Scientists measure various gases of 13,000-cow dairy

By CAROL RYAN DUMAS

Capital Press

A yearlong study of greenhouse gas emissions on an Idaho dairy with 10,000 milking cows has provided scientists insight into greenhouse gas emissions produced by large-scale Western dairies.

"We're just trying to get a baseline, how much we'd expect to see on an open lot or freestall dairy," said April Leytem, lead scientist on the project performed by USDA Agricultural Research Service's Northwest Irrigation and Soils Research Laboratory, in Kimberly, Idaho.

The team measured methane, nitrous oxide, carbon dioxide, and ammonia from the dairy's 13,000 animals and manure-handling operation.

While ammonia is not a greenhouse gas, ammonia is typically factored into greenhouse gas levels because it is often a secondary source of nitrous oxide, Leytem said.

The study found that the dairy produced 3,582 pounds of ammonia, 33,162 pounds of methane, 410 pounds of nitrous oxide and 713,831.5 pounds of carbon dioxide each day.

The Environmental Protection Agency has issued a rule mandating that livestock facilities report methane and nitrous oxide emissions if they have manure management systems that emit 25,000 metric tons, or 55.1 million pounds, of carbon dioxide equivalent gases.

CAFOs are also required to report ammonia emissions if they exceed a certain level under the Emergency Planning and Community Right-to-Know Act.

The problem is few studies have measured emissions on dairies, Leytem said. The current study is the lab's second on emissions. Another on wastewater ponds is in the works.

"We're getting pretty confident with what you'd expect from a farm. Our numbers are consistent among dairies, small or big, and with other studies," she said.

The studies should benefit both farmers and regulators.

"These studies will help producers meet air-quality standards and help regulators determine what the standards should be," said Dave Bjorneberg, ARS ag engineer on the project.

For example, the EPA estimates that 3,200 mature dairy cows produce the 25,000 metric tons of annual carbon dioxide equivalent that would trigger reporting requirements. The ARS study, however, equates that emissions threshold at 4,808 mature cows, based on the dairy it monitored.

"The advantage of this study is it pertains to Idaho," said Bob Naerebout, executive director of Idaho Dairymen's Association, which helped fund the study. "It's based off of real, actual Idaho climate and what exactly is going on in Idaho."

Evaporation rates, humidity, moisture and heat all impact emissions, he said. Conditions in Idaho are not the same as in other dairy states.

"All information should be, particularly if regulation is involved, based on peer-reviewed science," he said.

The Innovation Center for U.S. Dairy is also interested in ARS's work with emissions.

"We need unbiased, peer-reviewed science to be able to really assess the impact and so we're all looking at the same number," said Erin Fitzgerald, the Center's vice president of sustainability.

There are misperceptions about dairy's impact on the environment and consumers are increasingly demanding environmentally friendly milk, she said.

Such studies provide evidence of dairymen's good environmental stewardship and provide tools to become even more efficient, she said.