More than 50% of the protein-nitrogen fed to beef cattle can escape annually to the atmosphere as ammonia gas, according to a USDA-led study of two Texas cattle feedyards, and emissions increase when cattle diets contain wet distillers grains, a byproduct of corn-ethanol production.
The findings, which appear in the current issue of the Journal of Environmental Quality, suggest that fine-tuning cattle diets could therefore be the best option for minimizing feedyard losses of ammonia—which besides its pungent smell contributes to environmental problems such as acid rain, nutrient pollution, and smog.
However, the solution could also be a challenging one for cattle producers, says the study’s leader, USDA-ARS research soil scientist Richard Todd. “They face a feed supply environment that’s increasingly dominated by the growing demand for corn-based ethanol.”
Ammonia production by large dairy farms and cattle feedyards is a mounting air quality concern. The EPA already requires most feedyards to report their ammonia emissions under the Emergency Planning and Community Right-to-Know Act, and a coalition of citizen groups petitioned the agency last April to begin regulating ammonia under the Clean Air Act, as well.
While several studies have reported ammonia emissions over short time periods, however, there has been no multi-year, multi-location research to quantify emissions. To fill this gap, USDA-ARS scientists from the Conservation and Production Research Laboratory in Bushland, TX, collaborated with researchers at West Texas A&M University and Texas AgriLife Research on a two-year study in the heart of the cattle-feeding industry: the Texas Panhandle. The research was funded by a grant from the USDA National Institute of Food and Agriculture (NIFA).
From March 2007 to February 2009, the researchers continuously operated tuned-diode, open-path lasers to measure atmospheric ammonia concentration at two feedyards, while also making an array of meteorological measurements. The data were then used in an inverse dispersion model to quantify ammonia emissions.
Not surprisingly, patterns of ammonia emissions tracked annual temperature patterns closely, with the greatest losses occurring during summer and the smallest in winter. During winter, 42% and 44% of fed nitrogen was lost as ammonia at the two feedyards, while in summer losses reached 68% and 71%. Averaged over the two years of the study, 52% and 59% of fed nitrogen was lost as ammonia at the two locations, or 80 and 115 grams of ammonia-nitrogen per animal per day.
Because ammonia emission is sensitive to crude protein in cattle rations, it also rose when one of the feedyards fed diets that included wet distillers grains, whose crude protein content can greatly exceed the nutritional needs of cattle. As a result, excess nitrogen was excreted in urine and feces, and then lost as ammonia, producing emissions that sometimes topped 200 grams per animal per day.
While the findings suggest that feeding cattle distillers grains from corn-ethanol production will complicate efforts to reduce feedyard ammonia losses, the authors also caution that considerable variability existed both within and between the two sites they examined. More detailed studies are needed, they say, to better understand the impact of management and environmental variables, such as diet, temperature, precipitation, and manure water content, on feedyard ammonia emissions.
Material summarized from:
Daily, Monthly, Seasonal, and Annual Ammonia Emissions from Southern High Plains Cattle Feedyards
Richard W. Todd, N. Andy Cole, Marty B. Rhoades, David B. Parker and Kenneth D. Casey
Journal of Environmental Quality
Photo courtesy of USDA-ARS