Ensuring the Longevity of U.S. Breadbasket Fertility: Preserving Our Soil for Future Generations

Caption: UMass Amherst geosciences professor Isaac Larsen observing the erosional escarpment at Stinson Prairie, Iowa. (Credit: UMass Amherst)

A recent study conducted by UMass Amherst reveals that the alarming rate of topsoil erosion can be significantly reduced by implementing sustainable agricultural practices, specifically the use of no-till farming.

Over the past 160 years, farming practices have resulted in the loss of a staggering 57.6 billion tons of topsoil in the Midwestern United States. Even when following the guidelines set by the U.S. Department of Agriculture, the erosion rate remains 25 times higher than the natural formation rate of topsoil. However, there is hope: researchers from the University of Massachusetts Amherst have published a paper in the journal Earth’s Future, indicating that the adoption of no-till farming, currently implemented on 40 percent of cropland acres in the Midwest, can preserve soil fertility for several centuries to come. This has significant implications for food security and mitigating climate change.

Topsoil, also known as A-horizon soil among scientists, is the vital medium in which we grow the majority of our food. This carbon-rich, black earth nurtures a wide variety of crops, from watermelons to brussels sprouts. Unfortunately, A-horizon soils, which have taken centuries to develop their fertility, are highly vulnerable to erosion.

“Many people associate erosion with wind or water, but conventional agriculture has been the primary driver of soil erosion in the midwestern U.S.,” explains Jeffrey Kwang, lead author of the paper and former postdoctoral fellow at the University of Minnesota who conducted the research as part of Isaac Larsen’s Geomorphology Research Group at UMass Amherst.

Quantifying the exact rate of erosion has proven challenging, but the Geomorphology Research Group has made groundbreaking discoveries over the past few years, revealing that soil erosion in the Midwest’s agricultural heartland is more severe and faster than previously believed.

A Historical Overview of Soil Loss in the Midwest

Since 2021, Larsen’s research group, comprising individuals like Kwang, Evan Thaler, Caroline Quarrier, and others, has been at the forefront of soil science.

Their initial study disclosed that approximately one-third of the Midwest’s Corn Belt, amounting to nearly 30 million acres, has completely lost its carbon-rich topsoil, the vital A-horizon layer. Furthermore, the team established that contemporary tillage practices, involving the use of plows to move topsoil from higher to lower elevations, were the likely cause of this erosion. Regrettably, the USDA’s assessments did not account for tillage-induced erosion, leading to a significant oversight in identifying a major contributor to soil loss.

One year later, the team uncovered the astonishing fact that the Midwest has lost a staggering 57.6 billion metric tons of soil over the past 160 years since Euro-American cultivation began in the region. This historical erosion rate, primarily driven by tillage, is nearly double the sustainable rate recognized by the USDA.

Lastly, the team’s recent research demonstrated that soil erosion in the Midwest is occurring at a rate 10 to 1,000 times faster than in the pre-agricultural era. The USDA’s current upper limit for sustainable erosion, set at 1 mm per year, is on average 25 times higher than what is genuinely sustainable.

Predicting the Future

Isaac Larsen, senior author of the paper and associate professor of earth, geographic, and climate sciences at UMass Amherst, emphasizes the importance of understanding the future implications: “We have already examined how the history of erosion in the U.S. has shaped our present reality, but what lies ahead?”

To answer this question, Kwang, Larsen, and the Geomorphology Research Group relied on their earlier insights into historical erosion rates to develop future scenarios. They initially determined the current rate of tillage-induced soil erosion, revealing that the Midwest loses 1.1 kilograms of soil and 12 grams of soil organic carbon (SOC) per square meter annually, surpassing the rate at which new topsoil is formed.

However, the future remains uncertain, as Larsen explains, “Since we cannot predict farming practices and policy changes, we based our models on the current erosion rate and explored various future scenarios.”

“We examined both the business-as-usual approach, with approximately 40% of Midwest acres using no-till farming, and a scenario with 100% adoption of no-till methods. Subsequently, we projected erosional rates under each scenario for the next century,” adds Kwang.

Their findings revealed that if current agricultural practices remain unchanged, approximately 8.8 billion metric tons of soil and 170 million metric tons of soil organic carbon will be lost in the next century alone.

However, when the team modeled a 100% adoption of no-till practices, the results were significantly more optimistic—nearly 95% of the erosion projected in the business-as-usual scenario for the next century could be prevented.

To put it simply, the potential soil conservation achieved through widespread implementation of no-till practices is remarkable. If the United States adopts no-till farming now, it would take 10,000 years to witness the same level of soil and SOC loss that could occur in just a century if our agricultural practices remain unaltered.

Moreover, the rate of loss decreases over time, as the available soil and SOC diminish. This provides a compelling incentive to take immediate action, as the most significant long-term benefits can be realized by acting promptly.

Soil Preservation and Climate Considerations

The crucial role of topsoil in agriculture is well-known, but it is equally important to consider topsoil loss when predicting greenhouse gas emissions and formulating climate mitigation strategies. This is because soil represents the largest terrestrial carbon reservoir, and accelerated soil erosion can significantly impact the global carbon cycle. However, existing models examining the relationship between soil and climate often overlook the reduction in erosion rates over time. It is essential to account for this aspect to make accurate predictions for future climate conditions and plan effectively.

Kwang emphasizes, “If we are to prepare adequately for the future and develop reliable climate predictions, we need to ensure that models accounting for soil and its impact on climate incorporate erosion rates decelerating over time.”

Reference: “The Future of Soils in the Midwestern United States” by J. S. Kwang, E. A. Thaler and I. J. Larsen, 25 May 2023, Earth’s Future.
DOI: 10.1029/2022EF003104

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• UMass Amherst: Link to UMass Amherst website
• Earth’s Future: Link to the paper on Earth’s Future journal