Addressing the conundrum of planting into cover crops

Though the acreage of cover crops in Ohio has expanded dramatically in recent years due to their wide array of benefits, cover crop management presents annual conundrums about spring planting.

Should the cover crop be terminated prior to planting corn and soybeans or after? The standard answer for pretty much all things agricultural applies: it depends.

Glenn Harsh, who farms in Delaware County and has worked with cover crops for many years, said there are many factors to consider in this decision.

“The better way to do it is to plant green. There are certainly benefits because the cover crops get bigger and you get more biomass. If you have legumes out there they can fix more nitrogen. It also helps to dry out the soil. The plants are growing and taking up water and storing it for you. We find the

Glenn Harsh, Delaware County
Glenn Harsh, Delaware County

soil is dryer when you plant green than if you kill it a couple of weeks ahead,” Harsh said. “There are challenges though. If you can’t get it sprayed and planted, it gets big and rank and hard to kill. It all depends on the field and the weather and the type of cover crop.”

It also depends on the type of crop being planted. Soybeans, in general, are easier to manage when planting into cover crops, Harsh said. Because of this, Harsh is more liberal with the cover crop blends he uses heading into soybeans for his Glenndale Farms.

“Soybeans are much easier, so we are putting more emphasis on corn ground going to beans for a robust mix of cereal rye, annual rye, tillage radish, clover, and a little rape seed. That is the year we really try to build up the biomass. The nitrogen from the clover feeds the grass and the other plants in the spring. And it is the one time we can really do some good with the tillage radish,” he said. “Going from corn to beans we use Highboy broadcast seeding in late August through the corn. Our tracks line up with our sprayer tracks so it doesn’t cause too much crop damage.”

On the fields going into soybeans, Harsh uses per acre:

• 4 pounds annual rye

• 2 pounds crimson clover

• 3 pounds tillage radish (need to use a good radish)

• 1 pound rape seed,

• 25 pounds cereal rye.

This aggressive combination of cover crops costs $18 per acre and can accomplish quite a bit in a short time.

“The cereal rye offers more growth — it grows taller and grows later into the season. The annual rye is more like lawn grass with not as much biomass but it has a really good fibrous root system under it and it doesn’t get as tall as cereal rye in the spring,” Harsh said. “Clover is a legume to get some nitrogen and it competes with the other covers pretty well. It gets up above the annual rye and it looks nice in the field. It feeds nitrogen to the cover crops and the beans. The tillage radish breaks up hardpan. Rape gets a carrot-like root on it and it does a nice job breaking up the soil too and it gets some above-ground growth with nice yellow flowers.”

The way a field looks may seem unimportant, but Harsh said it may matter to landlords.

“The aesthetics of the cover crops are another plus.  Landlords enjoy the spring flowers. One of the landlords uses the crimson clover for flower arrangements,” he said. “It looks nice for the community too and that type of thing doesn’t hurt.”

By seeding in late August, Harsh hopes for 3 to 4 inches of cover crop growth by the time the corn is harvested.

“It helps support the machine traffic in the fall, especially when you get into wet weather. You don’t do as much damage to the fields and the plants are taking up water to dry the fields,” he said. “The radishes winter kill. The rape can die too but we have pretty good luck with it overwintering. It is only $1 per acre and you get a nice taproot. Last fall it didn’t grow as much as I’d have liked. We can get cereal rye growing into late November sometimes. We want to get it established so it will grow the next spring.”

The fields going into soybeans are sprayed with Roundup, 2,4-D and residual herbicide 7 to 10 days before planting.

“The cover crop is still green when we plant. The concern is that we get wet and the sprayed cover crop stops pulling up water and then it forms a mat. To alleviate this problem we spray some of our soybean acres and then plant and see what the weather will do. If needed, I’ll take out the 2,4-D and spray closer to when I’m going to plant. You have to be flexible with the spray program. It helps you get the most growth out of your cover crops and it works well for the soybeans,” Harsh said. “Sometimes we hit it with a Turbo-Till to break up that mat and get some dirt on top. You have to get a stand up but after that the mat is a good thing. The mat suppresses weeds, keeps soil temperatures lower and helps keep moisture in the field. We then post- spray. If there is something you didn’t get 100% killed you may have to adjust your post- to take care of that. We have not had trouble with covers escaping our post- program.

The soybeans are planted at variable rates from 160,000 to 185,000 for populations.

“You want to make sure your bean planter or drill is in good shape and you’re getting seed to soil contact. I encourage using fungicide insecticide and inoculant seed treatment. You can get into situations where you get more insects and pest pressure and the inoculant can help start nodulation as soon as possible,” he said. “You need proper adjustment of the planter. If you have row cleaners make sure they’re not wrapping.”

Because corn is less forgiving than soybeans, Harsh goes with a less aggressive cover crop blend before corn.

“When it is going to corn we go with more of a maintenance cover crop. I want enough roots out there to feed the earthworms and microbes but more biomass carries more risk and challenges. I use lower rates of annual rye, oats and some rape seed and maybe a little clover in front of corn,” Harsh said. “We plant it with a Turbo-Seeder or drill. We also apply, two tons of poultry manure per acre right behind the combine at soybean harvest.”

