Cover crops seeded into silage corn won't reduce yields, will hold soil and nutrients on sloping land and can jump-start the next year's forage crop.

That's what John Grabber hopes to prove with his research on red clover cover crops seeded into silage corn.

“Farmers are concerned, if they're going to use cover crops, that they will hurt their corn crop yields,” says the research agronomist with the U.S. Dairy Forage Research Center, Madison, WI. “It's encouraging that some cover crops are getting comparable silage yields to no cover and, in some cases, better yields.”

Grabber, at this point, has researched which cover crops are most effective in his southern Wisconsin region. Red clover has been the most successful, helping to increase corn silage yields and provide a half ton/acre of ground cover after the corn is harvested.

“We'd like to see if we could also keep the red clover in production the following year as a forage crop and get full production-year yields. That could make it economically a more attractive option.”

The next step in his research is to find practical ways for growers to seed red clover into corn. He no-till drilled it between the rows of 6"- to 12"-tall corn. Although seed could be broadcast after cultivation, clover establishment would be more erratic than if a no-till drill were used, he explains.

Growing corn in a living mulch of kura clover is also a promising way to protect the soil. “It takes two years to get kura fully established,” says Grabber. “Then you can suppress it with herbicide and plant corn into it. Once you're done growing the corn, you can harvest or graze kura for a year or more before again growing corn in it.”

Kura can last 30 years or more, Grabber says. “That's probably the strongest reason to grow it.” Corn grown in kura yields well in normal or wet years, but not during prolonged dry periods, he adds.

Grabber also tried interseeding Italian ryegrass, but it depressed corn silage yields. Fall-seeded winter rye didn't hurt corn yields when it was killed early enough in spring.

“A main reason I did the study is that more farmers are switching to corn silage,” says Grabber. “A lot of land on dairy farms is sloping and subject to erosion, so I wanted to compare alternative cover crops.”

His 2003 results showed corn silage yields ranging from 8.2 to 10.3 tons dry matter/acre. Fields with red clover yielded the most; those with ryegrass, the least. In 2004, yields ranged from 7.4 to 8.9 tons DM/acre and tonnage was greater with clover and no cover crop than with rye or ryegrass.

“There is some risk with interseeded red clover,” he cautions. “It can die out in corn if conditions get really dry for prolonged periods in late summer. In that case, the farmer would reseed red clover the following spring as would normally be done. Alfalfa, which is more drought-tolerant, could also be interseeded into corn as a cover crop and grown for forage production the following year.”

Italian Ryegrass Works For Northwestern Growers

For years, Pacific Northwestern silage corn producers have been air seeding Italian ryegrass between corn rows as a cover crop, says Shabtai Bittman, research scientist with Agriculture and Agri-Food Canada.

“In Washington state's main dairy county, which is just across the border from us, there is something like a 70% adoption rate,” says Bittman, based in British Columbia.

Environmental regulators are strongly urging this soil-saving technique, and “farmers are quite on-board with doing this,” he says. “In our region it has taken longer. Of all the corn acres that go in, something like 10% have cover crops."

That's because custom farming is less prevalent in that Canadian region and farmers don't have the specialized equipment.

Most Washington custom operators can seed cover crops with air seeders mounted on cultivators.

“It doesn't add a farm operation,” Bittman adds. Ideally, air seeding of ryegrass should be done when corn is at the three- to six-leaf stage. It's more commonly done at about five to nine leaves, because it can be tied in with other operations, he says.

“The advantage of this system is that you don't have to do any of that work in the fall. The relay ryegrass crop is already growing when the corn is harvested and produces more before the onset of winter than fall-seeded winter wheat or fall rye. Ryegrass has a higher quality as spring pasture or stored feed.

“In our trials, this system has the maximum amount of ability of soaking up nitrogen in the fall,” he adds. The downside is getting the cover crop off during the busy spring season, he explains. “Some of the grass is plowed under, which is not ideal. What you want to do is harvest the grass and feed it to the cows and reduce your imports of feed.”