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 a shot.

“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 a pathogen?

“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.”

Reducing Nematodes

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 ability.

“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.”

Higher Yields

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.”