Weed FREE! An ode to rye
Minnesota researcher Paul Porter is working with five farmers to figure out the best way to use a rye cover crop as an effective weed suppressant for soybeans. No-till planting in rye is looking really strong as a strategy.

By Deborah A. Hyk


Research at a Glance

Rye and Soybeans, Minnesota

Summary: Using rye cover crop as a weed suppressant for soybeans

Researcher: Paul Porter, agronomist at the University of Minnesota.

Farm: Robin Brekken, MN farmer with 3,000 acres of organic soybeans.

Outcome: In progress
1st year of study, 4th year of planting soybeans into rye for Brekken. Brekken personal trials have found: It boosts yield, fields are cleaner and the process is less expensive

SEPTEMBER 12, 2003: If there existed, somewhere in the known universe, a highly effective organic weed control, organic producers everywhere would be singing its praises and lining up for their share. Though a silver bullet does not exist, hope remains for improved weed control. Researchers and inventive farmers continue their search for rotations and intermingling planting methods that take on weedy fields and return meaty yields.

One of the Cinderellas of this story could be rye, currently under investigation in Minnesota as a companion for soybeans to curb weed growth. Paul Porter, agronomist at the University of Minnesota, is working with five farmers to determine the methodology for, and efficacy of, planting soybeans in fields that were sown with rye the previous fall.

This study is benefiting from the experience and knowledge of Robin Brekken, a farmer from Crookston, Minnesota, who began transitioning to organic in 1998. Although this is only the first year of the study, it is Brekken’s fourth year of planting soybeans into rye. History has shown him that rye holds promise. Each year has presented slightly different challenges for Brekken, and this year has been no different. Yet Brekken’s time spent with rye may help provide a fine-tuned recommendation for future use of rye as a weed suppressant. With 3,000 acres to tend to, he’s on a quest for something efficient and effective.

Flaming can be a very effective weed control, Brekken says, provided a farmer can get into the field. But this spring, wet weather plagued parts of Minnesota and kept equipment and farmers out of fields.

In this setting, Brekken finds the rye alternative attractive. It can provide a potent mixture of allelopathy and shade for the soil, inhibiting weed seed germination. Soybean seeds are large enough to germinate and flourish amidst a stand of rye. The key is getting the rye established in fall, prior to next spring’s soybean crop. Brekken has learned that this requires a bit of finesse.

Learning to capitalize on the many benefits of rye

To help farmers develop the right plans—timing, varieties and methods—for using rye, Porter wrote a grant, which was awarded by the Minnesota Department of Agriculture. The grant is part of a project supporting efforts aimed at increasing knowledge about sustainable agriculture and energy sources.

The idea for the grant came to Porter from farmer folklore in Minnesota: The saying goes that soybeans are made in August. Porter theorized that with the use of rye, a farm could more easily capitalize on the most productive time of year for soybeans. The rye could help diminish weeds and retain moisture earlier in the season, nurturing a good stand of beans. Then, with good weather, the crop would be a good one.

The grant is looking at using rye in both conventional and organic production systems. Farmers routinely use herbicides to control weeds in soybeans, and Porter notes that some of these have a negative effect on the soybeans. His hope is that rye would make this process easier on the soybeans by providing more effective weed control.

Finding candidates willing to participate in the study was not too difficult. “Some farmers were already using rye,” says Porter. They were in the midst of determining the optimal seeding rate and planting date.

Robin Brekken of Crookston, Minnesota notes, “If we can get the beans planted and the rye eliminated, for the most part we are basically done for the year.” The simplicity of the soybeans planted into rye is what attracted him to this weed control method.

Porter also hoped he could take the weed control notion one step further, turning it into a best management practice for other reasons. Rye appears to improve environmental conditions all around the field, says Porter. The fall-planted rye crop is a valuable asset in controlling runoff and nutrient leaching. The rye plants capture and hold nutrients and moisture in place, reducing the amount that reaches rivers, streams and ground water.

In much of Minnesota, there is often excess water in the soil at certain times of the year. For example, notes Porter, “in the fall, these areas often get a soil moisture recharge in the form of rain.” Then in spring, heavy rains cause runoff through the soil into both surface and subsurface drainage tiles.

Initially, Porter conducted research in southwest Minnesota to determine what would happen if rye were seeded after corn. He and his colleagues documented that runoff was substantially reduced. Rye doesn’t halt all erosion, but it can reduce it, along with the amount of nitrogen in runoff water.

