Farmers’ fields an unexpected greenhouse gas producer

THAWING FARMERS’ FIELDS FUEL CLIMATE CHANGE, STUDY FINDS

Across Canada, the last of the snow and ice is melting away from a vast expanse of farmers’ fields, making way for the planting of this year’s crops. And, suggests a new Canadian study, making an unexpectedly large contribution to greenhouse gases and climate change.

Strange as it might seem, the thawing of frozen cropland burps nitrous oxide into the atmosphere at rates far greater than previously thought, meaning agriculture’s role in producing the greenhouse gas has been greatly underestimated, according to University of Guelph research.

“It was surprising to see the results,” says Ron Bonnett, president of the Canadian Federation of Agriculture. “I don’t think anyone would have expected that.”

The study’s lead author, Guelph atmospheric sciences professor Claudia Wagner-Riddle, said farmers ought to consider taking climatechange countermeasures, including leaving nitrogen-absorbing “cover crops” on their fields all winter.

While still much less of a factor than industrial sources of pollution, the greenhouse-gas spewed out by croplands shouldn’t be ignored, she said.

“It’s a side-effect of agriculture that could be addressed with some relatively simple measures,” said WagnerRiddle. “We are always going to have to eat, so this is not going to go away.”

Farmers are, in fact, concerned about their industry’s part in the climate-change phenomenon, which also includes methane emissions from livestock manure, said Bonnett.

But some of the recommended measures are costly — and could undercut Canadian producers’ competitiveness if the U.S. government does not insist on similar steps, he said.

Bonnett said farmers need incentives to take action, like the cap-andtrade system more typically associated with power plants and other fossil fuel-burning polluters.

Nitrous oxide, commonly known as laughing gas and used as a dental anesthetic, accounts for well under 10 per cent of greenhouse gas emissions.

But it’s almost 300 times as potent as carbon dioxide at trapping energy, the greenhouse effect believed to be warming the planet. It has long been known that agriculture is a prime source of nitrous oxide emissions, due largely to the nitrogen-based fertilizers used to produce food worldwide.

But largely overlooked was the impact of fields in northern climates that freeze during the winter and then thaw, said Wagner-Riddle, whose study was published in the journal Nature Geoscience. As the ground defrosts, microbial activity releases nitrous oxide into the environment.

The Guelph team set up devices on fields in Ontario and Manitoba that automatically analyzed the gases flowing upward, for 14 and nine years respectively, to account for yearly variations in conditions.

They then gathered readings from 10 other locations in Canada, as well as in the U.S., Japan, China and Germany, and extrapolated their findings to cropland worldwide that is subject to freezing and thawing.

Their conclusion: the unique process churns out a teragram — one billion kilograms — of nitrous oxide a year, a source never quantified before.

That would mean the contribution of agriculture to production of the gas has been underestimated by 17 to 28 per cent, says Wagner-Riddle’s study.

But wouldn’t global warming itself counteract the phenomenon, reducing the amount of farmland that freezes in winter? In fact, the opposite may be occurring, said the Guelph professor.

Climate change can reduce the amount of snow, which serves as an insulating layer on soil, meaning that ground might be more likely to freeze, not less.

Planting cover crops that remain in the earth over winter, as well as notill farming — where the ground is not churned up after harvest — have been shown to reduce nitrous oxide emissions, she said.

Bonnett said a majority of Canadian farmers have already embraced notill farming and some are using cover crops now. Both measures have benefits apart from helping the environment, he said.