America’s corn belt has lost a third of its topsoil

By | April 15, 2021

Becca Dzombak reports:

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. [Continue reading…]

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