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

Abstract

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 9wk. 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 (125kg) each year, CH4 emissions were between 250 and 902g CH4 animal-1 . Laboratory measurements of CH4 production potential scaled by VS were 335ml CH4 g-1 VS at 37°C, perhaps lower than the IPCC 2019 default value due to barley (Hordeum vulgareL.) 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.