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The Nation’s Corn Belt Has Lost a Third of Its Topsoil

Researchers used satellite imaging and surface soil color to find out how much of the nutrient-rich earth has eroded away Becca Dzombak

"Soil erosion issues are real and are affecting food production around the globe and in some locations are leading to massive migration. This article from tells us the story and

why we must care."

Jeannette Kravitz, Executive Director Campaign.

Seth Watkins has been farming his family’s land in southern Iowa for decades, growing pasture for his cows as well as corn and other row crops. His great-grandfather founded the farm in 1848. “He came in with one of John Deere’s steel plows and pierced the prairie,” Watkins recounted. With its rolling hills and neat lines of corn stretching to the horizon, broken by clumps of trees, it’s a picturesque scene.

But centuries of farming those hills have taken their toll on the soil. Now, farmers like Watkins are facing widespread soil degradation that can lower their crop yields and incomes. “In 150 years or so, we’ve lost over half of that rich topsoil—if not all in some places.”

Crops hunger for the carbon-packed composition of rich topsoil. They need the nutrients and water that it stores, unlike the compacted, infertile soils that decades of conventional farming create.

The baseline for soil in Iowa is visible on land owned by Jon Judson, a sustainable farmer and conservation advocate. His farm hosts a rare plot of original prairie grasses and wildflowers. Under the prairie, the soil is thick and dark, with feet of organic matter built up and plenty of moisture. The next field over is a recovering conventional field like Watkins’ farm, and the effect of years of conventional practices is obvious. The soil is pale and compacted, with only a few inches of organic carbon, much less soil moisture, and a lot more clay.

Scientists and farmers know that agricultural soil erosion has been a problem for decades, but quantifying soil loss from a hundred years of farming and across multiple states has proven difficult. Now a study led by geomorphologist Evan Thaler and published in Proceedings of the National Academy of Sciences in February attempts to answer the elusive question of how much topsoil has been eroded in the Corn Belt, which stretches roughly from Ohio to Nebraska and produces 75 percent of the nation’s corn. The study estimated that about 35 percent of the region has lost its topsoil completely, leaving carbon-poor lower soil layers to do the work of supporting crops. Having thick, healthy topsoil means plants can grow faster and healthier, increasing crop yields and keeping the field’s ecosystem running smoothly. Topsoil loss creates environmental problems, such as when eroded, nutrient-laden dirt degrades streams and rivers, and is estimated to cost the Midwest’s agricultural industry almost $3 billion annually.

“I think it’s probably an underestimate,” says Thaler, a graduate student at the University of Massachusetts–Amherst. “There are areas where there’s probably a centimeter of topsoil left.”

Thaler and colleagues used soil color from satellite imagery to track which areas of Corn Belt fields were lighter or darker. Darker soils have more organic carbon, which is a good indicator that the topsoil is present. Further down in soil, less organic carbon builds up, so once those layers are exposed, the surface looks lighter. Thaler then connected a color map he created to high-resolution topographic data, which told him where slopes were steep and whether hilltops were curved in or out. When he compared soil color to hills’ shapes, the map confirmed what he and countless farmers have noticed: the tops of hills are light, and their bases are dark. Plowing and precipitation lead rich topsoil to slowly creep downhill, leaving thin, carbon-poor soil uphill. Thaler found that highly curved hilltops are more likely to have eroded topsoil. That relationship drives his general finding of highly eroded soils in the Corn Belt, but it has been missing from erosion research until now.

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