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Dairy Farm Contributions To GHG Emissions

20 July 2011

US - US Department of Agriculture (USDA) scientists have produced the first detailed data on how large-scale dairy facilities contribute to the emission of greenhouse gases.

The research was conducted by Agricultural Research Service (ARS) scientists at the ARS Northwest Irrigation and Soils Research Laboratory in Kimberly, Idaho.

ARS soil scientist April Leytem led the year-long project, which involved monitoring the emissions of ammonia, carbon dioxide, methane and nitrous oxide from a commercial dairy with 10,000 milk cows in southern Idaho.

. The animals were mostly mature Holsteins that consumed a total mixed ration and produced an average of 75 pounds of milk per cow per day.

"We’ve calculated some of the first on-farm emission rates for western large-scale dairies, along with emissions per cow and per unit of milk production,” says Ms Leytem.

“We’re performing these studies on working commercial dairies, not on experimental farms.”

The facility had 20 open-lot pens, two milking parlors, a hospital barn, a maternity barn, a manure solid separator, a 25-acre wastewater storage pond and a 25-acre compost yard.

Concentration data was collected continuously for two to three days each month, along with air temperature, barometric pressure, wind direction and wind speed. After this data was collected, Leytem's team calculated the average daily emissions for each source area for each month.

The results indicated that, on average, the facility generated 3,575 pounds of ammonia, 33,092 pounds of methane and 409 pounds of nitrous oxide every day. The open lot areas generated 78 per cent of the facility's ammonia, 57 per cent of its nitrous oxide and 74 per cent of the facility's methane emissions during the spring.

In general, the emission of ammonia and nitrous oxide from the open lots were lower during the late evening and early morning, and then increased throughout the day to peak late in the day. These daily fluctuations paralleled patterns in wind speed, air temperature and livestock activity, all of which generally increased during the day. Emissions of ammonia and methane from the wastewater pond and the compost were also lower in the late evening and early morning and increased during the day.

“These studies will help producers meet air quality standards and help regulators determine what the standards should be.

“Dairy producers have been very supportive of this work,” Ms Leytem adds. “Now we want to start improving models that state and federal regulators can use to generate estimates for on-farm emissions from commercial dairy facilities.

Results from the study were published in the Journal of Environmental Quality.

Read more about this work in the July 2011 issue of Agricultural Research magazine.

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