One-Third of Farmland in the U.S. Corn Belt Has Lost Its Topsoil

Soil erosion in corn field in Nebraska.

Soil erosion in corn field in Nebraska. Photo: University of Nebraska-Lincoln

More than a third of farmland in the U.S. Corn Belt — nearly 100 million acres — has completely lost its carbon-rich topsoil due to erosion, according to a new study published in the journal Proceedings of the National Academy of Sciences. The loss of topsoil has reduced corn and soybean yields in the Midwest by 6 percent, resulting in a loss of nearly $3 billion a year for farmers, and increased runoff of sediment and nutrients into nearby waterways, worsening water quality.

The study, led by scientists at the University of Massachusetts, Amherst, found that the greatest loss of carbon-rich topsoil was on hilltops and ridgelines — indicating that tillage, or the repeated plowing of fields, was largely to blame as loosened soils moved downslope. The research also found that this erosion has removed nearly 1.5 petagrams of carbon from hills in the Corn Belt. Restoring the topsoil, the study’s authors argued, could help productivity and potentially turn agricultural fields into carbon sinks.

Previous research has shown that no-till farming practices can have a significant impact on reducing erosion. A study published last November in the Journal of Environmental Management found that if farmers shifted entirely to no-till practices, it would reduce soil erosion from U.S. agricultural fields by more than 70 percent, helping to significantly reduce nutrient and sediment runoff and improve water quality along thousands of miles of streams and rivers.

Even partial changes in tilling practices could produce positive results for waterways, according to the research. “If we focus on the most vulnerable area in terms of soil erosion, then only 40 percent no-till shows almost the same reduction as 100 percent no-till implementation,” Sanghyun Lee, a doctoral student at the University of Illinois and lead author on the tillage study, said in a statement.

Despite this growing evidence, no-till agriculture still makes up just a small portion of U.S. farming. Less than 15 percent of farmland in the upper Mississippi River watershed, the heart of the Corn Belt, is farmed with no-till practices. Nationwide, in watersheds from the Colorado to the Delaware rivers, just 21 percent of corn, soybean, cotton, and wheat fields are continuously farmed with no- or strip-till practices.

Scientists warn that unless farming methods change, U.S. soils will continue to become denuded. And as crop yields decline, farmers will have to increase fertilizer use, further worsening water quality for streams and rivers.