Corn boost on rye, hold the moisture. That's just what Ralph “Junior” Upton ordered for the 2002 growing season.

With the worst drought conditions in decades, holding the moisture became critical for this Springerton, IL, corn, soybean and wheat farmer. So he planted annual ryegrass as a cover crop in on-farm test plots.

“I thought we had some pretty respectable yields with the small amount of rain we had,” he says. “And I think it's due to the annual ryegrass.”

In field-size test plots on 11 farms — one of them Upton's — Mike Plumer has been testing the virtues of annual ryegrass as a cover crop for the last three years.

With heavy drought conditions, the yield differences were very apparent last fall, says Plumer, a University of Illinois extension agent.

“In no-till corn, where we had ryegrass as a cover crop for three years, we saw an average of 83 bu/acre on eight replications compared to 65 bu/acre for no-till without a cover crop on fragipan soil,” he says. “Where we had conventional tillage on silt loam soil, yields averaged 23-55 bu/acre while the no-till ryegrass cover crop averaged 138.”

The yield difference showed up in soybean fields as well. In the no-till ryegrass plots, soybean yields averaged 25 bu/acre, dropped to 20-21 bu/acre for no-till without ryegrass, and were 15-18 bu/acre in conventional tillage.

The difference is in the roots' ability to take up water, Plumer says. “We noticed that the corn roots were always in mud in the cover-crop plots. Where we had conventional tillage, the roots were never close to any water at all — the water was 2" and 3" below them,” he says. “That's why we saw the huge yield differences this year. I wouldn't normally expect to see that big of a difference.”

Adds Don Wirth of the Oregon Ryegrass Commission: “Organic matter is one of the biggest things you can change to increase water-holding capacity in soil. Ryegrass adds organic matter and increases tilth. It was amazing how that cover crop affected the corn roots.”

Corn roots went as deep as 60" under the no-tilled ryegrass cover-crop plots, 45-48" under no-till without a cover crop and 12-14" under conventional till, says Plumer. In soybeans, the variance was just as great: 30-35" with no-tilled ryegrass, 17-18" with no-till without ryegrass and 8-12" with conventional till.

Annual ryegrass can be aerial-seeded, no-till drilled with a soybean drill or mixed with dry fertilizer and seeded with an airflow applicator from September to mid-October. Upton broadcasts his annual ryegrass with potash in September.

Ryegrass is about 3" tall at maturity, but Upton plans a glyphosate burndown in early April, when it reaches 4-5" in height. Plumer and Upton dug soil pits April 9 last year and discovered that, although the ryegrass was only 4" tall on the surface, the roots were anywhere from 27 to 52" deep.

“I've been working on cover crops for 20 years, and annual ryegrass is the best one I've worked with,” says Plumer. “It's easy to seed and will grow anywhere.”

With annual ryegrass seed priced at $6-8/acre, some farmers may question the cost. “The benefits we're picking up from it — the increased weed control, moisture conservation and the potential for yield increases — would pay for it,” Plumer says. “But this year alone, in the side-by-side field plots where we picked up an 18-bu yield increase in corn, even at $2/bu, that's a $36/acre increase. That will pay for 4-5 years of my seed cost.”

The Downside Of Annual Ryegrass

While annual ryegrass looks pretty good as a cover crop, Mike Plumer, University of Illinois extension, also has a couple of cautions about it.

If you skimp on burndown, ryegrass can resprout.

“We've always controlled it and most of the time one spray controls it,” Plumer says. “But there have been a couple of instances where it took two applications.”

The second problem? Rigid ryegrass, found in California last year, is 100% tolerant to glyphosate and can easily cross with annual ryegrass, Plumer says.

“If that rigid ryegrass starts crossing and seed dealers can't guarantee their varieties are susceptible to glyphosate, we could spread a glyphosate-resistant grass weed. That's a problem.”

Growers should consider annual ryegrass as a cover crop, but should know where their seed comes from, Plumer says.

Plumer doesn't recommend annual ryegrass to growers until it's known if the rigid ryegrass problem will spread. He cautions wheat growers not to grow annual ryegrass because of the intensive weed management required.