A climate conundrum beneath our feet: Minnesota's farmed peat soil releases greenhouse gases

Researchers have identified a key source of greenhouse gases in Minnesota, and now they have to figure out where it is — and what to do about it.

The culprit? The state's soggy, carbon-packed peat soil, drained and farmed in places for decades.

Mapping the disturbed soils, ascertaining their uses and quantifying their greenhouse gas emissions is key to the state's struggle for climate solutions that don't turn Minnesota's farm economy on its head.

"The emissions from agriculture overall are sort of surprising," said Anne Claflin, the research scientist at the Minnesota Pollution Control Agency (MPCA) who heads the state's greenhouse gas inventory. "We think about emissions from fossil fuel. The other systems that are part of our daily life and our state economy, that aren't in that fossil fuel carbon cycle, sort of fly under the radar."

Although true peat bogs are concentrated in Minnesota's north, the state has an estimated 6 million acres of rich peat soils scattered around, more than any other state except for Alaska. Only Michigan, Wisconsin and Florida come close.

The MPCA estimates about 800,000 acres have been drained for crops or pasture, although new research from the Nature Conservancy puts the total closer to 330,000. Either way, the disturbed peat soil emits a lot of greenhouse gases. The MPCA puts the greenhouse gas emissions from such "cultivated histosols" at a whopping 11 million metric tons a year.

That puts disturbed peatlands as the state's fourth-highest source of emissions, just behind natural gas, coal and "light duty trucks," which includes small and mid-sized pickups. Even at half that amount, the gassy soils pose a major climate challenge for agriculture, right up there with emissions from cow burps, manure and fertilizer.

Researchers are stretching for solutions. The one favored by conservation groups and some state officials is the most direct — and farmers have heard it before: remove the land from production and restore the natural wetlands. Protecting and restoring peatlands and other wetlands is a point in Minnesota's draft climate action framework released Feb. 1.

Other ideas to lower the peat soil emissions include reduced tilling, fine-tuning fertilizer application, adding cover crops and switching to lower-impact crops such as wild rice, cranberries or mint.

"What we're all thinking about is where is the low-hanging fruit we can go after for mitigation purposes," said University of Minnesota soil scientist Timothy Griffis. "From an efficiency standpoint you could ask, 'How much food is produced relative to how much greenhouse gas is lost?' That's one way to look at it."

The state's official greenhouse gas inventory classifies the farmed peatlands as cultivated histosols. It's a broad group of wet, peaty soils with a thick top layer of dense organic matter, mostly from rotting plants, that runs at least 16 inches deep. Think bogs, fens, mires and muck.

"We just happen to be blessed with a lot of them," said the MPCA's Climate Director Frank Kohlasch.

Cultivation changes equation

Minnesota's peatlands formed as the glaciers that flattened the state retreated some 10,000 years ago, leaving cold, wet conditions for plants sprouting in the muck left behind. The dead plants and animals just kept stacking up, said U soil scientist Nic Jelinski.

Left alone, the water-logged soil lacks oxygen and traps enormous amounts of carbon, although anerobic microbes emit methane.

That all changes with draining and plowing. Oxygen enters and more vigorous oxygen-loving microbes multiply. They feast on the vast stores of carbon, spewing greenhouse gases in a decades-long process.

"Some of these peatlands can be 30, 35 feet deep and it's just all carbon and carbon products," said Randy Kolka, research soil scientist with the U.S. Forest Service in Grand Rapids. "When you start disturbing these ecosystems for any reason, they are prime to flip from being sinks of carbon to being sources."

A lands team that's part of Gov. Tim Walz's climate change subcabinet is cataloging the drained peatlands and their gases.

Kristen Blann, a freshwater ecologist with the Nature Conservancy in the Upper Midwest and a member of the team working to map the acres, said most of the farmed peat soils appear to be covered with corn, soybeans, hay, alfalfa and other crops. Cultivated wild rice and sod are also grown on these soils. Pasture covers the remaining 88,000 acres, according to her research.

Companies in Minnesota also mine peat and sphagnum peat moss directly for the horticulture industry — even for flavoring a local whiskey. Large combine-looking vacuums are sometimes used to hoover up the soil and moss. Peat harvesting in Minnesota emits an additional 124,000 tons of greenhouse gases a year, according to the state inventory.

But many more acres are planted with row crops. Blann's research shows a pocket of heavy peatland cultivation in central Minnesota, for example. Stearns, McLeod and Meeker counties rank at the top for farmed acres, much of it in corn and soybeans.

Blann said the goal is to eventually create an interactive soils map people can use to help with conservation planning.

The idea is that established conservation programs — such as easements and wetland banking — could be adapted to target peatlands and create incentives for farmers to set them aside.

Restoration challenge

Restoring peat ecosystems is the best way to address the problem, said Kolka, with the U.S. Forest Service: "Plugging the ditches, bringing the water tables back up and planting the native vegetation to the best of our ability. That's our best bet."

It's a formidable challenge.

Farmers know their fields well and where they have more organic material, but they won't likely know if that's a histosol, said Larry Lahr, who farms in Stearns County near Cold Spring. Lahr suspects that a fat buffer on his land near a creek might be peatland, but he doesn't think it's ever been tilled.

Lahr and his wife, Jennifer, are part of a pilot project studying now much carbon is released from their farming practices and how practices such as cover cropping might reduce emissions. But the project doesn't target peat soils that he's aware of, he said.

Farmers won't rush to permanently idle land, Lahr said, particularly if it's rich soil.

"It's the most productive acres that we have," he said.

Restoring any kind of wetland, including soggy peat soil, is expensive.

"That's the sad truth. Nobody can afford it," said Dennis Rodacker, wetland mitigation supervisor at the Minnesota Board of Water and Soil Resources. "Everything's a great idea until someone has to pay for it, and then the wheels fall off."

Some question whether efforts should focus instead on conserving the peat that remains.

A prime candidate, Blann said, is the 500,000 acres of peatlands in northern Minnesota that were ditched long ago but were abandoned when the ground proved too difficult to farm. These acres are not included in the Nature Conservancy's estimate that 330,000 acres of peat soils are farmed.

"We are working on a strategy," said Nature Conservancy spokesman Chris Anderson. "It's the best bang-for-your-buck climate strategy that we've got."