U study identifies key culprits in cropland greenhouse emissions

A University of Minnesota study released last week has pinpointed two large contributors of global cropland greenhouse gas emissions.

by Ryan Faircloth

Certain agricultural practices play an outsized role in greenhouse gas emissions, according to University of Minnesota researchers.

The new University study, published on Nov. 21, has identified key contributors to agricultural greenhouse gas emissions — specifically, peatland drainage and rice paddy cultivation account for roughly 80 percent of the world’s total cropland emissions.

Paul West, a study researcher and co-director of the University’s Global Landscapes Initiative, said when peatlands are drained, usually for agriculture, the materials in the soil — such as leaves, sticks and other organic matter — decay and are converted to carbon dioxide.

And there’s no climate-friendly way to manage peatlands, he said, since they emit “tremendous” amounts of carbon regardless of how they’re maintained.

Rice paddies, however, have more management options, West said.

Since paddy rice is managed by flooding the fields, soil materials don’t receive oxygen and are broken down — releasing methane, he said. This greenhouse gas is 34 times more powerful than carbon dioxide, but doesn’t last as long in climate, he said.

With croplands contributing roughly 5 percent of the world’s greenhouse gases, discovering ways to mitigate their emissions is an important step toward combating climate change, said Nathan Mueller, a postdoctoral research fellow at Harvard University and a study author, in an email.

Stopping peatland draining altogether is the best way to combat its emissions, said James Gerber, a study author and co-director of the Global Landscapes Initiative.

“Drainage just has to stop, and policies need to be implemented to help encourage farmers to stop doing that,” he said.

Still, the only way policies would be executed is if they don’t harm the agriculture industry, Gerber said.

“Ideally, you would develop policies that would reward farmers for good behavior, not punish them for bad behavior,” he said.

And peatlands should be discouraged anyway, since there are other areas for crop production that pose less environmental harm, Mueller said in an email.

In rice fields, drying when not actively growing crops could help reduce emissions, West said, adding that studies have shown it won’t negatively impact rice production.

But this isn’t an easy fix either, West said, because there has to be a farming system in place that would release the water that’s not being used.

Other emitters considered problematic in the study include nitrogen fertilizers, which are used to sustain crop yields and soil health. When more fertilizer is used, emissions of nitrous oxide — which is 298 times more powerful than carbon dioxide — increase.

Because this was the first study to identify crop-specific emission sources, Gerber said he hopes the research will aid in future intervention efforts.

“The global result isn’t new. The specificity is … very novel,” he said. “We really hope we’ll be able to help target policy to design intervention.”