Before corn through the first week of October Harsh plants per acre:

• 10 pounds oats

• 4 pounds annual rye

• 2.5 pounds crimson clover

• 1.5 pounds rape.

This mix costs around $11 per acre. After the first week of October Harsh removes the clover from the blend. After Halloween he uses only 3 pounds annual ryegrass and a pound of rape.

“That way I am putting something out there and it costs about $4 to $5 an acre,” Harsh said. “I want to feed the microbes but keep cover crop costs low as the risk of cover crop stand establishment increases.”

Getting corn planted is then the top spring priority.

“For planting corn into cover crops there are two methods. One is to plant green, which means a spray two days before planting to five days after planting. The other is to spray two weeks prior to planting,” Harsh said. “We plant our first group of farms green. The fields that we plant green are in better condition because the cover crops dry the soil and make for better planting conditions. We start spraying corn fields two days before we start planting corn. We spray enough acres to plant corn for three to five days. We then start planting corn and plant for two days. At that time we again look at the forecast if the forecast indicates good planting for another three to five days we will spray off enough acres for three to five additional days of planting. If the forecast indicates heavy rains or an extended period of rain we will spray the majority of our corn acres. This prevents the covers from getting too large to easily manage.

“We take what we can get. There is no set formula. That is what makes cover crops tougher. You have to work with the weather conditions, growing conditions for the cover crops and what the weather gives you. It adds another level of management to planting in the spring. There is some art that goes with the science.”

The key is to not have the cover crop dying right as the corn is emerging.

“That is the tricky part. There are two things that happen in the five- to 10-day window after spraying. There are concerns about toxicity of the decaying cover crops, particularly between cereal rye, and the growing corn plant, so you don’t want to plant a week after spraying usually,” Harsh said. “You also don’t want nitrogen tied up in the plant carbon while the plants are dying and the microbes are eating it — it takes N to feed the microbes eating the carbon. The amount of carbon out there makes a difference with the carbon nitrogen ratio. There is a short-term N deficiency caused by the microbes feeding on the decomposing cover crops. After 10 days or so you get the microbes switching from consuming the carbon and not using so much N, making it more available for the young corn plant when it needs it.”

And, as with anyone planting corn, the calendar and the soil temperatures should be considered when planting into cover crops.

“We start planting about as early as anyone around here,” Harsh said. “It does depend on soil temperature. You also need to look at the heat unit forecast. If soil temperature is up and the forecast for warm temperatures is looking up, at the end of April we’ll start planting.”

Harsh plants corn at 2 to 3 inches deep, which also helps prevent issues with toxicity from the decaying cover crops.

“Make sure your planter is in excellent shape. You are presenting yourself with more challenges. Your down pressure is very important to get the seed at the depth you want without sidewall compaction. Your closing wheels are very important. You want to close the slot without smashing the seeds in there,” he said. “You need your row cleaners moving the residue but not making a trench.”

Nitrogen is also very important.

“Make sure you have 30 to 50 pounds of N available, particularly as 2-by-2 starter. You are better to stay away from broadcasting 28% because it can get tied up on the leaves of the cover crop. Then when you come back with a sidedress in your high residue situation get the nitrogen into the ground or at the roots with the Y-drops,” Harsh said. “If you are using cereal rye — which is not my preference — there has been work using rollers to flatten it that can kill it. It allows the coulters to slice through it more easily. I am going to try it but I have not worked with it yet. I have heard about good results with rollers.”

Of course, the worst-case scenario is a runaway cover crop.

“One of the biggest challenges is if the cover crops get away from you and you can’t get in to plant and the cover crop reaches maturity,” Harsh said. “Keeping cover crop seeding rates low helps with that, especially before corn.”

Typically, all of his acres going to soybeans get planted to a cover crop and Harsh tries to get most of the ground going to corn covered because of the many benefits.

“There is some magic in this whole thing. You can’t just have a set program. It is field-by-field management when planting cover crops that changes by the season and by the day. You have to be willing to do that management to use it on a large percentage of your acres. Spring planting with cover crops carries the most risk in yields. That is the scariest, riskiest part. Start small and work up,” Harsh said. “But building the soil to a healthier state makes it worth it. We have seen payoff in better water infiltration and more water holding capacity and getting rid of water during major rain events. Once you get through these hurdles you get stability with better soil health and the residue out there. Those are big positives that pay dividends economically.”

In addition to those benefits, cover crops set Glenndale Farms up for a better future.

“With the environment we are facing with nutrient management in the state of Ohio, anything we can do to keep nutrients and the soil on the land while increasing uptake efficiency are practices we need to be working toward,” Harsh said. “The more of us that can figure out how to make it work on acres across the state, the better off we are going to be. It takes a program approach of balancing this together. With cover crops you get fungi and microbes working in the soil to feed the plants. There is more going on in our soils than we know about.”






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One comment

  1. Great Article Matt, thanks for providing timely information related to the planter down pressure, seeding timeframes and terminations when using cover crops!

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