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Selecting Cover Crop Species

COVER CROP

TRAINING MODULE

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Developed by

Dr. Rob Myers, University of Missouri and NCR-SARE

Reviewed by

Dr. Dean Baas (Michigan State University) and Dr. Marisol Berti (North Dakota State University)

Funded by

Walton Family Foundation

These training modules are being made available by free use of other educators through University of Missouri and the Midwest Cover Crops Council, which participated in the WFF project supporting development of these modules and provided many of the technical reviewers.

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There are dozens of cover crop species and varieties available

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Crimson Clover

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Factors to consider in selecting a cover crop

What time of year is the cover crop needed?
What are the goals for the cover crop use?
What planting method will be used?
How easy is the cover crop to establish?
What kind of soils are present?
What are the cash crops in the rotation?
How much does the seed cost and how available is it?

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Radishes

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Biology of the cover crop plant

Annuals – fastest plants at getting established

Winter annuals start growth in fall and generally require a cold period to flower
Summer annuals will flower in a single growing season
Cool season annuals do best in spring or fall
Warm season annuals thrive in the heat of mid-summer

Biennials

Two-year growth cycle, normally start growth in the spring or summer of one year and don’t flower and produce seed until the following year, e.g., sweet clover

Perennials

Plants that will live multiple years and can flower every year
“Weak” perennials tend to die out after a few years
Perennials are generally much slower at early above ground growth than annuals, as they are putting energy into roots

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Cover Crops (examples)

Fall planted

Cereal (winter) rye
Oats
Oilseed radishes
Annual ryegrass
Hairy vetch

Spring planted

Spring triticale
Oats
Austrian peas
Dwarf rapeseed
Clovers

Summer planted

Sorghum sudan grass
Foxtail millet
Buckwheat

Crimson clover in a Missouri field.

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What are the goals for the cover crop?

Soil erosion – need fast cover, good rooting, persistent growth – cereal rye, triticale
Soil compaction – deep rooting or taproots – annual ryegrass, oilseed radishes, sunflowers
Nitrogen fixation – legumes – Austrian winter peas, crimson clover, red clover, hairy vetch, sunnhemp, cowpeas
Nitrogen sequestration – cereal rye, other winter cereals, radishes
Disease/nematode suppression – Brassicas (eg. radish), or just good rotation practices – don’t use a grass cover crop before or after a grass cash crop (corn), avoid a legume cover crop before soybeans
Weed control – cereal rye is allelopathic to small-seed broadleaf weeds, Brassicas good at smothering winter annual weeds
Pollinator habitat – buckwheat, sunflowers, diverse mixes

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Oilseed Radishes

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What planting method will be used?�

Traditionally, most cover crop seed has been drilled or broadcast seeded. When broadcasting:

- the larger the seed, the harder it is to get good seed-soil contact, so more important to rough up the soil surface, and possibly roll or press the seed into the soil after broadcasting

- aerial seeding works best with small seeded cover crops like radishes; don’t use with large seeds like Austrian winter peas

Precision planters (like a corn planter) can work well for one or two species but not as well for multi-way blends of cover crop seed
Planting method will often be tied to planting date, and some species are more important to plant early in fall (like radishes) than others (like cereal rye)

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Photo credit Joel Gruver, Western Illinois University

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How easy is the cover crop to establish?�

Ease of establishment based on type of seed, method of seeding, time of seeding, soil conditions, and especially moisture conditions and rainfall.
In general:

Easier to establish – crimson clover, cereal rye, oats, wheat, triticale, radishes, other Brassicas (radishes, rapeseed, etc.)
Using mixes of cover crops can improve odds of success, especially if just broadcasting or “disking it in” – something is likely to grow!
Buying clean high-quality seed and good varieties can make a big difference – find out the tested germination – should be 85% or above.

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Hairy vetch and oats

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How hard is it to terminate the cover crop?�

Possible methods of control – herbicide, tilling, mowing, rolling, roller-crimper, grazing or easiest of all – winter!
With most mechanical methods, best success comes after cover crop reaches reproductive (flowering) phase
If using herbicides, cover crop needs to be actively growing to translocate the herbicide
Clovers not especially easy to kill with glyphosate alone
Really thick matts of covers (rye or mixes) can be tough to completely kill with a roller crimper
For beginning cover crop users, sometimes easiest thing is a cover crop that winter kills – oats, radishes
Crimson clover easy with everything except glyphosate, winter rye pretty easy to kill with glyphosate

This section of the talk is important because for many farmers one of their greatest hesitations in adopting cover crops is worrying that they will create a problem during spring planting of their cash crop. In other words, they wonder if that cover crop will be in the way or create a mess or simply be difficult to kill (terminate).

Farmer comfort level with termination can be increased by pointing out:

Some cover crops are easier to terminate, such as cereal rye
If they have a plan for termination ahead of time, things will go smoother
If they are really concerned about having to terminate, plant a cover crop that winter kills such as oats and/or radishes till they gain more experience

Another tip is that it is generally easier to terminate one species of overwintering cover crop than working with a mix, despite the advantages of cover crop mixes. So a first time user of cover crops may want to start out with just one species that will overwinter, thought that species (such as rye, triticale, wheat, or clover) can be planted with something that winter kills like oats or radishes.

Trying to terminate a cover crop with tillage may require multiple passes, depending on the tillage instrument used and the type of cover crop.

