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 “Most research on soil microbial health has been done in a lab
or greenhouse setting, or in short-term field experiments. Here
in Illinois, we have a fantastic opportunity to look at what
long-term farm management does to the soil,” says Maria Villamil,
associate professor in the Department of Crop Sciences at the
University of Illinois and co-author on a new study published in
Science of the Total Environment.
Leveraging a 20-year field experiment, Illinois crop scientists
demonstrated significant risks associated with continuous corn
rotations, both for the soil microbial community and for
environmental health on a larger scale.
“In order to maintain yield levels under continuous corn, more
inorganic nitrogen is required, thereby intensifying the
nitrogen cycle and causing a dangerous loop,” says Gevan Behnke,
lead author on the study and postdoctoral researcher in crop
sciences. “The result is acidification and potential increases
in nitrogen loss and harmful nitrous oxide emissions.”
Rotating corn with soybean for a year or more tempers the
effect, the researchers found.
Illinois crop scientists first planted corn and soybean at the
experimental site in 1996, with some fields in continuous corn,
others in continuous soybean, and others rotating annually
between the crops. Within each cropping system, fields were
either not tilled or chisel-tilled each year.
Behnke analyzed soil samples taken from each field type in 2015
and 2016, extracting DNA and measuring physical and chemical
properties.
“The DNA analysis was important because a lot of problems are
related to the nitrogen cycle, whether that’s nitrous oxide
emissions, nitrate leaching to water bodies, or just a toxic
build-up of nitrogen in the soil,” Behnke says. “Therefore, we
studied genes and microbial groups associated with fixation,
nitrification, and denitrification.”
The process of microbial nitrification turns ammonia fertilizer
into nitrate, a much more mobile form associated with runoff and
leaching. Denitrification, on the other hand, turns nitrate into
gaseous forms, including nitric and nitrous oxide, a potent
greenhouse gas.
Putting all the data together, the researchers found continuous
corn increased soil organic matter and acidity, and led to an
increase in microbes involved in both nitrification and
denitrification. The researchers found the opposite pattern in
continuous soybean, and intermediate results in the corn-soybean
rotations.
“Previous studies have shown continuous corn emitting more
greenhouse gases, but our study explained why on a microbial
level,” Behnke says. “It was good to see our results match up
like that.”
No-till management increased soil organic matter, which led to
more acidic soils and an increase in the abundance of bacteria
that turn ammonia into nitrate.
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“Nitrogen is left on the soil in no-till fields,
whereas tillage can really spread out that nitrogen throughout the
top 10 centimeters. However, tillage by itself wasn’t as strong a
driver of microbial abundance as crop rotation,” Behnke says.
“Ultimately, reducing the number of corn years will help decrease
the negative effects of continuous corn on soil health.”
The first-of-its-kind study not only provides
important foundational information about soil health in agronomic
systems, it also establishes a baseline for future research.
Villamil’s larger research program seeks to understand how cover
crops affect soil microbial activity when added to corn and soy
rotations. Her team recently published an analysis of existing
research on the topic and completed two years of field sampling with
cover crops at the long-term site.
“Big picture, we’re looking at whether there’s a potential to
manipulate soil health and the microbiome with cover crops. In
Illinois, we’re kind of stuck with this system of corn and soybean.
Our results indicate alternating corn with soybean might help, but
they're really very similar crops, both very extractive,” Villamil
says. “We need to increase the diversity of crops either in time or
in space, and I think cover crops is one of the solutions we have at
this moment. We need to gain awareness.”
She adds that improving soil health is of the utmost importance,
regardless of the method.
“Soil health has a lot of linkages with environmental health, mainly
through greenhouse gas control, but also to human health. Recent
research finds correlations between soil microbial biodiversity and
the human microbiome. So there's a strong need to really understand
soil health functioning within different agricultural settings
because of these strong links with environmental health and
potentially human health,” she says. “Healthy soil supports healthy
life.”
The article, “Acidification in corn monocultures favor fungi,
ammonia oxidizing bacteria, and nirK-denitrifier groups,” is
published in Science of the Total Environment [DOI:
10.1016/j.scitotenv.2020.137514]. Authors include Gevan Behnke,
Maria Zabaloy, Chance Riggins, Sandra Rodriguez-Zas, Laibin Huang,
and Maria Villamil. The research was supported by the USDA National
Institute of Food and Agriculture.
The Department of Crop Sciences is in the College of Agricultural,
Consumer and Environmental Sciences at the University of Illinois.
[Sources: Gevan Behnke, Maria
Villamil
News writer: Lauren Quinn] |
