Agricultural Modeling and Training Systems recently hosted a webinar, “Mitigation of Greenhouse Gas Emissions from Dairy Farms,” presented by University of Wisconsin Madison’s Michel Wattiaux.
Wattiaux said that the greenhouse gas emissions caused by milk production amounts to about 1.9% of U.S. greenhouse gas emissions.
Among farming-related emissions, manure in the field for crop production amounts to 19%, cattle themselves contribute 25% and manure management is responsible for 24%.
“We have a lot of emission coming from methane from the cow,” Wattiaux said. “It’s the single most important component followed by manure.”
What cows eat affects more than their milk output. It also affects their methane output.
“When you increase the forage proportion of the diet, you increase methane production, yield and intensity,” Wattiaux said.
He said that feed additives such as 3-nitrooxypropanol offer a way to reduce emissions from cows.
“The efficiency of the cow can help us reduce the emissions in the cow,” Wattiaux said.
Breeding for better, healthier animals may also help.
“The cow of lower efficiency produces great amounts of methane per kilo of forage digested versus cows of higher efficiency,” Wattiaux said.
He said that lower levels of microbes in the rumen of lower efficiency cows may be the reason why.
“We also found that high efficiency cows who eat a lot, the rate of passage is greater and the result of that, they have a greater loss of fecal energy,” Wattiaux said. “They have lower digestive efficiency than lower efficiency cows. The lower pheontypical efficient cows had less energy in the urine, less methane energy and less heat released by those cows. They had greater energy available for production of milk. It’s not going to be a silver bullet to fix it all.”
An average dairy cow produces about 34,500 kilograms of manure annually.
Wattiaux said that farmers who handle manure through anaerobic digestion or a combination of anaerobic digestion and solid-liquid separation “have a substantial reduction of emission of greenhouse gasses” compared with farms that only manage with solid-liquid separation.
The size of the farm also makes a difference in how they emit greenhouse gas, according to Wattiaux.
“With small farms, the greenhouse gas emissions tends to be associated with spreading,” he said. “With large farms, it’s with storage.”
He also said that soils can affect greenhouse gas emissions, including through land use, land cover, vegetation, nutrients, humidity and temperature.
“From those emission sources, the farmer doesn’t have a lot of control except the carbon/nitrogen ratio which can be changed with the application of mature or chemical fertilizer,” Wattiaux said.
He advised avoiding annual monoculture, which “results in much greater emission of nitrous oxide than perennial poly-cultures.”
Diverse rotations also enhance the effect.
Going with organic management may not have as much of an effect as farmers think it does on conservation. Wattiaux said that the greater surface area of land used to produce the same amount of milk as a conventional farm undoes some of the ecologic benefits of organic farming, although it produced the lowest level of emissions.
Wattiaux said that more research needs to look at a farm holistically.
“When you produce milk, you also produce meat,” he said. “A large contribution of the meat consumed is the U.S. comes from the dairy sector so how do we attribute emissions to beef and dairy? Many farms also output cereal crops for the human food chain. We need to look at those farmers as a whole, not just the dairy.”