Interseeding alfalfa into silage corn can double first-year yields of alfalfa, according to Wisconsin research.

In plot trials, alfalfa was no-till drilled into fields that had been planted the day before with corn, says John Grabber, a USDA-ARS agronomist working at the U.S. Dairy Forage Research Center.

“The main reason to try this system was to see if we could skip the normal low-yielding establishment year by establishing alfalfa during the final year of corn,” he says.

In 12 years of research, Grabber’s looked at interseeding cover crops into corn that also can be used as forage. He’s tested grasses and clovers and, most recently, alfalfa with University of Wisconsin’s Mark Renz, a weed specialist, and Joe Lauer, a corn agronomist.

“Weed management is a big issue,” says Renz, because two crops need to be considered and only a handful of herbicides are registered for both. The trials utilized Roundup Ready corn and alfalfa or Clearfield corn and conventional alfalfa, which are tolerant of Pursuit herbicide.

Corn was no-till planted into 30” rows 1½-2” deep in early to mid-May and leafhopper-resistant alfalfa was drilled in the next day at ¼-½” deep. “With many drills, a farmer can plant alfalfa with or against corn rows with little risk of disturbing corn,” Grabber says.

When the alfalfa was 3-8” tall, a growth regulator was applied.

“The problem has always been, if you plant alfalfa with corn, the two crops compete too vigorously with each other. This often leads to alfalfa stand failure and reduced yields of corn,” Grabber adds.

But applying a growth regulator called prohexadione to alfalfa doubled its survival under corn, possibly because it increased root growth and stress resistance of alfalfa seedlings, he says. Also known as Apogee, it’s currently labeled only for apple, peanut and grass seed production. It’s unclear whether the manufacturer, BASF, will register it for alfalfa and corn, so the researchers are testing other plant growth regulators for effectiveness.

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Even with the growth regulator, the Wisconsin trials showed that corn yields were reduced by 7% when alfalfa was established with it, he says.

The corn yield loss, however, is “quite a bit less than has been reported in the literature (of similar studies),” Grabber says. He thinks careful nitrogen management has had something to do with that.

Normal rates of nitrogen were applied, half banded at corn planting and the rest sidedressed, “to give the corn the best chance of getting at that nitrogen – because alfalfa will use it, too. We’re trying to manage nitrogen in a way that favors corn.”

“We’ve had success three out of four years getting both of them to successfully establish,” Renz adds. “Some years when the corn is really competitive, we need every little trick in the book to get the alfalfa to survive. In other years, like in 2012 when we had a really bad drought, we didn’t need to do anything. The alfalfa persisted just great.”

To further refine the system, the scientists have recently been comparing different rates of growth regulator, sprayed as single or split applications on alfalfa.

The effects of alfalfa and corn seeding rates on crop establishment and yields are also being examined. New corn hybrids with increased drought tolerance could help make this system work even better, Grabber says. “They could help reduce yield hits on corn because corn and alfalfa are competing for water.”

Growers may be concerned about damage to alfalfa stands at corn harvest, he points out. “But the alfalfa is quite resilient. Seedlings can get plastered over by wheel traffic, and they seem to bounce back pretty well.” There could be damage in years with wet falls and rutted fields, Grabber admits.

“I think the system could work for red clover, too. You just have to get the right match of herbicides that are compatible. In the one year we studied it, red clover was successfully established in corn without any effect on silage corn yields.”

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