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1205
Estimating farm-gate ammonia emissions from Canadian beef production in 1981 as compared with 2011
The quantity of beef produced per animal in Canada over the past three decades has increased significantly as a result of improvements in production efficiency and increases in carcass weights. This resulted in a decline in greenhouse gas emissions per kilogram beef. As NH3 volatilization from beef cattle manure is also a major environmental concern, the present study compared the NH3 emissions of Canadian beef production in 1981 and 2011. A nation-wide mass balance approach based on total ammoniacal nitrogen (TAN) content in animal manure was used to estimate NH3 losses from housing, grazing, manure storage and land spreading. Temporal and regional differences in cattle categories, feed types and management systems, average daily gains and carcass weights were considered. On average, 21% to 22% of the total nitrogen (N) consumed by Canadian beef cattle was lost as NH3-N in both years. Highest losses were observed in finished cattle where approximately 43% of the N consumed was lost as NH3-N. Contribution of NH3 from the various cattle classes differed between years and was mainly due to differences in the type of feeds used, and proportions of breeding stock and cattle finished in feedlots. Emission sources were generally consistent in both years, with average values of 12%, 40%, 28% and 21% associated with animal housing, animal grazing, manure storage and land spreading, respectively. Total NH3 emissions from the production of Canadian beef cattle (standardised on the basis of the size of the breeding herd within the reference year) was 27% higher in 2011 than they were 1981. The average emissions per animal in 1981 and 2011 were 14.2 and 15.7 kg NH3/animal/yr, respectively. On an intensity basis, however, kilogram of NH3 emitted per kilogram of beef decreased by 20%, from 0.17 in 1981 to 0.14 in 2011. The reduction in NH3 intensity is mainly attributed to increase in reproductive efficiency, average daily gain and slaughter weights, and the resulting improvement in productivity per breeding herd over the study period. Differences in intensity may also be attributed to increased use of extended grazing (e.g., swath, stockpiled and bale grazing) in 2011 compared to 1981. As management practices are altered in response to changes in profitability and policy, further studies are necessary to assess the impact of the beef industry on NH3 emissions and air quality at the local, regional and national scale.
Keywords: ammonia emission intensity, beef, Canada.