Metric loss

The Midwest has lost 57 billion metric tons of topsoil over the past 160 years, new study finds

A few years ago, Isaac Larsen attended a wedding at a pioneer church in Minnesota. After the ceremony, he strolled through a cemetery near the church.

He noticed that the cemetery, which had never been plowed, was at least a foot higher than a cornfield just beyond a fence.

“It was one of those ‘lightbulb’ moments that told me that a lot of soil had been eroded from this field since the church was founded,” Larsen said.

Geosciences professor Amherst from the University of Massachusetts and his co-researchers published a new study that the topsoil found in the Midwest is eroding at an average rate of 1.9 millimeters per year. They measured elevation differences between native grasslands and agricultural fields at about 20 sites, the majority in central Iowa, with some in Illinois, Minnesota, South Dakota, Kansas and North America. Nebraska.

Researchers estimate that the Midwest has lost 57.6 billion metric tons of topsoil since farmers began plowing 160 years ago. This erosion, Larsen said, makes it harder and more expensive to grow crops.

“We’re going to have to feed more people in the future,” he said, “and degraded soils that have lost their rich organic horizons just aren’t as productive.”

The solution, Larsen said, is to embrace no-till agriculture. “It’s not an insoluble problem.”

In Iowa, prairie ever cultivated is one of the rarest ecosystems besides oak savannah, said Emily Martin, conservation programs coordinator for the Iowa Natural Heritage Foundation. The group helped researchers identify grassland sites across the state where they could take action.

Martin said the study’s findings of topsoil eroding at an average rate of 1.9 millimeters per year are “a shocking number. But that’s not surprising either. She said conservation groups like the Iowa Natural Heritage Foundation need to work with farmers to protect the land and integrate conservation more into farming.

As topsoil thins, soil productivity decreases. Iowa State University agronomy professor Richard Cruse said farmers can lose 50 to 70 percent of their yield potential due to topsoil loss.

“When you talk about that, you’re also talking about sustainability or resilience, the potential for a region to produce in good times and bad,” Cruse said. “Loss of soil reduces this ability.”

Cruse, who said he thought the study was “pretty well done”, added that the topsoil has not disappeared. Most of the topsoil that shifts due to erosion is deposited in the same field downstream. But it still affects production potential, he said.

“The loss of the slope, where it gradually thins, has a much greater negative impact on production than the accumulation of that on the ground downstream which already has more than adequate topsoil to produce,” said he declared.

Cruse added that just under a third of Iowa’s soil is untilled, so “it’s realistic” to stop tillage, he said.

“Overall, we now have the technology to do no-till or something like that, maybe down to strip,” Cruse said. “So it’s realistic. It is more difficult with some soils than with others.

Some farmers already practice no-tillage. The US Department of Agriculture said in August 2021 that 21% of all cultivated cropland acres are no continuous tillage.

Austin Charlson grows corn and soybeans in Wright County, Iowa. About 75-85% of his acres have been zero-till for the past seven years, mostly because he had no equipment when he started farming. He says he noticed a difference in the soil on his no-till acres.

“I’ll get a spade out in the field and step in, dig up a section of soil and the texture evolves,” Charlson said. “On the one hand, there are more worm holes, which promote the descent of water and oxygen to the roots. Earthworms add fertility and help break up the soil.

Charlson said his soils are “more crumbly” whereas other soils he’s seen on a field that’s been plowed and cultivated are more gritty, “really fine as powder,” he said. .

“At the moment, we are in drought conditions, but direct seeding helps me to reserve my water reserves. It helps retain the moisture in my basement or the water my crops need to grow,” he said.

But Charlson said he had experienced some frustrations with no-till. Depending on moisture conditions, the soil can be hard without tillage, which doesn’t make for a good seedbed, he said.

“It was a challenge,” he said. “I’m constantly learning, trying to change things and improve.”

The soil erosion study was published in the journal The Future of Earth.

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Harvest Public Media reports on food systems, agriculture, and rural issues through a collaborative network of NPR stations throughout the Midwest and Plains.