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 (CH 4 ) production at a rate that depends on temperature. Manure CH 4 emissions can be the largest contributor to the carbon footprint of pork production. Despite the importance of CH 4 , 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 CH 4 potential (B 0 ). 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 CH 4 were low, with the CH 4 conversion factor being between 3.0 and 11.0%, depending on the year (using the IPCC 2019 default B 0 ). Scaled by the number of swine reaching market weight (125 kg) each year, CH 4 emissions were between 250 and 902 g CH 4 animal -1 . Laboratory measurements of CH 4 production potential scaled by VS were 335 ml CH 4 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.