USDA-Funded Soil Scientist Probes Hidden Carbon Reservoirs Threatened by Climate Extremes

Beneath every harvest in the United States lies an intricate microscopic economy, one that most consumers never see but every farmer depends upon. Andi Jilling, an assistant professor of environmental health sciences at the University of South Carolina’s Arnold School of Public Health, has dedicated her research career to understanding that hidden world. Now, with the backing of the U.S. Department of Agriculture, she is leading two federally funded projects and serving as co-investigator on two more, all aimed at identifying the forces that degrade healthy soil and at protecting the productive land that feeds farms and dinner tables across the country. Her work arrives at a moment when the pressures on American agriculture have rarely been more complex, and when the scientific community is fundamentally revising its understanding of what keeps soil fertile.

The challenges confronting today’s farmers form an interconnected web that resists simple solutions. Rising production and distribution costs, chronic labor shortages, shifting trade agreements and policy regulations, evolving pest pressures, a changing climate, and increasingly uncertain water availability each place their own strain on agricultural operations. Together, these factors compound a quieter but equally consequential problem: the steady depletion of microscopic nutrients in the soil itself. As these pressures intensify, the farmers who must navigate them are becoming fewer and more isolated. According to USDA figures, the number of farms in the United States has fallen by roughly 72 percent from its peak of 6.8 million in 1935 to 1.88 million in 2024. Over the same span, direct employment on farms has collapsed from 25 percent of the national population to just one to two percent, leaving a shrinking workforce to shoulder an expanding set of trials.

Jilling’s expertise lies in how nutrients move through soil systems, a specialization that positions her at the center of one of agriculture’s most consequential scientific debates. Her USDA-funded projects are designed to understand how soils can be managed to support healthy, climate-resilient and productive ecosystems. The stakes are considerable: soil is not merely the physical substrate in which crops grow but a living reservoir of carbon, nitrogen and countless other elements whose availability determines whether a season ends in abundance or shortfall. Managing that reservoir intelligently, she argues, requires knowing far more about its internal architecture than science has historically possessed.

One of her two lead projects examines how climate change, expressed through erratic rainfall, intense storms and increasing drought, affects the storage of soil carbon and the availability of nitrogen for future crops. For generations, farmers and soil scientists have counted on soil organic matter as a key reservoir of plant nutrients, a bank of fertility that pays out steadily even in heavily fertilized systems. The central challenge, as Jilling frames it, is to measure and manage soil organic matter so that nutrients are released in the right ways and at the right times to benefit growing plants. That task has grown more urgent as weather patterns grow less predictable, because the mechanisms that lock nutrients away or set them free are far more sensitive to moisture than researchers once believed.

A closer look at soil’s composition reveals why. Soil organic matter comes in two fundamentally different forms. The first consists of partially broken-down plant matter that cycles quickly, responds sensitively to farming methods, and serves as an active, fast-moving supplier of nutrients. The second type, which constitutes the majority of soil organic matter, is tightly bound to minerals such as clay. Once these mineral-bound particles form, they can persist for decades or even centuries, and they have therefore long been regarded as stable, slow to change, and largely indifferent to farm management practices such as tillage or to external environmental forces. That assumption of permanence has shaped decades of soil science, agronomic advice and federal measurement standards.

Jilling’s work has upended that assumption. Her research has discovered that certain moisture conditions can unlock these mineral-bound reservoirs prematurely, releasing stored nutrients into the environment before plants have any opportunity to use them. To understand the scope of this vulnerability, she and her team are gathering samples of different soil types from Oklahoma, Virginia, South Carolina and Arkansas and running controlled laboratory experiments that expose the samples to moisture regimes mimicking the unprecedented wet-dry fluctuations that climate change is expected to bring. The experiments are designed to reveal precisely when and how mineral-bound organic matter destabilizes, and which soil types face the greatest risk of losing their long-term fertility stores.

Projected shifts in climate change suggest increases in droughts and a general intensification of wet-dry cycling, Jilling notes. Our goal is to help identify which agricultural soils are most vulnerable as the climate shifts. That identification task is far from academic. If scientists can pinpoint which soils are prone to premature nutrient release under alternating drought and deluge, farmers and policymakers can prioritize those lands for amended management practices, adjusted crop rotations or targeted conservation investments before irreversible losses occur. The research also carries implications for carbon accounting, since mineral-bound organic matter represents one of the largest long-term stores of carbon in agricultural landscapes, and its destabilization would mean that carbon, like nitrogen, could escape into the atmosphere or waterways.

The second project translates these fundamental insights into a practical policy test. The Jilling Lab is collecting data that could help the USDA’s Natural Resources Conservation Service decide whether to begin tracking mineral-bound organic matter as an official measure of soil health. Currently, the agency’s dynamic soil properties include partially broken-down plant matter but exclude its mineral-bound counterpart, reflecting the older view that the mineral-bound fraction changes too slowly to matter for management decisions. Jilling’s findings challenge that logic directly. If mineral-bound organic matter can become unstable and lose both carbon and nitrogen under certain conditions, then it may be just as dynamic, and just as informative, as the rapidly cycling fraction that regulators already monitor.

To build the evidence base for that decision, her team is collecting soil samples from annual and perennial cropland across the deliberately contrasting regions of South Carolina, from the clay-rich Piedmont to the sandy Coastal Plain. By comparing mineral-bound organic matter behavior across these divergent soil types and cropping systems, the researchers aim to assess whether the mineral-bound fraction deserves a place on the USDA’s official list of soil health indicators. A positive finding could ultimately reshape how soil health is measured and reported on farms nationwide, giving producers a more complete diagnostic picture of the fertility they are managing and giving federal agencies a sharper tool for targeting conservation programs.

Underlying both projects is a broader scientific evolution that Jilling describes with evident enthusiasm. Our understanding of soil has evolved to include a growing appreciation of factors such as the reactivity of mineral surfaces and microbe-mineral interactions, making mineral-bound organic matter much more susceptible to disruption than previously thought, she says. Previous research has shown that mineral-bound organic matter can be impacted by some types of land use and external elements, and we hope to add to that knowledge base by studying both the role of moisture in forming mineral-bound reservoirs and, across both projects, how plant-microbe-mineral interactions can destabilize them. In that three-way interplay of roots, microbes and minerals, Jilling and her collaborators are mapping the fault lines along which America’s agricultural foundation may shift, and providing the knowledge needed to reinforce it before the next drought, storm or shifting season arrives.

Subject of Research: USDA-funded research on how climate-driven moisture fluctuations destabilize mineral-bound soil organic matter and affect soil health measurement

Article Title: Andi Jilling leads USDA-funded projects to protect America’s soil health

Article References: Andi Jilling leads USDA-funded projects to protect America’s soil health. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: soil health, soil organic matter, mineral-bound organic matter, USDA, climate change, nitrogen availability, soil carbon, Natural Resources Conservation Service, agriculture, drought, wet-dry cycling, soil fertility