11 September 2009

3 minute read

North America

That's according to Alvaro Garcia, a South Dakota Cooperative Extension Dairy Specialist, who recommends a three-part approach to reduce odour emissions.

“Producers should create a list of potential odour sources on the farm, then determine the sources most likely to bring complaints,” Mr Garcia said. “Then it is a matter of listing control strategies for each odour source.”

Odour control practices can aim at reduced generation, decreased emission, and/or increased dispersion.

“Dietary modifications that result in reduced ammonia generation should be considered best management practices,” Mr Garcia said. “Those practices include adequately balancing diets, feeding highly digestible feedstuffs, and preserving feeds adequately.”

Mr Garcia said that a recent study conducted by the Wageningen Research Centre in the Netherlands studied the effect of diet on ammonia emissions from dairy cow barns. This trial also evaluated the usefulness of testing for milk urea as an indicator of emission reduction.

During this experiment, Holstein cows were housed in confinement and were fed a diet that consisted of ensiled forages and concentrates. Cows were offered rations that contained rumen-degradable protein balanced at 0, 1.1, and 2.2 pounds per cow, per day.

Ammonia emissions from the barn increased with higher levels of rumen-degradable protein balance in the diet. Bulk tank milk urea and temperature were highly correlated with ammonia emissions from the barn, accounting for 76 per cent of the variation in emission.

Temperature appears to have a positive correlation with ammonia emission. Ammonia emission from the barn increased 2.7 per cent when outdoor temperatures increased by 1.8 degrees F.

The study concluded that the emission of ammonia from naturally ventilated dairy cow barns was strongly influenced by the diet. The emission can be reduced approximately 50 percent by reducing the rumen-degradable protein balance of the ration from 2.2 to zero pounds per cow per day.

Testing for milk urea nitrogen (MUN) can be a useful and relatively inexpensive tool to monitor if rumen degradable protein is fed in excess of requirements.

Another approach to mitigate odor is through reduced emissions. Manure lagoons covered with inorganic plastic covers have the advantage of higher nutrient retention and considerable odor control effectiveness when properly managed. To make the most of these covers care should be taken during agitation and pumping.

Linde Dairy of White, South Dakota, has begun construction of such a lagoon cover over the first stage of the dairy's manure lagoon system to control odours and greenhouse gases. The project, the first of its kind in South Dakota, is a partnership between Linde Dairy, Environmental Credit Corp. (ECC), headquartered in Ithaca, New York, and Environmental Capital Management (ECM), a private hedge fund, based in Tempe, Arizona.

Through ECC's Ag-Methane Lagoon Cover Programme, the cost of installing the cover system will be paid for through the creation and sale of carbon credits from the captured and destroyed methane.

Carbon credits are a form of pollution credit purchased by utilities and manufactures as a way to pay for reductions of greenhouse gases at a lower cost.

Dairyman Rein Landman milks 1,050 cows at his modern dairy. He sees this project as “something for the future and for taking care of the environment.”

Methane contributes to the greenhouse effect at a rate 21 times greater than carbon dioxide. The dairy shares the revenue from the project and gets a cheap source of renewable biogas after the system has some time to work. “I'm interested in catching the methane and using it for the dairy,” Mr Landham said.

“The project will also offer other benefits including odour reduction, storm water protection, pest control, and reduced liability.”

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