Extending US Breadbasket Fertility for Centuries: Strategies for Preserving Our Soil

The US Midwest has lost 57.6 billion tons of topsoil due to agricultural practices over the past 160 years, and the erosion rate, even following USDA guidelines, is still 25 times higher than the rate of topsoil formation.

However, there is no need to despair: researchers from the University of Massachusetts Amherst recently reported in the journal Earth’s future that no-till farming, which is currently practiced on 40% of crop acres in the Midwest, could expand the current level of soil fertility over the next several centuries. This has implications for everything from food security to climate change mitigation.

The vast majority of the food we all eat is grown in topsoil, that carbon-rich black earth that nourishes everything from watermelons to Brussels sprouts. What most of us call topsoil, scientists call horizon A soil, and horizon A soil, whose fertility has evolved over eons, is subject to erosion.

says Jeffrey Quang, a postdoctoral fellow at the University of Minnesota who completed this research as part of postdoctoral studies in the Isaac Larsen Geomorphology Research Group at UMass Amherst and is lead author of the paper. “It turns out that the biggest driver of soil erosion in the Midwestern United States was traditional farming.”

But it has been very difficult to accurately determine the current rate of erosion, although, as the Geomorphology Research Group has shown over the past few years, soil erosion in the US breadbasket is much greater, and occurring at a much faster rate, than previously suspected.

A Brief History of Soil Loss in the Midwest

Since 2021, members of Larsen’s research group, including Kuang, Evan Thaler, Caroline Quarrier, and others, have begun to break new ground in the world of soil science.

The group’s initial study showed that more than a third of the Midwest’s corn belt—nearly 30 million acres—has completely lost its carbon-rich topsoil, that layer rich in A horizon. Furthermore, the team showed that erosion was likely due to contemporary tillage practices, as plows were dragged across the fields, moving the topsoil from higher to lower elevations. Unfortunately, the USDA’s own assessments do not include erosion due to tillage, so the agency missed a major driver of erosion.

A year later, the team discovered that the Midwest had lost 57.6 billion metric tons of soil since Euro-American agriculture began in the region, some 160 years ago. This historical rate of loss, which is mostly due to tillage, is nearly twice the rate that the USDA considers sustainable.

Finally, the team recently showed that Midwestern soils are eroding between 10 and 1,000 times faster than they were in the pre-agricultural era, and that the current USDA upper limit for sustainable erosion — 1 mm per year — is on average 25 times more which is already sustainable.

Modeling the future

“We’ve already explored how the history of erosion in the United States has shaped our current reality,” says Isaac Larsen, associate professor of earth sciences, geography and climate at UMass Amherst and lead author of the paper. “But what will happen in the future?”

In this latest paper, Kuang, Larsen, and the Geomorphology Research Group relied on insights from their previous work on historical rates of erosion to predict future scenarios. Their first discovery was to determine the current rate of soil erosion caused by tillage. It turns out that the Midwest loses 1.1 kilograms of soil and 12 grams of soil organic carbon per square meter each year, which far exceeds the rate at which new topsoil is formed.

But no one knows what the future will look like. “Since we don’t know how agricultural practices and policies will change, we used the current rate of erosion to model a few different future scenarios,” says Larsen.

“We looked at the current business as usual, under which approximately 40% of acres in the Midwestern United States are farmed no-till, up to 100% no-till. We then modeled erosion rates under each scenario for the next century.” says Kwang.

Their preliminary finding was that if current US farming practices remain largely unchanged, approximately 8.8 billion metric tons of soil and 170 million metric tons of soil organic carbon will be lost over the next century alone.

When the team modeled the effect of the 100% no-till scenario, the picture became much rosier. more rosy.

“Nearly 95% of the erosion we see under a business-as-usual scenario will be prevented over the next century,” says Kwang.

In other words, the soil savings are so great that if the US adopted no-till practices now, it would take 10,000 years to see the same level of soil and SOC loss that would occur in just a century if our agricultural practices did not change.

Moreover, the rate of loss decreases over time: the more soils and SOC, the faster we lose them, and loss rates decrease because there is less loss. “It means there is a real incentive to act now, when we see the greatest long-term benefit,” says Kwang.

soil and climate

Not surprisingly, topsoil is important to farming; But most greenhouse gas emissions projections and climate mitigation plans also need to account for topsoil loss, because soil is the largest pool of terrestrial carbon. Scientists hypothesize that accelerated soil erosion changes this carbon pool enough to affect the global carbon cycle.

However, Quang says, “Most models that look at soils and their impacts on climate do not account for slowing rates of erosion over time. We need to get this right if we want to prepare effectively for the future — and we know we have a rate that can help forecast predictions of what might happen.” That will be the climate of the future.”