More Than 50 Billion Tons of Topsoil Have Eroded in the Midwest

Since farmers began tilling the land in the Midwest 160 years ago, 57.6 billion metric tons of topsoil have eroded, according to a study published recently in Earth's Future.  The loss has occurred despite conservation efforts implemented in the 1930s after the Dust Bowl, and the erosion rate is estimated to be double what the U.S. Department of Agriculture (USDA) says is sustainable. Future crop production could be severely limited if it continues, reports Rachel Crowell for Science News.

Degraded soil makes growing food more difficult and expensive. Without healthy soil, farmers won't be able to grow nutrient-dense food to feed our growing population. The calculated loss in the region is part of a critical issue; some experts suspect that Earth will run out of usable topsoil within 60 years.

The team of researchers led by geoscientists at the University Massachusetts Amherst measured the elevation differences between native prairie and farm fields across Midwestern states to see how tilling has changed landscapes. Native prairie remnants are higher than the surrounding land, the study explains.

The majority of the 20 investigated sites were located in central Iowa, but other places were studied in Illinois, South Dakota, Minnesota, Kansas and Nebraska, reports Katie Pikes for Harvest Public Media. "These rare prairie remnants that are scattered across the Midwest are sort of a preservation of the pre-European-American settlement land surface," says Isaac Larsen, study author from the University of Massachusetts Amherst, to Science News.

The research team had help from the Iowa Natural Heritage Foundation to identify sites for the study. On average, farmed fields were 1.2 feet below the prairie, per Science News. After measuring soil height in each area, the team found that, on average, topsoil is eroding at a rate of 1.9 millimeters per year, Harvest Public Media reports.

When topsoil erodes, the nutrients crops need go with it, making it more difficult for soil to store water and support plant growth. Farmers can lose 50 to 70 percent of their yield potential because of the loss of topsoil, reports Harvest Public Media. Rapid erosion is a problem because recovering topsoil is a slow process that takes years. Generating just over an inch of topsoil takes 1,000 years, said Maria-Helena Semedo of the United Nation's Food and Agriculture Organization in 2014. 

Topsoil can erode due to strong winds, hard rains and flowing water. Farming practices like tilling, the process farmers use to overturn the ground to prepare it for crops, leave the soil vulnerable to surface runoff. One way to help mitigate the loss of topsoil is to have farmers use no-till practices to grow crops. "By and large, we have the technology now to make no-till work or something that approximates it, maybe strip till," Richard Cruse, an agronomy expert at Iowa State University not involved with the study, says to Harvest Public Media. "So, it's realistic. It's more challenging with some soils than others."

According to the USDA, no-till practices have already been implemented by 51 percent of soybean, cotton, corn and wheat farmers in the U.S. Cover crops may also be a solution—they are plants grown during the offseason—but are only used in about 5 percent of cases, Bruno Basso, an agricultural researcher at Michigan State University not involved with the study, says to Science News. 

"As erosion degrades our soils, it reduces our ability to grow food," Larsen explains in a press release. "Combine this with increasing global population and climate stress, and we have a real problem."

Elizabeth Gamillo | | READ MORE

Elizabeth Gamillo is a correspondent for Smithsonian and a science journalist based in Milwaukee, Wisconsin. She has written for Science magazine as their 2018 AAAS Diverse Voices in Science Journalism Intern.