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URBANA, Ill. — Farmers apply nitrogen fertilizers to crops to
boost yields, feeding more people and livestock. But when
there’s more fertilizer than the crop can take up, some of the
excess can be converted into gaseous forms, including nitrous
oxide, a greenhouse gas that traps nearly 300 times as much heat
in the atmosphere as carbon dioxide. About 70% of human-caused
nitrous oxide comes from agricultural soils, so it’s vital to
find ways to curb those emissions.
Before they can recommend practices to reduce nitrous oxide and
other greenhouse gases from agricultural soils, scientists first
have to understand where and when they are released. Sampling
soil emissions is labor intensive and expensive, so most studies
haven’t done extensive sampling over space and time. A new study
from the University of Illinois Urbana-Champaign sought to
change that, rigorously sampling nitrous oxide and carbon
dioxide emissions from commercial corn and soybean fields under
practical management scenarios over multiple years. Not only can
this dataset lead to mitigation recommendations, it can refine
the climate models that predict our global future.
“Mitigating agricultural soil greenhouse gas emissions can help
us meet global climate goals,” said study co-author Chunhwa
Jang, research scientist in the Department of Crop Sciences,
part of the College of Agricultural, Consumer and Environmental
Sciences at Illinois. “High spatial and temporal resolution,
large-scale, and multi-year data are necessary to establish
well-informed mitigation strategies. Before our study, these
datasets just didn’t exist.”
Jang and colleagues under Kaiyu Guan’s leadership from the
Agroecosystem Sustainability Center leveraged funding from the
U.S. Department of Energy’s ARPA-E SMARTFARM program to create
the most extensive dataset yet available for on-farm nitrous
oxide and carbon dioxide emissions. They laid out a large
network of gas sampling sites in commercial corn and soybean
fields under conventional, conservation, and no-tillage
management.
Imagine a field fitted with tiny ground-level smokestacks
pumping out gases from the soil. The researchers would visit
with machines to measure the concentration of those gases weekly
or biweekly throughout the season for two years. Smokestacks
that consistently pumped out high concentrations of gases were
termed hot spots. Hot moments were when concentrations rose
across most or all of the smokestacks after events like rainfall
or fertilizer applications.
“We found carbon dioxide flux was similar across individual
fields, sites, and years, or even between corn and soybean
systems,” Jang said. “These results tell us that carbon dioxide
emissions are consistent and that high spatial resolution
sampling is likely sufficient to estimate field-wide flux.”
Nitrous oxide, on the other hand, was anything but consistent.
Not only did the amount of nitrous oxide at a particular
smokestack swing dramatically from one sampling session to the
next (hot moments), the researchers found that they couldn’t
predict where in the field they’d find hot spots on any given
date.
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“Spatially and temporally, nitrous
oxide was very variable,” Jang said. “One day, point A would be
having a hot moment, and then at the next measurement, we’d find hot
moments at points B and C. The hot spots were just moving around.”
This finding is important because if previous studies only sampled
at a couple of spots or on a couple of dates, their estimates for
nitrous oxide flux could be wildly off. These measurements inform
the global climate models that tell us how soon we will reach
critical tipping points, so it’s immensely important that they’re as
accurate as possible.
“This project enabled us to capture spatio-temporal and management
variation to provide gold standard data and a platform for
validating field-level greenhouse gas emissions,” said study
co-author DoKyoung Lee, professor in crop sciences at Illinois.
“This is necessary for sustainable practices to secure both food and
bioenergy demand and minimize emissions to the atmosphere.”
The results also revealed how management and cropping systems
influence greenhouse gas emissions. Carbon dioxide emissions were
similar for corn and soybean and for conservation and no-tillage,
but conventional chisel tillage and continuous corn saw higher
concentrations. Nitrous oxide, on the other hand, was far higher in
corn than soybeans under conservation and no-tillage, and nearly off
the charts in continuous corn under chisel tillage.
“We may not be able to predict where and when nitrous oxide will
spike, but we do know management makes a difference,” Jang said. “In
continuous corn, farmers have to apply high amounts of nitrogen
fertilizer, which converts into nitrous oxide. And conventional
tillage interrupts the soil surface and releases gas. We know what
to do to mitigate it.”
The study, “Spatial variability of agricultural soil carbon dioxide
and nitrous oxide fluxes: Characterization and recommendations from
spatially high-resolution, multi-year dataset,” is published in
Agriculture, Ecosystems, and Environment [DOI:
10.1016/j.agee.2025.109636]. Authors include Nakian Kim, Chunhwa
Jang, Wendy Yang, Kaiyu Guan, Evan DeLucia, and DoKyoung Lee.
Lee is also affiliated with the Institute for Sustainability,
Energy, and Environment, the Agroecosystem Sustainability Center,
the Center for Advanced Bioenergy and Bioproducts Innovation, the
Center for Digital Agriculture, and the National Center for
Supercomputing Applications at U. of I.
Sources:
Chunhwa Jang, cjang8@illinois.edu;
DoKyoung Lee, leedk@illinois.edu
[Lauren Quinn | Aces News]
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