By Sarah Hill, Associate Editor

Dealing with Downed CornMidwestern farmers may already have been thinking about seeding cover crops when the derecho hit earlier this month.

There are a number of flattened corn acres in Nebraska, Iowa, Illinois and Indiana, but still opportunities to get covers seeded yet this growing season, says Meaghan Anderson, Field Agronomist with Iowa State University Extension.

“In some cases, the canopy has opened up a bit — partially because of the storm,” says Anderson. “Because that corn is leaning over, more seed can reach the soil surface and get sunlight earlier than it normally would.”

The weather has been very hot in the Midwest the past few weeks, so the soil is primed for a rain. If that rain were to occur, Anderson says that a cover crop would respond quickly.

What to Do First

In an ideal situation, Anderson says, an insurance adjustor would release acres affected by the derecho soon so the unharvestable crop can be removed from the field.

“In some parts of Iowa, people are already destroying their crop,” she adds.

Destroying the crop can be done in several ways. Using a vertical-tillage tool or disc to chop up and resize residue are the two big ones, according to Anderson.

“Try to harvest what you can and process those stalks through the combine to break it up a little bit,” adds Tony Bailey, USDA NRCS State Conservation Agronomist for Indiana.

Dealing with Challenging Residue

Downed corn due to the derecho will definitely cause growers some challenges with seeding a cover crop, according to Anderson, because it will be harder to get the proper seed-to-soil contact for that cover crop seed.

“You’re looking at entire cornstalks that are 6-8 feet tall,” she says. “Those stalks are so carbon heavy, so lignified.”

Anderson says there are three key differences between the 2020 growing season and a normal growing year:

• Because the stalks are down, there are a lot more ears of corn and kernels on the ground, which are additional residue on the soil.

• The amount of plant vegetative tissue is the same, just in a different form, since it has not been chopped up yet.

• Because the corn is already down it’s already dying, so the degradation process has been jumpstarted. So, there may be an opportunity for more microbial degradation.

Species Options for Covers

Cover crops can play an important role in mitigating the effects of storm damage to a degree, says Bailey.

“If you want to take advantage of not being able to have a crop in the field, getting a cover crop established will help in the following crop year,” he says. “Cover crops build healthier soils and crops and help water and air move through the soil profile better. That can help next year’s crop be more resilient to weather events.”

The tried-and-true standby of cover crop species, cereal rye, is a safe bet because it’s easy to seed, fairly easy to grow, tolerate cold conditions and comes back in the spring, Anderson says.

“If it’s primarily used in fields going from corn to soybeans, we have an opportunity with cereal rye and its high level of biomass to get some weed suppression in the spring,” she says. “There are other options. If oats are seeded early, which can be done this year, and we get enough rain, would be a good option this year. Although oats are inexpensive, they also winterkill, which growers might want because there will be less residue to deal with in the spring.”

Other species that need more time and might not typically do as well when seeded after fall harvest, such as radish, are also up for consideration. Bailey agrees.

“Cereal rye ahead of soybeans has worked well,” he says. “We don’t have some of the issues with nitrogen immobilization that we see with the high carbon cereal rye. Using oats and/or radish, even if it winterkills, if used before corn, can still get the soil biology going.”

However, Anderson says that cover crop seed still needs to get good seed-to-soil contact and moisture in order to do well.

“There’s a value proposition with evaluating cover crop species. The seed costs more, and it’s a risky environment right now because the soil is dry,” she says. “If the rain doesn’t turn on pretty quickly, I wouldn’t take the risk of seeding something that’s going to cost more money and not come up.”

Bailey adds that this extreme weather event is most challenging for those growers who are just transitioning into using covers.

“For those growers transitioning to a high-residue planting system, such as no-till or strip-till, or who haven’t used cover crops in the past, they have a lot of residue on the surface for the first 3 years,” he says. “The soil biology isn’t ready for all that residue. Farmers are afraid they’re going to be buried in residue, and they’re right, to an extent, those first few years. This is where cover crops are really important to jump start the biology.”

Min-Till and Covers

“Ideally, growers could try to do any tillage and seed covers in one pass, so that light tillage can incorporate the seed into the soil,” Anderson says.

Bailey recommends adding a seeder box on any tillage equipment or using a drill to seed cover crops. He emphasizes that if tillage is being done, its primary purpose should be supporting the seeding of covers.

“If the primary purpose of tillage is just to be doing tillage, that’s usually done 2-4 inches deep or more, which is too deep for cover crop seed,” he says. “Having the primary purpose of tillage being to knock down and size the residue so the cover crop seed can get better seed-to-soil contact is a good way to think about it.”

“It also makes it a less expensive tillage pass, so you’re not using as much horsepower or fuel, while still getting the benefits of cover crops. Especially if the cover crop seed is expensive, you want to give it a good chance.”

Seeding cover crops at about ½-inch deep, depending on species and soil moisture, is the depth Bailey recommends. If a grower has never used covers before, there are some important considerations.

“If the soil lacks biology, then you need to do as little tillage as possible,” Bailey says. “Look at the whole field. Does the whole field need to be done or just part of it?”

Bailey also discourages growers from doing “revenge tillage,” as tempting as it may be.

“After any bad weather event, or the crop is down and people are mad at the year and the crop. But let’s not make it worse by doing a lot of tillage,” he says. “Let’s do the bare minimum of what we need to do if any.”

Too much tillage or sizing of residue can result in residue floating or blowing away to settle in other parts of the field, which may end up needing more tillage to spread it out ahead of the next planting period.           

It can also be tempting to use tillage to prepare the seedbed in the fall, but Bailey warns against it.

“It doesn’t matter if you have a perfect seedbed in the fall,” he says. “That ensures you’ll have crusting, probably erosion and runoff, all of which can be problematic over the winter. It also guarantees you’ll have at least one more tillage pass in the spring.”

Add Cattle to the System

Another consideration for dealing with downed corn that Bailey recommends is putting cattle on it to graze and harvest the corn—whether they belong to the grower or a neighbor.

“That adds another piece to the biology and helps it along,” he says. “Of course, this scenario works best if the fencing and water infrastructure are already present or easily added.”

Bailey also cautions that if fields are too wet, cattle can cause soil compaction.