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Crops upon crops: Cover crops after corn silage

Heidi Johnson for Progressive Forage Published on 13 July 2017
Barley was aerially seeded into standing silage

Corn silage acres, left with limited crop residue and typically receiving a manure application after harvest, are ideal fields for cover crops.

Cover crops will help to hold manure and soil in place while improving soil health by keeping living roots in the soil for more months of the year.

Cover crops should be selected based on a farmer’s goals. Examples of goals might be erosion control, growing nitrogen, producing an alternative forage or increasing organic matter.

Typically, erosion control is one of the primary goals for using cover crops, but this can also be combined with other goals. It is also vitally important to choose the right cover crop for your location, rotation and equipment constraints.

Options

In the dairy country of the Upper Midwest, we don’t have a lot of growing season left after corn silage harvest, so our location greatly limits cover crop choices at that time of year. Small grains like cereal rye, oats, spring barley, wheat and triticale are really the best options for this region. Brassicas like radishes or rapeseed can work with a very early corn silage harvest.

However, in most years, we don’t get enough growing degree days after silage harvest for brassicas to grow big enough to provide adequate winter or spring residue cover. Likewise, the legume cover crops (various clovers, peas and vetches) don’t have enough time to nodulate at this time of year, so nitrogen production is little to none.

Legumes also typically have brittle residue, so it breaks down quickly and does not provide enough cover to protect the soil through the winter and spring.

Spring barley and oats are great options if planted early enough in the fall to produce enough growth to cover the soil with residue through winter and spring. In southern Wisconsin, we generally recommend barley and oats be planted by around mid-September to produce adequate biomass.

Cereal rye, winter wheat and triticale are really the only choices for late fall in the colder regions of the country. Rye is by far the most winter hardy of the three and is the best choice for very late planting dates. All three will survive most U.S. winters, so farmers will need to plan on managing these cover crops the following spring with an herbicide ahead of planting their cash crop.

Spring forage

For farmers who would like to use a cover crop as a spring forage, triticale and rye are the best choices. Triticale is harvested a bit later than rye, so it maintains forage quality for longer in the spring than rye. Letting rye or triticale grow long enough into the spring to take a forage cut will inevitably push back the planting date of the next crop and potentially impact yield, so farmers need to plan accordingly.

Barley residue is shown in the spring after the field a fall low-disturbance manure injectionIn Wisconsin, most dairy farmers who grow triticale and rye as a forage use it as heifer feed. But if it is harvested at the right time and gets put up well, it can also be fed to lactating animals.

Annual ryegrass is widely used as a cover crop in many parts of the U.S. and will grow adequately in the fall after silage harvest. However, annual ryegrass has shown a propensity to develop herbicide resistance in certain regions, and many weed scientists caution against its use.

Those on the other side of the debate claim it is manageable with the appropriate herbicide program. If a farmer chooses to use annual ryegrass as a cover crop, they should investigate the best herbicide, rate and timing to ensure timely spring termination.

Rotation considerations

Farmers also need to consider their planned crop rotation when they pick a cover crop so the cover crop doesn’t interfere with the next season’s cash crop planting and management. There are certain cash crops that seem to fare better after cover crops than others.

For example, many farmers across the region report stunted or yellow corn after a cereal rye cover crop. Researchers have cited many possible reasons for this: nitrogen deficiency, an increase in seedling diseases and allelopathy, to name a few. It is likely some combination of these. This stunting doesn’t always result in a yield deficit, but it has made many farmers nervous.

A rye cover crop can also increase the incidence of corn pests such as cutworm and armyworm. This should not discourage farmers from trying this, but they should seek the counsel of experienced cover croppers in their region to learn management tips for avoiding these issues.

Planting options

Farmers should also be prepared to make sure the planter is set up for success with cover crops. They should be prepared to experiment a bit with down pressure, residue management and possibly different closing wheels to optimize their setup for a particular situation.

Heavy cover crop residue can lead to poor seed slot closure or seed depth if the settings are off. You can talk to 10 experienced cover croppers and get 10 different suggestions for planter setup, so every farmer needs to work by trial and error and sift through the recommendations to find what works for their fields and crops.

After a cover crop is selected, a farmer then needs to decide how they will plant it. Drilling, air flow seeding, spinner seeding and airplane (or helicopter) seeding are all possible.

Farmers will have to choose a planting method based on availability and price, but they should also try to find a planting method which allows them to get the cover planted as early as possible. The goal is to get as much growth as possible before winter.

Airplanes and high-boys allow planting a cover crop into a standing cash crop. Cover crops should not be seeded more than two to three weeks prior to silage harvest, or the cover crop seedlings will become shaded and die in the understory. Drilling or broadcast seeding are options after harvest.

Drilled cover crops will germinate more quickly and typically accumulate more biomass by the end of the season than broadcast seed. Broadcast cover crop seed is also vulnerable to slugs – an up-and-coming pest in reduced-tillage systems. Slugs will eat the germ end off of many cover crop seeds, not allowing them to germinate. Barley and oats tend to fare better because the seed is protected by a husk. In fields with high slug pressure, farmers should drill their covers.

Why wait?

Farmers can end up losing many weeks of possible cover crop growth because they think they need to wait to plant cover crops until after a manure application. Many farmers have been successfully experimenting with applying manure to standing cover crops.

Liquid manure can be either broadcast or injected with a low-disturbance injector. More aggressive injectors are not very compatible with covers. Farmers should time the application either just after seeding the cover crop or waiting until it is more than 4 inches tall to reduce damage to the stand.

Negative experiences can turn a farmer off to cover crops. Using tried-and-true best management practices for cover crops can build small successes for the farmer and potentially lead to more acres covered and less soil lost to erosion.  end mark

PHOTO 1: This barley was aerially seeded into standing silage.

PHOTO 2: Barley residue is shown in the spring after the field had received a fall low-disturbance manure injection after the cover crop was planted. Photos by Heidi Johnson.

Heidi Johnson
  • Heidi Johnson

  • Dane County Crops and Soils Educator
  • University of Wisconsin Extension
  • Email Heidi Johnson

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