Ideas for using cover crops and tips to avoid mistakes
Wheat harvest (and harvest for other short season crops) is full speed ahead. With the early harvest, some of you may be thinking about seeding cover crops. Here I will share information on how to get started and how to avoid mistakes, along with seed selection for seeding or flying on cover crops post-harvest.
First thing's first — deal with residue before seeding a cover crop. Cover crops can do a lot of great things, but they can't solve residue management issues at harvest. The easiest way is to make adjustments to the combine or consider using a stripper head for wheat. If your residue isn't spread evenly and forms a thick mat on the surface, you may need to run a harrow over the residue to make it a little more even to avoid hair-pinning next spring.
TIP from Twitter: Run the harrow at a 45 degree angle to the combine heading and let the residue bunch up. Clean it out when you are done with the whole field. Be sure to do this when the residue is dry.
Next, figure out what you want to accomplish with a cover crop and what your next crop will be on that field. If you want to use moisture in fall and spring and are going to soybean the following year, cereal rye is a great choice. If you want to create dark strips to help the soil warm up before corn, bio-strip till may be for you. Using a planter to seed radish (and other cover crops like faba bean or flax — that's what I'm doing at the SHARE farm) on 22 or 30-inch row spacing will move some residue aside and get a dark residue on the strips where you are going to plant corn. TIP: If seeding just radish, use a sugar beet plate to seed at low rates.
When picking a species to achieve your goals, you do not want to use any warm season species if seeding after Aug. 15 (for the Northern Plains). Having cover crops that will grow in cooler conditions and can tolerate some frost will give you more bang for your buck. TIPS: Don't use clovers later in the season because we don't get much growth and they are expensive. Also, drop the expensive species from the mix as you get later into the season. After Sept. 1, I'm only seeding things like cereal rye or maybe barley.
My go-to species and reasons for using those species are:
Radish (for the tap root and it winter-kills somewhat reliably).
Turnip (for grazing; TIP: No turnips before soybean because of overwintering issues that can lead to turnips getting stuck on cutter bars during soybean harvest).
Dwarf essex rapeseed (nice tap and fibrous roots, tolerates frost, but can overwinter so watch for it in the spring; TIP: Don't use before or after a canola crop because it has the same root structure).
Cereal rye/Winter rye (for overwintering and weed competition; TIPS: Bump up rates if you seed later in the fall. Don't seed it around the perimeter of your fields if you have wheat in your rotation so you can effectively spray it all out without spraying your ditches).
Winter wheat (use when it's in the bin or when you don't want cereal rye on your fields).
Barley (for saline soils — this is your best salt-tolerant option, but it will grow later into the season and can create a "tough" residue).
Oats (mellow residue, winter kills, use before a wheat crop; TIP: Not good for saline soils but great for using on sandy soils)
Flax (dark residue, can help prime the soil for corn with mycorrhizal fungi; TIP: Lots of species are mycorrhizal, so this is not exclusive to flax and you'll still get that benefit by having a grass in the mix if you don't want flax)
Faba bean (dark residue, great root structure, cold tolerant but expensive; TIP: Try to keep faba separate from smaller seeds in a mix if your equipment has two tanks. That way you can get the faba a little deeper in the soil)
Peas (grow fast, residue may be issue for tangling in planters in spring; TIP: You can use peas for bio-striptill and seed them between where you will plant corn to get it away from equipment)
Once you pick what you want to plant, take a look at herbicide residual and make sure what you want to seed will actually grow. We have some guidelines on the NDSU Soil Health home-page (ndsu.edu/soilhealth) labeled as "Cover crop herbicide residual information from Lee Briese, Centrol Ag Consultant." Adjust accordingly so you don't waste money on seed that won't germinate.
Then consider your seeding method. When flying on cover crops, use small seeds (radish, turnip, flax, dwarf essex rapeseed) and some kind of "carrier" like cereal rye, winter wheat, barley or oats. Think about the seed weight of the carrier seed — for example, oats don't broadcast as far as cereal rye from a plane, so airplane passes need to be closer together when flying on oats. Also, bump up the rates when flying on seed versus seeding it in the ground.
We're always learning, so share what does and doesn't work on Twitter (tag @NDSUsoilhealth) or by sending me an email (firstname.lastname@example.org). Sharing what we learn is how we move forward with using cover crops quickly.
Thank you to all the farmers who have been sharing what's happening on their farms.