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URBANA, Ill. — While the majority of Midwestern farmers rotate
corn and soybeans, commodity prices and corn yield advantages
compel some to plant corn year after year. Although foundational
research on the benefits of corn-soybean rotation goes back
decades, University of Illinois Urbana-Champaign scientists are
working to address remaining holistic questions about crop
yield, environmental impacts, and economic returns under various
crop rotation scenarios.
In a new study, researchers from the university’s Agroecosystem
Sustainability Center and the College of Agricultural, Consumer
and Environmental Sciences used the sophisticated agroecosystem
model ecosys to explain why corn yield is higher after soybean
at normal nitrogen fertilization rates; how corn-soy rotation
impacts soil greenhouse gas emissions and nitrogen leaching; and
when corn-soy rotation is most economically advantageous.
“We found that while corn-soy rotation can boost corn yields and
reduce nitrogen fertilizer needs, the benefits come with nuanced
environmental and soil carbon trade-offs,” said study leader
Kaiyu Guan, founding director of the ASC and ACES Levenick
Professor in the Department of Natural Resources and
Environmental Sciences at Illinois.
Fertilizer rates determine corn yield boost from rotation
After training the ecosys model on a decade’s worth of
Department of Crop Sciences field trials with varying rotations
and nitrogen fertilizer rates, the researchers were not
surprised to find corn grown after soybeans consistently yielded
about 6.4% more, on average, than continuous corn, at standard
nitrogen rates (151 kilograms of nitrogen per hectare).
Diving deeper, the team found that the lower biomass and faster
breakdown of soybean residue left the soil surface more exposed
in spring, when corn is planted. Exposed soils warm more
rapidly, which in turn causes soil microbes to mineralize more
nitrogen from organic matter, providing a source of available
nitrogen for young corn plants — an effect much like starter
fertilizer commonly used by farmers. The researchers found this
led to greater corn yield by the end of the season.
However, this advantage decreased with higher nitrogen
fertilizer rates.
“The more nitrogen you add, the less yield benefit you get from
rotation,” said the study's first author Ziyi Li, research
scientist at ASC. “In some cases, the yield boost nearly
disappears.”
Rotation reduces emissions, but affects soil carbon and
nitrogen loss
From an environmental standpoint, corn-soy rotation helped
reduce nitrous oxide and ammonia emissions from soils. But the
fast-decomposing soybean residues led to an overall reduction in
soil organic carbon compared to continuous corn.
Not surprisingly, nitrogen leaching was lower in soybean years
due to the absence of fertilizer application. However, the fact
that there was still nitrogen leaching under soybeans points to
the importance of nitrogen mineralization from organic matter.
Leaching increased in subsequent corn years when decomposed
soybean residues released nitrogen into the soil.
“These results underscore a key trade-off,” Guan said. “Rotation
improves some sustainability metrics while compromising others,
especially under typical fertilization practices.”
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Economic returns favor rotation, but depend on fertilizer use
and market prices
Using historical commodity prices, the researchers found that
corn-soy rotation offered higher economic returns — up to
$458/acre ($1,133/hectare) more than continuous corn — at low
nitrogen fertilizer rates (45 pounds/acre) and under typical
market conditions (soybean: $11/bushel, corn: $4.50/bushel, and
N fertilizer: $193/Mg ($175/short ton) UAN). But under high
nitrogen inputs and market scenarios with elevated corn prices,
this advantage was significantly reduced or even reversed.
“The extent to which one cropping system outperforms the other
in terms of net agronomic benefits depends on more than just
corn yield and nitrogen fertilizer usage, but also needs to
consider soybean yield and market-driven prices, including
fertilizer, grain, and costs such as machinery,” Li said. “Such
comprehensive economic assessments can help farmers make
informed decisions about crop sequences, especially in response
to market fluctuations, and inform insurance products and
conservation initiatives accordingly.”
No universal approach
The study underscores the importance of tailoring nitrogen
management to balance profitability and sustainability. Lower
fertilizer rates in corn-soy rotation compared with continuous
corn can maximize economic return while mitigating some
environmental impacts, but farmers must weigh these benefits
against potential declines in soil organic matter and greater
nutrient leaching.
“Our work gives farmers and policymakers a more holistic view of
organic matter, nitrogen, and yield outcomes,” said co-author
Andrew Margenot, associate professor in crop sciences at
Illinois. “We’ve known that these components matter and how they
respond individually, but tying them together to show the
interconnectedness is key.”
Additionally, Margenot points out that this work underscores the
need to consider long-term changes in organic matter given its
importance as a source of nitrogen for crop uptake.
“These results are consistent with increased nitrogen
mineralization under soybean than corn, and declines in organic
matter being driven by soybean in the corn-soybean rotation,” he
said.
Decades of research have pointed to advantages of crop rotation
in terms of yields, reduced fertilizer needs, and soil health.
The new study provides a robust scientific rationale for
rotation and fills a previous knowledge gap by quantifying the
agricultural outcomes of corn-soy rotation in detail. Despite
the environmental tradeoffs discovered by the team, the economic
analysis demonstrates that crop rotation is profitable,
especially at lower fertilizer rates.
The paper, “Comparing continuous-corn and soybean-corn rotation
cropping systems in the U.S. central Midwest: Trade-offs among
crop yield, nutrient losses, and change in soil organic carbon,”
is published in Agriculture, Ecosystems and Environment [DOI:
10.1016/j.agee.2025.109739]. The research was supported by the
Illinois Nutrient Research & Education Council, Illinois Soybean
Association, the National Science Foundation, the NASA Acres
Program, the U.S. Department of Energy’s ARPA-E SMART-FARM
program, and the USDA National Institute of Food and
Agriculture.
Sources:
Kaiyu Guan, kaiyug@illinois.edu;
Ziyi Li, ziyili5@illinois.edu;
Andrew Margenot, margenot@illinois.edu
News writer:
Lauren Quinn, 217-300-2435, ldquinn@illinois.edu]
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