It was then that farmers like Brekken caught Porter’s attention. Brekken, along with other organic and conventional growers in the state, was planting rye in the fall, ahead of soybeans that would be planted later in the spring. Porter hoped to devise a system for both organic and conventional farmers to use as a cover crop.

Robin Brekken’s 4-year relationship with rye:
he’s still learning

As with many aspects of farming, planting soybeans into rye is still a process under development. Brekken is no stranger to the practice, but he has not perfected it yet. Before entering the study, Brekken had his first experience with rye for weed control in the fall of 1999. He had begun his transition to organic production at this point, though he wasn’t fully certified as organic until the spring of 2001. His plan then was to solid seed the soybeans with a Case IH SDX planter—using a drilling method. At this point, he was planting soybeans at a ratio of 120 lb per acre—double seeding. Almost immediately, he discovered some of the challenges of the method.

YEAR ONE: That year, he tilled the rye when it reached about 8” to 10” tall. This was done prior to drilling soybeans in the spring. This approach did not provide an ideal seedbed, he notes. “The root mass of rye is incredible—softball sized,” he added. To deal with this, the fields were tilled again before the beans were planted. Then, says Brekken, he prayed for rain.
Rain was abundant; so were weeds. Brekken had 100 migrant workers ready to help him pull weeds if needed. He also planned to run several different harrows through the fields. The skies never cleared for long enough to provide the workers adequate time in the fields. Eventually, Brekken sent everyone home. Yields were acceptable that year, but Brekken had his doubts about tilling the next spring. He would not give up on rye just yet.

YEAR TWO: Hoping to further refine this method, Brekken decided to try something different in the spring of 2001. He decided to till again, but left a 40’-wide strip of untilled rye. After the rye headed—which was roughly two weeks after the soybeans were planted--this strip was shredded with an Alloway shredder. He planted the soybeans amidst the rye. Immediately, he noticed that the soil was different in the two areas. Moisture was abundant in the soil under the rye. Brekken says he could have planted the soybeans ½“ deep. “In the tilled area, we would have planted 4 inches deep just to reach some moisture,” he notes.


As the plants matured side by side, it was easy to see something unique about those in the shredded rye, Brekken recalls. He noticed early on that these plants were shorter, and a lighter green in color. In the tilled area, the plants were taller, with bigger leaves that were a darker green.

Porter is unsure at this point why the color would vary in the two fields. “Soybeans produce their own nitrogen, so that’s not a concern,” he notes. Whatever the rye is taking away from the soybeans is yet to be studied. Porter notes that the first issue is weed control. Later studies will determine nutrient management.

Regardless, the color variation and plant size caught Brekken’s attention. So he took a closer look. He counted the number of nodes that would eventually become bean-bearing pods on plants in both the mowed area and the tilled area. Plants in the two different settings were bearing identical numbers of pods.
Later, he found that count to be only the first chapter in a story full of twists and turns. Despite the less-vibrant color of the soybeans in the mowed rye, those plants produced two- and three-bean pods. In the tilled area, plants were yielding one- and two-bean pods.

“That was when the light went on,” says Brekken. Eventually, the harvest bore out what this pod count foretold. “They were nicest beans I had,” he says.

The forty-foot strip yielded about 35/bu acre. Where he had tilled out the rye, the yield was 28.5/bu. Before transitioning to organic production, Brekken would routinely harvest 35-38/bu. per acre. At harvest time, he ran his combine through the shredded rye strip, and weighed the beans. Then he repeated the process in the tilled rye. He discovered that the soybeans in the mowed rye provided an eventual 6.66 bushes more per acre than the soy where he had tilled the rye.

YEAR THREE: The result was surprising to Brekken, and promising. During the next year, with rye planted in September of 2001, and soybeans in spring 2002, he decided to jump to 1500 acres of soybeans, all interplanted into rye that was shredded two weeks after planting the soybeans. “I thought it was ironic,” he says. “For less yield, we made two tillage passes with the cultivator, and we had planned to make even more passes with the harrow and had migrant workers in the field.”

In addition, tilling dried out the field. Where rye is mowed, rain is far less critical because the rye helps retain the moisture in the soil. However, moisture is still critical, because the rye itself uses a great deal of moisture. Brekken notes that if the area ever had a dry spring, the rye may steal too much moisture from soybeans, preventing germination. So far, things looked good for the rye: It boosts yield, fields are cleaner and the process is less expensive.

In the fall, the harvest ranged from just 9 bu./acre to 35 bu./acre. In the areas where the soybeans yield was lower, the seeds and plants had been washed out by heavy early season rains. Yet weed control was adequate, and Brekken felt he had found an approach that, given more ideal weather, could work.

