Our planet provides numerous resources that are critical to human survival. While Earth’s dwindling water supplies rightly garner a lot of attention, the one directly below our feet is just as vital to life…and just as at risk of being used beyond capacity. Several studies in recent years have shined a light on our planet’s loss of topsoil, the uppermost layer of soil in which 95% of the world’s food is grown. New research shows this precious resource is eroding as much as 1,000 times faster than it forms in some parts of the US Midwest.
The latest data comes from the University of Massachusetts Amherst and made use of a rare element known as beryllium-10 to calculate natural erosion rates. Beryllium-10 occurs when stars in the Milky Way send high-energy particles, aka cosmic rays, toward Earth. When this energy hits the Earth’s crust, it splits oxygen in the soil apart, leaving tiny trace amounts of beryllium-10 behind.
The team collected deep soil core samples from fourteen small patches of remnant native prairie that still exist in Iowa, Minnesota, South Dakota, Nebraska, and Kansas. According to Isaac Larsen, professor of geosciences at UMass Amherst and the paper’s senior author, the material collected dates as far back as the last Ice Age, around 12,000 years ago.
“Our median pre-agricultural erosion rate across all the sites we sampled is 0.04 mm per year,” says Larsen. That natural erosion rate represents the soil’s equilibrium point, where soil accumulates as quickly as it wears away. Any increase in the pace above that number, the study says, suggests the soil is disappearing faster than it is building up.
For agriculture to be sustainable, soil erosion rates must be low enough to maintain fertile soil. That’s because when topsoil erodes, the nutrients crops need go with it, making it more difficult for soil to store water and support plant growth. According to Iowa State University agronomy professor Richard Cruse, farmers can lose 50% to 70% of their yield potential because of the loss of topsoil
Unfortunately, Larsen and his team say that topsoil in some parts of the Midwest are experiencing far greater erosion, disappearing at 1,000 times the natural rate. What’s more, Larsen points out that the USDA’s current limit for erosion is 1 mm per year—twenty-five times greater than the average rate his team came up with. Meaning the USDA’s own guidelines will inevitably lead to loss of topsoil.
The new report builds on research published earlier this year that showed 57.6 billion metric tons of Midwest topsoil has eroded over the last 160 years. In that study, Larsen and his team measured the elevation differences between native prairie and farm fields across Midwestern states to see how tilling has changed landscapes. On average, farmed fields were 1.2 feet below the prairie. 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.
“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.” (Sources: Phys.org, GeoScienceWorld, NPR)
