According to a new study published in the journal Earth’s Future from the University of Massachusetts Amherst, agricultural fields in the Midwestern United States have lost an average of two millimeters of soil per year since Euro-American colonization about 160 years ago. .
Soil erosion rate doubled
The USDA considers this to be nearly double the rate of erosion considered sustainable. Additionally, USDA erosion estimates are three to eight times lower than the numbers reported in the study. Finally, the study authors conclude that plowing, rather than wind and water, is the root cause.
“My wife and I were at a wedding at a Norwegian pioneer church in Minnesota a few years ago,” says Isaac Larsen, professor of geosciences at UMass Amherst and one of the paper’s co-authors. “After the ceremony, I walked to the edge of the cemetery, which was surrounded by cornfields, and was amazed to find that the surface of the field was a few feet lower than the surface of the ever plowed cemetery. . I started to wonder why.”
After a few years, Larsen, along with the paper’s co-lead authors, Evan Thaler, who completed the research as part of his Ph.D. at UMass Amherst, and Jeffery Kwang, a postdoctoral fellow at UMass Amherst at the time of the study, found himself in central Iowa on the “escarpment,” or drop, separating a native prairie from a field of soy.
Thaler had spent a lot of time working with the Iowa Natural Heritage Foundation and other organizations to identify the few remaining pockets of original, never-cultivated prairie. He then approached the farmers whose lands bordered the prairies, asking permission to survey their fields.
Thaler ended up with twenty sites, the vast majority of which were in central Iowa, with a few in Illinois, Minnesota, South Dakota, Kansas, and Nebraska. “I drove around the Midwest for days knocking on doors,” Thaler explained. “Before they allow you into their property, people want to see your face and have a conversation with you. When I arrived in person, no one turned me away.”
The team got to work as soon as Thaler got permission from the landowner. The team walked dozens of transects or perpendicular routes across the escarpment, from untouched grassland to eroded agricultural field, stopping every few centimeters to measure elevation change with an extremely sensitive GPS device that looks more like a floor lamp than a handheld. device. They repeated this hundreds of times over the summers of 2017, 2018 and 2019.
The team used historical land use records and state-of-the-art computer models to reconstruct erosion rates in the Midwest once they had their raw data. They found that topsoil in the Midwest is eroding at a rate of 1.9 millimeters per year on average.
In other words, the authors estimate that the Midwest has lost about 57.6 trillion metric tons of topsoil since farmers began tilling the soil 160 years ago. This is despite conservation practices being implemented following the Dust Bowl in the 1930s.
It is also evident that much erosion is caused by tillage or plowing. “My modeling shows that plowing has a ‘diffusive’ effect”, Kwang said. “It melts the landscape, flattening the highest points of a field and filling in the hollows.” According to Thaler, the USDA has “significantly underestimated the rate of erosion” currently at work in the heartland because it does not explicitly include such “tillage erosion” in its own analysis. .
“As our soils deteriorate, our ability to grow food also deteriorates,” said Larsen. “When you combine that with the increase in world population and climate stress, we have a serious problem.” The researchers believe that more sustainable practices, such as no-till agriculture and soil regeneration, will be needed to “reduce rates of soil erosion in the Midwest to levels capable of maintaining soil productivity, services ecosystems and long-term prosperity”.
(Source: University of Massachusetts Amherst)