Having spent many years as a conventional farm, Brekken can easily contrast rye with herbicides for weed control. “There’s no guarantee that they’ll work,” he says of the herbicides. Rye is cheaper than chemicals, to boot. An acre of rye seed runs about $8; herbicides can run from $15 to $25/acre. He also senses that planting rye will reduce the amount of labor involved in raising soybeans organically versus conventional methods of production. What’s more, he can also sell the rye produced in the field by having the product seined, separating the soybeans from the re-emerged rye.

YEAR FOUR: As is always the case in farming, Brekken faced another, new challenge with his rye this year. Last fall was wet, and the rye was planted later than would be an ideal time. (Ideally, in Minnesota, rye is planted the last week in August or the first week in September.) As a result, more weeds popped up this year in the rye because it was behind schedule when compared with past years.

Porter had already noted that rye planted later in the fall provides reduced coverage, and reduced weed suppression. “In the case of last fall, Mother Nature set the planting date,” notes Brekken, so there was nothing he could do about it. Yet he recognizes that this practice is a work in progress, and his optimism shows: Initially, Brekken thought that this situation may provide him with a learning experience, and perhaps also with an even simpler way of killing off the rye and keeping the weeds in check.

Brekken discussed the weed situation with Porter to determine some method of dealing with it before planting the soybeans. The two decided that Brekken should run a harrow through the fields. He did this two times, and in some cases three times, through many of the fields. Some fields were left because the rye was well established and had successfully suppressed the weeds.


To knock down the weeds, Brekken used a Brandt harrow, which produces about four to five inches of tillage. The tooth is large—9/16 inches by 28 inches. This harrow allows the farmer to tip it hydraulically, and requires a 300 horsepower tractor just to pull it. “It can be very aggressive,” notes Brekken.

Back in 2001, Brekken had noticed that the areas where he accidentally made two passes when drilling the beans were exceptionally productive. So this year, Brekken intentionally double seeded his entire soy crop in this manner. He “solid seeded” the soybeans by crossing the fields a second time at a 90 degree angle to the first pass with the soybean driller. Each acre was planted with 180 lb.—90 lb. in one direction, and another 90 lb. planted at a right angle to the first 90 lb. “This is the first year we cross-seeded, using a no till drill. The disks on the drill cut up the rye,” says Brekken. This managed to set back and kill enough rye that he did not need to actually use a shredder this year.

This year thus far has been a mixture of weather that has been at extremes. The spring was quite wet, and early summer proved no different. “Earlier in the year, we experienced a rainfall of four inches in one hour,” says Brekken.

Then, the dry weather set up, with the last measurable rain falling in the last week in July. Brekken can see that the plants are sloughing pods at the tops of the plants, and lower down are sloughing beans within the pods. “If I had to guess, I’d say I’m going to get two-thirds of what I could have harvested. This year would have been the nicest beans I’d ever had,” he notes.

Knowing the role the weather plays, as all farmers do, Brekken sees the rye/soy method as one that he could perhaps bank on. Today, on September 5, he’s planting rye. He’s not giving up on it yet. He knows that he’s in the process of learning. With the curve balls that the weather throws at him, like every farmer, he’s willing to take a swing. He never knows when he may hit a double—or a home run.

Looking to the future: Benefits for both organic and conventional growers

Porter, too, is optimistic about the project, even though it is only in the earliest stages. “What I like is that we’re trying to make the process work in the conventional world,” he says. Even in conventional production, rye sucks up and hangs on to moisture, keeping it available for soybeans. It can provide a no-till method that farmers using the approach may appreciate. In drier areas, tilling exposes the soil, allowing precious moisture to evaporate. (For future study, Porter has recommended that his on-farm collaborators use two varieties of rye, planted in different fields. These will be evaluated to select the better of the two for future use.)

Wildlife cover is another benefit. “On one farm, we kicked up a hen mallard nesting in the rye,” notes Porter. The rye also provides habitat and feed for deer and geese in the fall and in spring.

Brekken says he’s not married to rye, but he knows it has benefits that he’s not sure he can find elsewhere. “If we can plant and be done, that’s unheard of,” he says. “But that’s a possibility—we’ve done that with rye.” In addition, this system gives him the ability to not worry about weather. After years of conventional farming, Brekken is married to organic production of food-grade soybeans. “It’s the greatest thing: I’m growing something that people want to buy—versus going to elevator asking what they’re going to give me for it.”