May 21, 2024

Setting goals first step in cover cropping

Continuing to learn and adapt

Carl Joern

JOHNSTON, Iowa — What’s your goal with cover crops? That’s typically the first question an agronomist asks when a farmer is seeking advice on cover cropping decisions.

“There’s a litany of different answers that one could provide,” said Carl Joern, Pioneer field agronomist in Indiana.

“That’s the specific thing to have in mind because that often dictates species, seeding rates, etc.,” added Kevin Fry, Pioneer field agronomist in Pennsylvania.

Joern and Fry, along with Indiana field agronomists Brian Shrader and Ben Jacob, recently hosted a podcast detailing various cover crop topics.

One goal for using cover crops may be for forages.

“Farmers are taking off corn silage and then putting in some type of cereal rye. It’s usually either triticale, rye or wheat that they’ll then, in turn, chop off as forage in the spring and then go back to corn silage rotation,” Fry said.

Traditional cover crops are used for erosion control, particularly where soils and typography necessitate their use.

“We have a lot of slopes and primarily we’re trying to get some type of a cover on our soybean ground to reduce a lot of the winter washing,” Fry continued.

“When not having a lot of residue out there, even in our no-till soils, those soybean fields will wash out quite a bit. We’re limited in top soil to begin with and we want to hang on to everything we can.

“Forage and erosion control are probably the two primary reasons we’ve been using cover crops here.”

Nutrient recycling, keeping the nutrients in the soil and breaking up nutrient stratification are other factors in utilizing cover crops, Shrader noted.

“I think in many of the cases what we’re doing with the cereals especially in our livestock operations is scavenging that nitrogen and trying to hold it over for next year. We have manure applications going on in the fall or early in the spring when we don’t have a growing crop out there. That cereal crop can actually grab and hold a lot of that manure nitrogen and hopefully be plant available later in the summer,” Fry said.

“Also, a lot are using turnips and some of these annual rye grasses that have a deeper rooting system to try and break up some of that nutrient stratification, especially those long-term no-till systems.

“A lot of times, good earthworm activity and that overall improvement in soil health also helps with nutrient stratification.”

Weed suppression is touted as another benefit for utilizing cover crops.

“Cover crops do a heck of a good job at keeping the mare’s tail population down. Even as little as a half bushel an acre of cover crop seeded late can have an effect. It doesn’t have to be that thick of a cover crop to have that effect and keep mare’s tail under control,” Fry said.

“The longer you allow the cover crop to grow and the thicker and heavier that mulch is, that’s when that weed control aspect can carry over into controlling some of those stubborn summer annuals like water hemp.”

C/N Ratio

Joern said one of the biggest challenges with cover crop adoption and going into the next crop in the spring is overwintering cereal rye and the carbon-to-nitrogen ratio.

“As the cereal rye is decomposing that high carbon-to-nitrogen ratio, if folks are trying to go to corn that spring, do you have any experience where you’ve seen guys going from an overwintering rye to planting corn that spring? Is there a nitrogen application that you’re advocating for that’s different than what would otherwise be done? Or, is going from rye to corn just a bad idea,” he said.

“That is not an easy question. With the amount of nutrient application in most manure livestock operations we don’t necessarily run into that tie-up, so to speak, but in grain operations, absolutely. Especially where they let rye cover crop get big,” Fry answered.

“When that carbon-to-nitrogen ratio gets that tall, guys will put in an extra application of nitrogen to try to reduce the carbon-to-nitrogen ratio so they don’t have a nitrogen tie-up issue and the corn crop being short. That is something that’s very real. When exactly to do that, that’s a challenge. Is it boot high? Is it knee high? I think approximately in that range.

“A former Extension colleague of mine said as long as you can still see that rye residue in the field, that that nitrogen isn’t available for the plants. If the residue is breaking down by the end of the season, then that nitrogen has become available for the plants. That’s a rule of thumb that I’ll often use.”

There are also varying advantages and disadvantages in terms of cereal rye termination in the spring.

“A lot of guys are using cover crops for moisture management. We struggle with just drying soils in the spring and they’ll leave that cover crop out there to pull moisture out of the soil. A lot of times, they’ll plant green through that, terminate the cover crop later in the season, and then use that mulch and cover as a moisture conservation aspect when it gets dry to reduce evaporation,” Fry said.

“When we had our drought this year they were taking if off for forages and then no-tilling into that, that was some of the most challenging conditions where there was no moisture left in the soil profile by that time period. Then we got dry in June, that corn crop really suffered. It’s a difficult decision to make.”

Planting Green?

Fry was asked at what point is cereal rye too big to plant green or is that a misnomer and it can be as tall as the tractor tires.

“I continue to learn this whole planting green aspect, and from what I’ve learned and been experienced with is I don’t think it can get too big. I think in many cases, the bigger it is the easier it is to plant into. Where I’ve seen the best success with it is where guys are rolling that cover crop,” he said.

“We’ve always talked about allelopathy with cereal rye and corn, but in reality that mainly occurs when the cereal rye is still standing and the corn is trying to grow through a standing cover crop. Once you roll it and get it flat, the corn really seems to respond well and grows very well.

“Some of the anecdotal things that I’ve seen is when you have that living cover crop out there in the spring it almost gains you about a half a day time to get back in there and start planting a little sooner compared to those without cover crops in wet springs.

“The other thing to keep in mind is the seeding rate is very, very important. You don’t just want to throw a couple bushel of cover crop out there and expect to plant green into it because it can get very thick. A bushel is plenty.”


“My conventional wisdom that I always shared was if you’re going to terminate your cover crop ahead of planting, at least do it two weeks prior to planting,” Joern noted. “Is that something that you also subscribe to or is that antiquated at this point if a guy is looking to terminate ahead of planting?”

“These aren’t easy answers because we’ve talked about the moisture management aspect. In many cases, if we burn that rye cover crop down and then it gets wet again and we’ve got a dead cover crop it almost acts like a sponge and takes even longer to dry out,” Fry said.

“But in contrast, you’re also right about terminating two weeks ahead of planting. As I’ve been learning more about this cover crop — in fact it wasn’t long ago that I was in the same boat where I would want that cover crop brown and dead — it makes it easier to plant into when you spray it and it’s dead and dry two weeks prior to planting.

“It’s not an easy yes or no. I think we continue to learn and adapt and that’s where farmers are going to have to kind of ease their way into it. If you think about the equipment necessary to get in there and plant green, a great way to overcome that is to spray it so it’s dead and dry and easier to plant into with the equipment they have on hand and still be able to utilize the cover crop and the benefits of it.

“As we talk about some of the challenges of going from a cereal rye to a corn crop, soybeans respond very well to planting green into cover crops in general. That’s a great way to avoid some of the challenges with a corn crop is to use it in your soybean crop.”

Tom Doran

Tom C. Doran

Field Editor