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Use Rye as a Companion Crop for Soybeans

Rye suppresses weeds, controls erosion, and offers management options.

Rye’s weed-fighting skills along with its cover crop benefits make it a particularly good companion crop for soybeans.

“Soybeans and rye complement each other really well,” says Mike Ostlie, agronomist at the North Dakota State University’s Carrington Research Extension Center (CREC). “Rye adds a lot of things to soybeans that really complete a good production system. You can use rye as a weed-management tool because it suppresses weeds that are becoming increasingly resistant to glyphosate.

“I’ve also heard reports from growers that they were able to plant farther into saline soils in fields that had been planted to rye the year before,” he says. “Rye’s extensive, fibrous root structure uses moisture and provides firm footing for equipment.”

While evaluating rye in a CREC study, Ostlie saw firsthand its aptitude for controlling erosion.

“When you plant rye in the fall, you get wind erosion over winter, of course,” he says. “But the rye also provides erosion control during the spring seeding of the soybeans. In the absence of a cover crop, the rolling of fields after planting soybeans comes at a time when strong spring winds carry away unprotected soil. Rye protects the soil surface from wind erosion.”

How Rye Can Fit Soybeans

The CREC study examined several ways winter rye could be incorporated into a soybean rotation. A comparison of rye-removal strategies evaluated included the following:

  • Weed control.
  • Yield of rye harvested for both forage and grain.
  • Yields of soybeans when rye was terminated or harvested for grain or forage.

In each of the study treatments, rye was planted in late September. The rye grew rapidly early in the spring and was in the boot stage when the soybeans were planted on June 3.

When rye was killed prior to soybean planting, soybeans yielded 48 bushels per acre in the NDSU trial.

No preemergent herbicide was applied to the treatments so that rye could be evaluated for its weed-suppression ability in the early part of the growing season. Kochia control during this time ranged from 30% to 70% across the trial.

“The weed suppression was largely in the form of reduced kochia growth and vigor, but it wasn’t necessarily in reduced plant numbers,” says Ostlie. “Soybean growth and development did not appear to be influenced by the presence of the rye or by the removal strategies.

Rye harvested for forage in mid-June helped spur a double crop of 5,259 pounds per acre of forage and soybean yields of 36 bushels per acre in the NDSU trial.

“Overall, the rye and soybeans grew well together,” he says. “The rye recovered remarkably well from the soybean planting operation, and the soybeans grew through the rye canopy with ease for the first month or so through the time the rye flowered.”

A supplemental treatment of glyphosate was applied to soybeans in mid-July. By then, the rye had been removed or the plants had matured, thus, opening up the canopy and permitting the kochia to grow more vigorously.

Following are the five most viable rye-removal strategies the study evaluated.

  1. Rye tilled. Rye was tilled at the end of May. The soybeans yielded 37 bushels per acre.
  2. Rye sprayed early. Rye was sprayed prior to soybean planting, and soybean yield was 48 bushels per acre.
  3. Rye mowed. The mowing was done in mid-June when the rye was beginning to head. The rye residue was left on the field. Because the soybeans were at the first-leaf stage at the time of mowing, they were not harmed by the cutting equipment and were able to recover from the wheel traffic. The mid-August herbicide application controlled rye regrowth. The soybeans yielded 37 bushels per acre.
  4. Rye harvested for forage. Harvesting of the rye for forage was done in mid-June, when soybeans were still in the first-leaf stage. The rye yielded 5,259 pounds of forage per acre or 2,155 pounds on a dry-matter basis. Soybean yield was 36 bushels per acre.
  5. Rye sprayed late. When rye was sprayed at heading in mid-June, soybean yield was nearly 33 bushels per acre.

The check to all treatments was a soybean plot where no rye had been planted. Like the other plots, these soybeans received no preemergent herbicide but were treated with glyphosate in mid-July. The soybeans yielded 29 bushels per acre.

“Aided by the application of glyphosate in mid-July, most treatments continued to maintain a high level of weed suppression, even though the rye had been removed quite some time earlier,” says Ostlie. “The most impressive treatment in terms of late-season weed control was the application of glyphosate at the heading of the rye. This data suggests that the longer the rye remains in the field up until heading, the better the weed control.”

How to Make Rye Work

Rye fights weeds because of chemicals it produces that have an allopathic, or suppressing, effect on the development of other plants.

Yet, in a study of winter rye at the Carrington (North Dakota) Research Extension Center, there was no suppression of soybeans planted into spring rye growth.

“This could be due to the soybean planting operation clearing a path around the soybean root zone or to soybeans being resistant to rye allelopathy,” says agronomist Mike Ostlie.

Study results suggest that the effectiveness of rye’s weed control is enhanced when rye is left to near maturity. “The longer the rye stays in the soybeans, the better – as long as moisture isn’t a factor,” says Ostlie.

Once the rye starts heading, however, its allelopathy decreases. “We found that as soon as rye starts to head out, it loses its ability to suppress weeds,” he says.

Leaving the rye residue in the field up to and after soybean harvest offers benefits to soil.

“Leaving rye to grow until heading or beyond provides ground cover for winter,” says Ostlie. “This means that a single winter rye crop could provide cover for the winters prior to and after soybean production.”

Some varieties of rye are better than others at suppressing weeds. In the study, Hancock and ND Dylan varieties outperformed others. “We saw a drastic difference in these varieties in terms of their ability to control weeds,” says Ostlie.

Getting a good stand of rye is also critical to successful weed control, he adds.

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