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 New University of Illinois research integrates field data and
advanced mathematical modeling to understand how cover crops
affect soil water, nitrogen, and oxygen dynamics, and may
compete with summer cash crops.
“Cover cropping requires management. Otherwise cover crops
compete with corn and soybean and can cause some yield loss.
With proper management, however, farmers could use the right
cover crop types and find the optimal growth window to plant and
terminate cover crops to achieve benefits and minimize negative
impacts on cash crops,” says Kaiyu Guan, founding director of
the Agroecosystem Sustainability Center, associate professor in
the Department of Natural Resources and Environmental Sciences,
and Blue Waters professor at the National Center for
Supercomputing Applications at the University of Illinois. He is
also senior author on a new paper published in Field Crops
Research.
Guan’s insights are based on a sophisticated mathematical model
validated by five years of experimental field data collected
from multiple sites across Illinois by Maria Villamil, a
co-author of the paper and professor in the Department of Crop
Sciences at Illinois. The process-based model aims to identify
the underlying drivers of cover crop effects on cash crop yield,
including cover crop type; termination timing; and soil factors
such as water, nitrogen, oxygen, and soil temperature.
“Process-based models validated with field data have multiple
advantages compared to field experiments alone,” says Ziqi Qin,
doctoral student working with Guan and lead author on the study.
“Most field experiments only focus on final variables such as
cash crop yield or cover crop biomass, and can take years to
conduct.
“Process-based modeling methods can simulate intermediate
variables that are difficult to measure in field experiments,
such as processes taking place in the soil. Models validated
with field-based measurements can help optimize cover crop
decisions, such as cover crop types and planting and termination
time, through scenario simulations.”
By incorporating intermediate factors, the model explained why
cover crops interfere with cash crop yield. Essentially, the two
types of crops compete for common resources in the soil,
including water, nitrogen, and oxygen. But context matters and
the impacts are species-specific.
Soybean yield was unaffected by either type of
cover crop, probably because soybeans put their own nitrogen
into the soil. For corn, competition for water is heightened in
dry years, according to the model, and the later cover crops are
terminated, the less nitrogen is available for cash crops.
When the model focused on cover crop type, it found non-legume
species, such as annual ryegrass and cereal rye, reduced corn
yield by 0.9 to 6.9%. However, the nitrogen-fixing legume hairy
vetch didn’t impact corn yield under high-nitrogen conditions.
These findings are consistent with field observations across the
Midwest and worldwide, and Guan says that lends credibility to
his Midwest-centric modeling study.
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The model found termination timing can be just as
important as species. Late termination of non-legume cover crops –
just a day before planting – resulted in more corn yield loss than
terminating a month ahead of planting.
But that’s less time for the cover crop to do its work.
“There is a tradeoff between cover crop benefit and cash crop yield.
If we terminate earlier, the cover crop won’t affect cash crop yield
as much, but it will accumulate less biomass and potentially take up
less soil nitrogen. So we have to balance those two factors,”
Villamil says.
The model also identified other factors that negatively impacted
cash crops, including cooler soil temperatures under cover crop
biomass and less soil oxygen availability.
“You have to understand the process, and that part has been missing
from other research in this area,” Guan says. “For example, I don't
think people fully appreciate the impact of oxygen in the soil,
which turned out to be an important factor in our model. And many of
these factors change in context of weather, climate, and soil. All
these are worth more systematic studies.”
Guan notes programs like the USDA’s Pandemic Cover Crop Program,
which reduces crop insurance premiums for farmers who grow cover
crops, may incentivize more of the 95% who don’t to get on board
with the conservation practice.
“In addition, with the increase in the private carbon credit market,
there could be an increase of cover crop adoption in a significant
way. We probably will see a surge. So this makes this topic
extremely relevant and important,” he says. “We’re here to tell
farmers how the science works, and then properly guide them to gain
the benefit of cover crops.”
The article, “Assessing the impacts of cover crops on maize and
soybean yield in the U.S. Midwestern agroecosystems,” is published
in Field Crops Research [DOI: 10.1016/j.fcr.2021.108264]. Additional
Illinois co-authors include Wang Zhou, Bin Peng, Lowell Gentry,
Andrew Margenot, German Bollero, and Ziyi Li. Zhenong Jin,
University of Minnesota; Jinyun Tang, Lawrence Berkeley National
Laboratory; and Robert Grant, University of Alberta are also
co-authors.
Funding was provided by the Illinois Nutrient Research and Education
Council, the National Science Foundation, USDA’s National Institute
for Food and Agriculture, and the Foundation for Food and
Agriculture Research.
The Agroecosystem Sustainability Center (ASC) aims to be a
world-leading innovation powerhouse in advanced monitoring and
modeling of agroecosystems to improve sustainability under climate
change. ASC is jointly funded by the Institute for Sustainability,
Energy and Environment (iSEE), the College of Agricultural, Consumer
and Environmental Sciences (ACES), and the Office of the Vice
Chancellor for Research and Innovation (OVCRI) at the University of
Illinois. The Department of Natural Resources and Environmental
Sciences is in the College of ACES.
[Sources: Kaiyu Guan, Ziqi Qin, Maria
Villamil,
News writer: Lauren Quinn] |
