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Improved soil health, weed control are among benefits of planting into living cover crops

THE TRACTOR AND PLANTER MAKE THEIR WAY through a waist-high jungle of cereal rye, depositing soybean seeds into the soil underneath the thick, green growth. It’s early June, and Adam Jones has yet to spray a single ounce of herbicide in this field on his Lewis County, Mo., farm.

“I did nothing from a weed-control standpoint during February, March, April, May and even the first part of June,” Jones said. “So, I ran almost four months with no soil residual herbicides there. Normally, I would have had to either work that field or spray it two or three times to get to June 3. That’s a big deal.”

Not that long ago, this would have seemed like a foolhardy move to many grow­ers, but “planting green” into cover crops is becoming more common on Midwest farms. Surveys by USDA indicate that more than half of cover crop producers have now adopted this practice in which the cash crop—typically soybeans or corn—is seeded directly into an actively growing cover crop instead of terminating it earlier in the season.

“As growers gain experience with cover crops, they’re becoming more comfort­able planting green, especially with soybeans into cereal rye,” said Jones, MFA’s natural resources conservation specialist. “By letting that cover crop mature and get as tall as possible before you terminate, you’re adding more plant material to that field. And the more plant material you add, the faster you will see results of using cover crops.”

While it may seem counter-intuitive to plant while there’s still another crop in the ground, this management technique can offer both soil health and logistical advantages. Of the cover crop producers surveyed in 2020 by USDA, 68% report­ed better soil moisture management when planting green, and more than half said it helped them plant earlier than they could in fields that didn’t have cover crops.

“When the cover crop is allowed to grow longer, it provides greater above- and below-ground biomass, which helps to increase water infiltration and reduce surface runoff and soil erosion,” Jones said. “Farmers can often plant sooner in the spring because the living cover crop helps keep the soil warmer and drier.”

In addition, 70% of the cover crop survey respondents said planting green improved their weed control. When actively growing, cover crops compete with weeds for light, nutrients and water, Jones explained, and then the terminated residue continues to physically suppress weeds by creating a barrier and blocking light from reaching the soil surface. Following up with recom­mended passes of residual herbicides will be needed later in the season, he added.

On his farm, Jones said he prefers to plant green and then terminate the cover crop within a few days, if conditions allow. Pulling the planter at an angle across the rows of rye helps knock back the cover crop until he can get it sprayed.

“I want that cover crop to go down and stay down once I plant, so it needs to be terminated fairly quickly,” he said. “If you give the rye a chance to stand back up, your soybeans will take a hit from losing sunlight. Also, you want that residue down on the ground as much as possible for weed control. I typically want to spray less than three or four days after planting. The only way I would plant into the cover crop and let it grow with the soybeans for a while is if I had an ability to roll it down—and there are a lot of farmers who successfully do that.”

In his experience, Jones said there have been no yield losses associated with the practice on his farm. In fact, he’s often seen slight yield increases compared to other fields where cover crops were terminated earlier in their growth stages. Industry data and grower surveys corroborate that observation.

“All the research will tell you there is not a yield penalty, which I believe to 100% be correct,” Jones said. “If anything, a lot of them will show a bushel or two yield bump. There’s a couple of reasons why. The cover crops are utilizing extra nitrate out of the soil profile, which forces the soybeans to work a little bit harder to fix their nitrogen. That’s a good thing. Also, the residue on the soil surface helps prevent those dry periods. Soybeans are not nearly as deeply rooted as cereal rye, so pre­serving that moisture in the upper part of the profile is pretty critical.”

Planting into living cover crops isn’t that much different from planting into other no-till or even conventionally tilled condi­tions, Jones added. Success largely depends on good seed-to-soil contact.

“Even with that much residue and biomass on top of the ground, the mechanics of planting are going to be the same,” he said. “We still need to open the slot. We still need to place the seed accurately, maintain it in the trench, and then close it back up correctly to get good germination and emergence.”

Planter setup is key to making sure those steps happen, ac­cording to Lucas Brass, soil conservationist with USDA Natural Resources Conservation Service in northeast Missouri. Both the planter and attachments need to be in good condition and properly adjusted, he said, accounting for the thickness of the standing cover and field conditions.

“When you go into rye or any type of thick cover, you have to get it out of the way,” Brass said. “You want to have good sharp openers that will cut through the cover and avoid pushing residue down into your seed trench. You also need a good seed firmer to make sure you’re getting that seed down in the bottom of the trench. The closing wheels are also important. There are lot of options out there. Make sure you have something that works in your fields.”

If growers have not tried planting green in the past, Jones recommends they start by seeding soybeans into cereal rye. Planting corn into a living cover crop is pos­sible, he said, but takes more advanced management.

“Typically, when planting green with corn, you want a much more balanced cover crop mix, something that is not as cereal grain dominated,” Jones explained. “It should have wheat or oats or something like that but also species with a lower carbon-to-nitrogen ratio such as winter peas, canola or crimson clover. You’re trying to balance the biomass on the ground so you don’t cannibalize all your nitrogen for the year. Planting soybeans into cereal rye works in most fields the first time you try it. With corn, it means a little more give and take.”

Planting green is an allowed practice under Risk Management Agency guidelines, Brass pointed out. Growers should check with their crop insurance agent or USDA office to make sure they are following the planting and termination parameters set for their areas.

Back on his family farm, Jones is gearing up for another season of planting green. Last year, he said about 80% of his soybeans were planted into standing rye. This year, he intends for that number to be 100%.

“Erosion control, weed sup­pression, moisture management, increased organic matter—the benefits of planting green definite­ly outweigh the concerns, as long as you’re doing everything right,” Jones said. “I have yet to see a downside. Don’t be afraid to try it.”

For more information on inte­grating cover crops into your crop production strategies, contact your local NRCS office or MFA affiliate or email Adam Jones at ajones@ mfa-inc.com.

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