|Turner, Kenneth - Ken|
|COLE, NOEL - Retired ARS Employee|
Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 5/27/2016
Publication Date: 6/14/2016
Citation: Todd, R.W., Moffet, C., Neel, J.P., Turner, K.E., Steiner, J.L., Cole, N.A. 2016. Pasture-scale methane emissions of grazing cattle. Proceedings of the Great Plains Grazing Field Research Symposium, June 14, 2016, Stillwater, OK. p.46.
Interpretive Summary: Research on grazing cattle improves estimates of methane emission. Methane is a gas that contributes to global warming. It is a major part of the greenhouse gases that U.S. agriculture adds to the atmosphere. Cattle are a source of methane, so we wanted to better understand how much methane grazing cows produce. A team of ARS scientists from Bushland, TX, Woodward, OK and El Reno OK used three different methods to measure the methane from cattle grazing a native pasture in central Oklahoma. They found that the three methods were in close agreement, with each cow-calf pair emitting from 0.75 to 0.85 pounds per day. They concluded that a 1000 pound cow with a calf grazing early season Oklahoma pasture (called an animal unit) would produce 0.52 pounds of methane per day. Regulators can use this information to improve inventory estimates. This research gives scientists data to check computer programs that predict methane emissions. These results contribute to a better understanding of the role of cattle in greenhouse gas emissions.
Technical Abstract: Grazing cattle are mobile point sources of methane and present challenges to quantify emissions using noninterfering micrometeorological methods. Stocking density is low and cattle can bunch up or disperse over a wide area, so knowing cattle locations is critical. The methane concentration downwind of a herd may only increase slightly above upwind concentration, so that careful concentration measurements are needed. The objective during an intensive field campaign of summer 2014 was to use a micrometeorological method to quantify pasture scale methane emissions from grazing cattle. Study pasture was a 26.4 ha tallgrass prairie at El Reno, Oklahoma grazed by 50 cow calf pairs. Each beef cow was fitted with a GPS tracking unit. Three open path methane lasers on motorized positioners scanned 16 paths that crisscrossed the pasture. Sonic anemometers measured wind speed and direction and variances of wind components. We used dispersion analysis to model methane dispersion from the cattle. After quality control filtering, retention of quarter-hour emission data was 24% during five days. Best quality data were acquired when cows were least active. Most per capita emission rates ranged from 150 to 600 grams of methane per day per cow calf. Mean emission rate for five days during the campaign was 359 +/- 61 grams of methane per day per cow calf, which included a negligible soil source/sink. Independent, concurrent measurements from two GreenFeed systems and an Intergovernmental Panel on Climate Change Tier 2 estimate of enteric methane emission were 385 +/- 57 and 340 +/- 57 grams of methane per day per cow calf, respectively. Methane emission of the cow-calf pair as a fraction of body weight for the three methods ranged from 0.49 to 0.56 grams of methane per day per kilogram of body weight. We concluded that a reasonable estimate for enteric methane emissions from beef cows with calves grazing early season tallgrass prairie was 0.52 +/- 0.11 grams of methae per day per kilogram of body weight.