Manure methane emissions over three years at a swine farm in western Canada

Swine manure is kept in outdoor storage facilities until it is applied to cropland. Anaerobic conditions facilitate microbial methane (CH₄ ) production at a rate that depends on temperature. Manure CH₄ emissions can be the largest contributor to the carbon footprint of pork production. Despite the importance of CH₄ , its actual emissions in cold temperate climates are highly uncertain. This study measured emissions from a single-cell earthen manure storage facility at a commercial swine farm near Brandon, Manitoba, Canada, for 3 yr. Complimentary laboratory measurements were done to assess CH₄ potential (B₀ ). The manure storage regularly received manure from the barn and was only emptied in October. In the summer, manure temperature was usually lower than the air temperature, with the manure temperature (averaged across depths) warming to between 15 and 18.5 °C for only 9 wk. Emissions of CH₄ were low, with the CH₄ conversion factor being between 3.0 and 11.0%, depending on the year (using the IPCC 2019 default B₀ ). Scaled by the number of swine reaching market weight (125 kg) each year, CH₄ emissions were between 250 and 902 g CH₄ animal^-1 . Laboratory measurements of CH₄ production potential scaled by VS were 335 ml CH₄ g^-1 VS at 37 °C, perhaps lower than the IPCC 2019 default value due to barley (Hordeum vulgare L.) in the ration and degradation in the under-barn pit prior to transfer outdoors. Taken together, the low manure temperatures, short warm season, and barley in the ration suggest that emissions from swine manure in cold climates like western Canada are considerably lower than previously estimated based on default factors.