Alberta Agriculture recommends the following practices to reduce methane emissions from manure:
Livestock produce some of the greenhouse gases attributed to global warming, and cattle are among the highest contributors.
Expelled gases are the biggest culprits, though manure itself is also a factor.
However, given the amount of manure that is produced, an estimated 20 kilograms per animal per day, its contribution to accumulated greenhouse gases is relatively low.
Manure produces methane and nitrous oxide, but the timing and amount are variable, depending on various factors, said Agriculture Canada senior research scientist Xiying Hao.
“If it is very wet manure, you have a trace of methane emissions,” she said.
“As long as you have quite a bit of water in the manure, you will always have a trace of methane. Most times with fresh manure, in the feedlot, you don’t see significant N2O emission.”
Hao has done numerous studies on feedlot cattle manure, much of it relating to greenhouse gas emissions and compost.
She has verified that animal diet, pH, type of bedding, storage and management all affect the amount of greenhouse gases that manure will produce.
Feedstuffs that slow the conversion of protein in the gut allow cattle to extract more nutrition, but results are mixed on whether that translates to lower greenhouse gas amounts in resulting manure.
Manure that has a higher pH will have higher ammonia loss, so a lower pH is more desirable, said Hao.
Typically, manure has too much phosphorus and not enough nitrogen to be an ideal fertilizer. More nitrogen is retained in the manure and it is more valuable as fertilizer if the pH is lowered through feeding practices.
Bedding also alters the pH and nitrogen-phosphorus ratio in manure.
“Typically in a feedlot, if you do use bedding, you use cereal straw and the pH is a bit higher … compared to wood chips,” said Hao.
“Wood chips are much more acidic, so you lower the pH and more nitrogen will be retained in the manure. When you apply it to crop production, you need less nitrogen supplement.”
There is no significant difference in greenhouse gas emissions when manure produced with different bedding materials is composted, so Hao deems wood chip use to be a win-win situation, while acknowledging that producers are guided first by cost when choosing bedding material.
“It’s economic driven, but we do see that other benefit with it,” she said about wood chips.
Greenhouse gas emissions depend on the amount of nitrogen once manure is applied to soil.
“Whenever you have excess nitrogen in the soil, when conditions are right, then you will have N2O emission,” Hao said.
Methane is not an issue when manure is applied to soil.
Hao’s studies have included the effect of feeding dried distillers grain on manure and emissions, as well as feeding digestate from biofuel production.
She said composting does not reduce greenhouse gas emissions from manure, although it has other advantages.
“Composting is not so green in terms of methane emissions,” she said. “Some people say composting is a measure to reduced greenhouse gas emissions. That’s not true. But with composting, you do reduce the volume, reduce the weight, reduce the moisture.”
- Apply manure to soil as soon as possible because storage encourages anaerobic decomposition, which increases methane emission.
- Avoid manure application when the soil is extremely wet.
- Avoid adding straw to manure because it is a food source for anaerobic bacteria, which produce methane.
- Choose livestock with good feed conversion.
- Increase digestibility of feed through processing so feed stays longer in digestive tract.
- Feed ionophores that reduce methane production.
- Add edible oils to feed, such as canola.
- Feed livestock based on sex, age and growth stage to match diet to nutritional requirements.
- Apply manure shortly before crop growth so maximum nitrogen is available.
- Avoid applying manure in late fall and winter, which increases emissions and nitrogen loss in spring.
- Avoid manure application in hot, windy conditions.
- Manage soil and water to improve drainage, avoid soil compaction and increase aeration.
- Spread manure evenly and avoid excess.