Carbon credits are a subject of growing interest in agriculture. The idea sounds simple enough: if a farmer can show that their soil is capturing greenhouse gas emissions, they can generate additional revenue by trading the resulting carbon credits on bioenergy markets. But proving that carbon is actually there, and staying there, is a much harder problem. For the past five years, DWFI Director of Research Christopher Neale and his team have been part of a U.S. Department of Energy-funded effort to investigate whether the science supports the promise of carbon sequestration in agriculture.
Why cropland matters
Agriculture is unusual in that it can be both a source of greenhouse gas emissions and one of the largest potential sinks for carbon. That dual role is what makes farmland such a focal point for carbon capture, and why the DOE wanted hard data from real production fields rather than theoretical models alone.
For example, overapplying nitrogen fertilizer can release nitrous oxide, while soil tillage can disrupt soil structure, releasing stored carbon.
Alternatively, plants capture atmospheric carbon dioxide through photosynthesis and store it in plant biomass and grain as well as the soil as organic matter. Generally, greater plant biomass (and surface area) equates to higher levels of carbon storage. This is what makes corn and soybean fields particularly promising candidates for carbon sequestration. In addition, about a third of U.S. corn is used to produce ethanol, which generally emits fewer greenhouse gases over its full lifecycle than traditional fossil fuel.
The project monitored fields representing thousands of acres of both irrigated and rainfed corn and soybean fields that supply grain for ethanol production across Nebraska, Iowa and Minnesota, capturing a diverse range of climates, soil types and cover crop practices.
By comparing these systems, the research team could start to see which practices sequester carbon most efficiently and release less greenhouse gases, as well as which trade-offs come with each approach.
Measuring the invisible
To track carbon accurately, the team layered several types of measurement on top of each other. Eddy covariance towers measured carbon dioxide and water vapor exchange across each field, while DOE funding allowed the team to add gas analyzers capable of measuring methane and nitrous oxide fluxes—both far more potent greenhouse gases than CO2.
The project began and concluded with deep soil core sampling, reaching about four feet below the surface. Because soil carbon accumulates slowly, this five-year window is essential to distinguish real signals from statistical noise.
What surprised researchers
Neale shared a few findings from the study that stood out:
A record yield told a more complicated story. In 2021, one Nebraska field set a yield record—273 bushels per acre (1.84 metric tonnes per hectare) of corn. That year showed strong carbon capture. But the following year, when the field rotated to soybeans, the system actually lost carbon, as measured by the eddy covariance towers. Soybeans are a slightly less efficient carbon-capturing crop than corn, and the corn stover left on the surface from minimum-till practices broke down during the soybean year, releasing CO2 back into the atmosphere. Across the full two-year rotation, the field still captured carbon—just far less than the corn year alone would suggest. To verify these findings, the team will also analyze five years of soil core data.
Methane behaved differently than expected. Rather than being a net source, a typical irrigated corn production field actually captured methane—a result the team confirmed using automated soil chambers placed under the crop canopy.
Soil type drives outcomes. Carbon capture varies meaningfully with soil physical properties. Clay-loam soils tend to hold more carbon than sandy soils, and the same property that helps soil retain water also helps it retain carbon and nutrients—one reason a rainfed Minnesota plot with lower biomass production may show different results than an irrigated Nebraska field.
Why the models needed real-world data
The DOE's existing carbon accounting tool relies on default values when field measurements aren't available. These default values are generic assumptions. When Neale's team plugged in actual field measurements, results diverged significantly. This gap is what the DOE aimed to close: better field data allows models to more realistically project carbon outcomes.
The water and carbon connection
The Nebraska field's record 2021 yield wasn't just a good climate year—irrigation scheduling, guided by DWFI's SETMI model, helped avoid plant stress during pollination, a critical window for corn yield. Proper irrigation management cuts both ways: under-watering stresses the crop, while over-irrigating leaches fertilizer below the root zone, where it becomes both unavailable to the plant and a potential source of nitrate contamination in groundwater. Getting that balance right supports yield, and yield is directly tied to how much carbon a field captures.
What's next
Originally planned as a three-year project, the team’s work extended to five years due to pandemic-related challenges. The team is now preparing a final report and peer-reviewed publications, which required multiple years of data to establish credible patterns. Based on the preliminary data, Neale sees the potential of net carbon capture in agriculture and the adoption of practices and production systems to enhance this capture.
As for when or how the DOE might translate this research into a real carbon credit program for farmers, Neale was candid that the timeline is uncertain, although he hopes the research will eventually inform policy when conditions allow.
Looking ahead, Neale sees the next phase of research extending to additional crops and production systems, with a focus on optimizing fertilizer and water use—capturing more carbon and reducing pollution at the same time. Getting that knowledge into farmers' hands, he notes, is where extension and university partnerships will play a critical role. The specialized equipment used in this study—eddy covariance towers, automated soil chambers, gas analyzers—is too costly to deploy on every farm. The real value of the project, Neale says, is using it to refine the models so the underlying science can scale far beyond the research fields where it started.
Listen to the full interview on the Water for Food Podcast » https://waterforfood.nebraska.edu/our-work/communication/podcast