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Crimson clover

Photo of crimson clover in bloom, typically mid-April in the southeastern U.S., late April in the southern corn Belt, and around the beginning of May in the central Corn Belt or Pacific Northwest. Termination is relatively easy with if mowed or roller crimped after flowering starts, or by using 2,4D, but glyphosate alone may not kill it completely (so add 2,4D to mix).

Crimson clover was the most used legume cover crop in the national SARE/CTIC cover crop survey in 2015 and again in 2016 (last crop year surveyed).

Advantages of crimson clover

As a true winter annual, fits well for fall to spring cover cropping and gets off to a fast start. Can also be frost-seeded in spring and get good early spring growth.
Fall growth is more than most other legumes when planted in mid-fall. If a legume can be planted in late summer, such as late August or early September, winter peas may get more above ground biomass than crimson clover.
Produces a moderate amount of spring growth but not hard to plant into, doesn’t tangle up on planter like hairy vetch can potentially do. Also, doesn’t normally have the hard seed problems of vetch.
Farm families and their neighbors like the beautiful spring flowers

Disadvantages

Doesn’t overwinter as far north as some legumes (Interstate 70 rough dividing line) and doesn’t survive as well on poorly drained soils.

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What kind of soils are present?�

Good drainage important for some overwintering cover crops like crimson clover
Sandy soils may need a cover crop good at building organic matter and helping hold the soil from blowing
Claypan soils may need a strong rooting cover crop like annual ryegrass, sunflowers, or possibly radishes
Low fertility soils may benefit from a legume, but watch out if pH is really low (grasses can tolerate acid soils better than clovers and other legumes)
Sloping fields that are erosive need a fast-growing, persistent cover crop like cereal rye
Saline soils are challenging, barley is recommended

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Photo credit Joel Gruver, Western Illinois University

Example of oilseed radishes. Plants normally winter kill through most of the Corn Belt (however, radishes can overwinter in the true south). When the radish plant dies, the top growth starts to decompose, and having a relatively low C/N ration, will also contribute to accelerated decomposition of corn or soybean stalks still on the surface. That can provide a clean planting strip in the spring.

Some farmers trip to plant their corn seedlings next to the radish row to take advantage of not only the barer soil strip but also the higher nutrient zone near where the radish tuber was. Although the decomposing tubers initially leave a small hole in the soil, it often has disappeared by planting time even in no-till fields, depending on rainfall and soil type. Of course if the holes are still present offsetting the planting row from the radish row is helpful to avoid excessive seed depth on the corn (or soybean) seedlings.

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What are the cash crops in the rotation?�

Try to have a diverse rotation in terms of plant families and plant types
Can really help to add wheat to a corn-soy rotation in combination with cover crops, especially more northern areas
May want to adjust cash crop planting dates, herbicides
Mixes of covers adds biodiversity
If grazing can be done with covers, that influences choices

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Midwest Cover Crop Council Cover Crop Decision Tool�

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MCCC Cover Crop Selector Tool

Click the cover crop name for additional information, including seeding depth.

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MCCC Cover Crop Recipes for Midwestern States

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What does the seed cost and how available is it?

Cheap and readily available ≠ good
Buy quality seed of known varieties and appropriate varieties – really important for annual ryegrass
Order early, seed often in short supply late in season
Inoculate legumes (keep inoculum cool)
Mixes of species have pluses but can be more expensive
Consider applying for government cost-share programs
Invest in your cover crop like you would your cash crop!

Buy good seed, don’t plant too thinly, and plant correctly at the right time

Cost of cover crop seed is a factor on many farmer’s minds, especially those considering using a cover crop the first time. Seed cost can be completely covered by incentive payments from state or federal government, but regardless of whether incentive payments are available, keeping seed cost moderate will be a priority for most farmers.

Although the temptation is to buy the cheapest source of seed, such as bin run cereal rye that a neighbor has grown, it’s important to stress with producers that good quality seed is worth the investment, just like for commodity crop seed. Getting clean, weed-free seed of high germination percentage (85% or above) is important.

Farmers should ask the dealer if the seed has a seed tag, what the germination percentage is and what the percent of weed seed and foreign material is.

Much of the cover crop industry currently involves seed that is “Variety Not Stated” or VNS. However, improved cultivars are becoming more available for cover crop use every year, and in many cases it can pay to select an improved variety that has proven performance in the local region.

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Sources of Cover Crop Seed

Companies specializing in cover crop seed sales
Forage seed companies
Local seed warehouses/retail sellers
Ag retailers, such as fertilizer dealers
Other farmers*

* When buying from other farmers

Be sure seed has been recently tested for germination percent
Ask for a seed tag showing percent foreign material, weed seed, noxious weeds, and percent germ
Be aware of transport restrictions across state lines from some sellers

Best to buy named varieties instead of variety not stated (VNS)

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Buying Cover Crop Mixes

Sources – Some companies sell only pre-packaged sets of cover crop mixes or may sell only individual species, others will custom blend

Tips

Seeding rate should be cut back to reflect total number of species
Ask about inoculation on legumes – best to order inoculum separately, keep it cool such as refrigerator after received, and then stir in the inoculum shortly before planting; may work to have seed company do it as long as its done in cool weather shortly before shipping, and seed will be stored in cool, dry conditions.
Seed segregation is worst when only two species and seeds are round and similar size. If using three or more species and some difference sizes and types of seed are used, segregation is usually less. Still, check the seed and make sure it doesn’t need to be remixed.

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Many different cover crops are available today

and more are coming on the market.

It pays to match the cover crop selected to the specific needs in the field.