Methane Emissions From Dairy Cattle and Liquid Manure Measured Using an Inverse Dispersion Technique.

Farm-scale emission measurements are useful for assessing emissions under actual farm conditions. A recent assessment of the IPCC Tier 2 livestock methane emission model identified that the national methane emission estimates for enteric fermentation had an uncertainty of 38% and manure management had an uncertainty of 73%. Furthermore, this analysis identified that uncertainty can be reduced by disaggregating key model parameters regionally and according to animal subcategories. To accomplish this, regional emission factors should be developed, which requires regional emission measurements from animals and manure storages.

In this work we measured CH₄ emissions from two dairy farms in Eastern Ontario. Both farms had Holstein-Friesian cattle and liquid manure stored in earthen basins. The farms were selected for suitability with the bLS inverse dispersion technique, e.g., flat terrain and absence of upwind CH₄ sources. To capture seasonal changes and management effects, measurements were conducted during multiple seasons, and when the manure storages were full and empty. The building configuration at one farm allowed independent measurement of emissions from the manure storage and the animals. With these observations we present diurnal and seasonal changes, the relative emissions from manure versus enteric sources, and compare measured emissions to the IPCC enteric and manure methane models.