CARBONDALE, Ill. — Researchers have for years documented
that some cover crops can dramatically reduce soybean cyst nematode populations.
Soon they’ll be able to quantify that finding.
Jason Bond, an associate professor in plant, soil and
agriculture systems at Southern Illinois University, is among others at the
university’s ag college who will be examining soil samples using a new procedure
called metagenomics, in which gene sequencing provides a window into the study
of microorganisms in the soil.
“We’re going to start taking samples and sequencing what’s
in the soil to see what effect cover crops are having on pathogens, but also
what we consider the beneficial organisms,” Bond said. “We can answer some
questions with these cover crops that we couldn’t answer four or five years ago
because (gene mapping) was so expensive.”
He was involved, along with retired SIU professor Mike
Schmidt, in an earlier project examining benefits of cover crops. Using research
plots, they saw soybean yield increases and reduced nematode populations
following canola and rapeseed grown as cover crops.
Canola at the time was a promising new crop in Illinois,
prompting the study. But things didn’t work out well for most farmers giving it
“They had a big push for canola back in the ‘90s. They just
happened to put it out in a year when they had massive winterkill, so it soured
a lot of farmers on doing it,” Bond said. “When they knew they were going to try
to get producers to grow canola, they wondered what happens if you have another
situation with winter kill. Are there other benefits for the soil or maybe even
“Even if you have winterkill, you might get some return on
your investment to go into your soybean crop. That was Mike’s approach. I was
interested in that angle, too. Jointly we decided to look at that for cyst. The
whole idea on mustards was bio-fumigants. That came out of research in the
Pacific Northwest. It all came together at one time.”
The canola resulted in a reduction in nematode populations
as much as 50 percent in some plots. That is roughly equal to the benefit
achieved by rotating corn and soybeans.
“With corn, sometimes we can cut the nematode population in
half,” Bond said. “You don’t eliminate it, but you definitely reduce it 20 to 30
percent, and with other strips, 40 to 50 percent.
“That second year of corn, you don’t get the same bang for
your buck. It’s a diminishing return. You’re still going to reduce it, but not
nearly as dramatic as the year before.”
Cover crops have other benefits, so their effect on cyst
nematodes is a plus. And with more and more growers using cover crops, the
research has been revived.
Ryegrass also has shown a similar nematode-killing
“Ryegrass also has the capability of hindering a lot of weed
germination,” Bond said. “We never were able to document why, but we would get a
reduction. We didn’t get the same response when we did wheat. And it had no
impact on cyst one way or another.”
The cover crop studies resulted in soybean yield increases
of six to seven bushels per acre. Because of the expense of genetic testing,
Schmidt and Bond were limited in their ability to quantify the results. That is
all changing this year.
“We never carried it to the next step. That was seven or
eight years ago when we did those studies,” Bond said. “We now have the
capability with all these molecular techniques that we can take a soil sample
and see all the DNA. It will tell you not only what you have, but how much is
there. We have not deployed that approach until just this year.
“This is a major project we manage out of SIU. The United
Soybean Board is heavily involved. We have better molecular tools for seedling
diseases. It’s now very reasonable to do this massive sequencing.”
Bond stressed that cover crop production is certainly no
magic bullet. Among other things, there is evidence that some clovers may harbor
cyst nematodes. It also is a management-intensive practice.
“It’s not an easy thing to get set up. You’ve got mixed
species to try to get established,” Bond said. “You also have to be able to the
kill the thing and plant your own crop into it. It’s very important to choose
the right species for that. You do need agronomists, plant pathologists and soil
fertility people. All this is coming together at SIU and other universities,
where we’re looking at the true benefits of cover crops.”