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Seeding soybeans into rye

Green growth in spring helps to manage excess moisture, provides early-season protection from soil erosion, and also suppresses weeds

Grain farmers across Western Canada are showing interest in cover crops, but few have taken the step, as many North Dakota farmers have, of green-seeding soybeans in the spring into a fall rye cover crop.

“The context of green seeding is to push that shoulder season fallow period out of the rotation by using annuals or winter annuals to continuously have living plants, then direct seeding into the living green cover and terminating it to enable the crop just planted to grow,” says Yvonne Lawley, associate professor of agronomy and cropping systems at the University of Manitoba.

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Fall rye and soybeans seem to be the go-to combination for many farmers trying green seeding. Lawley says there are a few good reasons.

“Fall rye is a reliable crop that will overwinter for us. One of the issues with overwintering cover crops is that you don’t know what is going to happen with N as that living cover crop dies. Microbes need to break down that material and they are going to be scavenging for N and if you are trying to get a crop that needs a lot of N early up and out of the ground, you can see immobilization of any N that was in the soil and/or fertilizer N that you are applying, depending upon placement and how hungry those microbes are.”

North Dakota farmers are also using a cereal rye cover crop because of resistant weed problems, says Abbey Wick, assistant professor and extension soil health specialist at North Dakota State University (NDSU).

“It’s one more mode of action for controlling those weeds in the spring because cereal rye is so competitive with them. It doesn’t reduce the number of weeds, but it keeps them smaller, so when farmers are terminating the rye with a herbicide pass, they also kill the weeds that have established while they are still small.”

Wick’s research has shown that weed biomass in spring in fields with a rye cover crop can be up to 10 times lower than in a field with no cover crop.

Farmers in Western Canada wanting to try green seeding with fall rye can take a few tips from North Dakota farmers who have similar rotations. “Farther north, where we grow more wheat, farmers have to be cautious to ensure they don’t contaminate their wheat crops with cereal rye. So, there are some things the northern farmers are doing differently to the southern farmers just because of their rotations,” Wick says.

For instance, a four-year rotation allows farmers to plant fall rye two years away from a wheat crop to try and minimize the risk of contamination. Wick says some farmers don’t seed rye for the two final seeding passes at the edges of the field to ensure when they come in with their herbicide pass to terminate the rye, they don’t have to overshoot to make sure they get everything.

Dabbling with green seeding

Ryan Boyd of SG&R Farm Inc. near Forrest, Man., planted soybeans into a fall rye cover crop two years ago and says he’d do it every time if he had the choice.

Boyd seeded the fall rye on 120 acres after a pea crop, then planted soybeans early the following June. Although he did graze the rye for a couple of weeks before seeding the soybeans, he said it wouldn’t have been necessary.

“The rye had all headed out, and then I sprayed it and seeded the soybeans the same day,” Boyd says. “We have a disc drill, so we didn’t need to graze it but it was just a little bit of a bonus that we were able to do that.”

Boyd inoculated the soybeans as he normally would and the only other added fertility was a small amount of phosphate with the rye when he seeded it in the fall. The rye didn’t hurt soybean yield — Boyd achieved 40 bu./ac., which is average for his farm, plus the benefit of a little extra grazing for his cattle.

Multiple benefits

Seeding into fall rye can provide many benefits such as green growth in spring to manage excess moisture, early-season protection from soil erosion and helping to suppress weeds.

Those are the main benefits that Boyd noticed too.

“There was some residue so we didn’t have that bare field to blow all spring and dry out,” he says. “The rye choked out the weeds so it was pretty clean. I did spray it in-crop but I was debating about whether I had to or not.”

Wick says an important consideration with any cover crop is to determine the goal the farmer wants to achieve. That will help determine things such as seeding rates, species and the following crop. For example, rye could be a weed control strategy in problem areas such as saline spots.

If farmers use fall rye as a cover crop, they are committing to the next crop in the rotation, which must be compatible.

“They lose some flexibility because they can’t grow wheat,” Wick says. “They need to make sure that they know where the rye is and don’t make a mistake and plant a crop that isn’t compatible, and should be confident that they are going to plant soybeans.”

When to terminate

When to terminate the cover crop is a key management decision, and the University of Manitoba recently began a research project to compare the effects of different termination dates. Lawley and graduate student Virginia Janzen planted soybeans and edible beans into fall rye that was terminated two weeks before planting, a few days before, a few days after and two weeks after.

Wick says that decision, which often revolves around moisture, starts with making sure farmers keep an eye on the crop.

“They can’t just plant rye and forget it,” she says. “When rye starts growing in the spring it uses a lot of moisture, so they need to watch it to ensure the seedbed doesn’t dry out, and they keep some moisture there so that they can get a good stand. I have seen incidents where the seedbed dried out, and there’s no rain, and the soybean can be an entire growth stage behind, which we can’t afford in northern areas.”

Nick Cowan and his family, who manage 10,000 grain acres, 600 cows and a 1,500-head feedlot near Hartney, Man., has been green-seeding soybeans into a rye cover crop for three years. He bases his decision to terminate the rye on moisture.

“We sow our Roundup Ready soy- beans and then spray two passes of Roundup after we’ve seeded it,” he says. “If it’s a really wet spring we don’t take out the rye until the soybeans are up, just for moisture reasons, and if it’s dry, we take out the rye right away. It works really well for sucking up all the N out of the soil, so you get good nodulation of your soybeans and then the rye breaks down for a late-season boost.”

Cowan has a slightly different strategy for green seeding. He direct-seeds soybeans using his disc or shank drill in the spring into a fall cover crop of fall rye (seeded at 40 lbs./ac.), oats (20 lbs./ ac.) and barley (25 lbs./ac.), which he first grazes in October. The fall grazing pass ensures the rye regrowth isn’t too high to seed into the following spring, and the cover crop improves infiltration of any moisture.

Improving trafficability

Green seeding also improves trafficability and timing and ease of seeding.

“It seems counterintuitive to think you can plant more easily into a big biomass of green cover,” Lawley says. “But one of the reasons that farmers are interested in seeding into living residue instead of terminated residue from cover crops is that disc seeders in particular work better when the biomass is upright and still green compared to terminating it ahead of time, so it’s brown, decomposing and hold- ing moisture, which makes it harder to cut through.”

“Every time you lift up the shanks at the end of the field and turn around there’s not even a speck of dirt on them, so the cover crop keeps the seeder clean,” Cowan says “It can rain an inch and we can be seeding the next day.”

This article originally appeared in the October 2019 issue of the Soybean Guide.

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