Patterns of methane emission from excreta of grazing animals
Emissions of methane from dung pats under field and laboratory conditions have been determined. A range of dung materials from cattle and sheep and from cattle with different background managements was used and results indicated that all acted as significant sources of CH4 over a relatively short period, usually less than 10–15 days. The patterns of release were similar, although modified by environmental conditions. A strong exponential relationship was determined between total CH4 released and the C-to-N status of the dung, i.e. a greater rate of release with higher N status. Similar trends and patterns were displayed under controlled conditions. It was clear that the major effect came from dung itself with only a relatively small positive interaction when soil was present. Emission was stopped completely by a fumigation (chloroform)-evacuation procedure; evacuation alone (i.e. with the sample under vacuum) changed the pattern of release and increased the total amounts emitted. Although the emissions of CH4 from dung were significant, the amounts were small relative to the estimated total release from a complete livestock production system, i.e. <0.2% of the total CH4 output from a dairy farm.