Besides making milk, dairy cattle also generate more manure (62 kg per day) than other types of cattle, according to the University of Guelph, citing Statistics Canada data.
Proper manure management can help reduce the environmental impact of dairy cows and improve agricultural sustainability, said Jeff Wood, a recent doctoral graduate from the University of Guelph School of Environmental Sciences.
Although gases such as methane, nitrous oxide and ammonia occur naturally in manure, they can harm the environment, Wood said.
Methane and nitrous oxide are both greenhouse gases.
When ammonia ends up in aquatic or soil systems, it can cause eutrophication — excessive plant growth from too many nutrients — and acidification. A number of aquatic plants and animals are susceptible to ammonia toxicity.
For his thesis, Wood looked at ways to reduce gas emissions from liquid manure storage systems on farms.
"One issue is that there are times when farmers have to store manure for an extended period," he said. "This is because either the land base can't support continuous spreading or the weather conditions will not permit spreading."
When soil is frozen, for example, manure cannot be applied because it is more likely to run off into surface waters.
Farmers often store liquid manure until the conditions are appropriate for spreading, but storing it for a long time leads to anaerobic decomposition, which results in gas emissions, Wood said.
Wood studied the concentration of organic matter in liquid manure — measured by the level of solids — and how that was related to emissions. These solids can be traced back to what the animal ate as well as its bedding material. He found that higher concentrations of solids yielded higher gas emissions.
His research showed that lowering the amount of solids in manure decreased emissions.
"The most practical approach would be solid/liquid separation," Wood said, adding that further research is needed to better understand emissions from both the solid and liquid components.