4) and 20% of the total nitrous oxide (N2O) emissions in Denmark. We measured the CH4 and N2O emissions from stored cattle slurry and fermented slurry during fall 1996 and summer 1997 and evaluated the effect of surface covers consisting of straw, floating leca pebbles, or a natural surface crust on the patterns of these emissions. No emission of N2O was measured during periods with more rain than evaporation from the slurry stores and no emission was measured from uncovered slurry, irrespective of climatic conditions. During the summer storage with drying conditions, N2O emissions of up to 25 mg N m(-2) h(-1) were recorded from slurry with surface covers. Total N2O emission was highest from digested slurry. The emission of CH4 from stored fermented slurry and cattle slurry varied between <0.01 and 1.4 or 0.7 g CH4-C m(-3) h(-1), respectively. The log-transformed emissions were linearly related to the inverse temperature. Emission of CH4 was reduced, on average, by 38% with surface covers. The reduction was probably due to CH4 oxidation in the surface revers or in the interface between the cover and liquid in the store. Fermentation did not reduce CH4 emissions during storage of the slurry.