|Hristov, Alex -|
|Hanigan, Mike -|
|Mcallister, Tim -|
|Ndegwa, Pius -|
Submitted to: Canadian Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 2, 2010
Publication Date: March 1, 2011
Citation: Hristov, A., Hanigan, M., Cole, N.A., Todd, R.W., McAllister, T., Ndegwa, P., Rotz, C.A. 2011. Review: Ammonia emissions from dairy farms and beef feedlots. Canadian Journal of Animal Science. 91:1-35. Interpretive Summary: Livestock feeding operations are a major source of ammonia in the atmosphere. Ammonia released from animal feeding operations is a potential environmental and human health hazard, potentially causing degradation of aquatic systems, and formation of fine particulate matter. It is also a loss of valuable nitrogen (N) which lowers the fertilizer value of the manure. This manuscript provides a review of ammonia emissions and the processes involved in ammonia emission from dairies and beef cattle feedlots typical of North America. Ammonia emissions from cattle operations result from complex interactions of factors such as diet, manure management, temperature, wind speed, turbulence, and manure composition. The primary source of ammonia losses is urinary urea. Many methods have been used to estimate ammonia emissions. Existing data on ammonia emission factors and flux rates are extremely variable, in part because of the different methods used. A total nitrogen balance for a feed yard or dairy is important to corroborate estimated emissions. For dairy farms, reported emission factors from 31 studies range from 0.82 to 250 grams of ammonia per cow daily, with an average of 59 grams per cow per day. Ammonia flux rates for dairy farms averaged 1.03 grams m**2 per hour. Ammonia losses are somewhat greater from beef feedlots. Emission factors from nine studies averaged 119 grams per animal daily, with a summer high of 280 grams per animal daily. Ammonia flux rate for beef feedlots averaged 0.174 grams m**2 per hour. Using nitrogen mass balance approaches, daily ammonia nitrogen losses from dairies and feedlots have ranged from 25 to 75% of the nitrogen excreted. Ammonia emission can be decreased at various segments of the production system. Reducing dietary crude protein concentration and/or decreasing the ruminal degradability of the protein can reduce emission potential and whole-farm ammonia emissions. Interventions to decrease ammonia emissions, however, must be balanced with potential adverse effects on production. Sustainable dairy and beef cattle production that minimizes environmental impacts will require technologies and practices that reduce ammonia emissions.
Technical Abstract: Ammonia emitted from animal feeding operations is an environmental and human health hazard, causing water eutrophication, and fine particulate matter formation, and at the same time is a net loss of manure fertilizer value. A significant portion of cattle manure nitrogen, primarily from urinary urea, is converted to ammonium and eventually lost to the atmosphere as ammonia. Determining ammonia emissions from cattle operations is complicated by the multifaceted nature of the factors regulating ammonia volatilization such as manure management, ambient temperature, air velocity, and manure composition, and pH. It is also of interest to determine the ammonia emitting potential of manure (AEP) independent of environmental factors. The ratio of nitrogen to non-volatile minerals (phosphorus, potassium, ash), or nitrogen isotope ratio in manure have been suggested as useful indicators of AEP. The existing data on ammonia emission factors and flux rates are extremely variable. For dairy farms, emission factors from 0.82 to 250 g ammonia per cow per day have been reported, with an average of 59 g/cow per day (n = 31). Ammonia flux rates for dairy farms averaged 1.03 g/m**2 per hour (n = 24). Ammonia losses are significantly greater from beef feedlots. Emission factors averaged 119 g/animal per day (n = 9) and could be as high as 280 grams per animal per day. Ammonia flux rate for beef feedlots averaged 0.174 g/m**2 per hour (n = 12). Using nitrogen mass balance approaches, daily ammonia nitrogen losses of 25 to 75% of the nitrogen excreted with manure have been estimated for dairy cows and feedlot cattle. Ammonia emission can be mitigated at various segments of the production system. Reducing crude protein concentration in cattle diets and ruminal protein degradability are powerful tools for reducing AEP and whole-farm ammonia emissions. Reducing dietary protein would also benefit the farmer by reducing feed cost. These interventions, however, have to be balanced with the potential risk for loss of production. Mitigating ammonia emissions from dairy and beef cattle operations is becoming critical for achieving sustainable animal production and will benefit producers as well as the society in general.