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If you want to plant a cover crop and haven’t made plans, it’s time to start thinking seriously about it.

Corn and soybean harvest has begun in the south and will move northward as the crop matures, so planting cover crops is on some farmers’ minds. Covers (as cover crops are now affectionately known) provide a number of benefits from protecting the soil, scavenging residual nutrients, adding organic matter and improving soil tilth to increasing soil biological activity. Also, the release of carbon dioxide via soil respiration provides a source of carbon dioxide to feed photosynthesis, which is the basis of yield. Thus, a healthier soil will release more carbon dioxide and just might increase yield.

Now that we are heading into fall harvest, it’s a good time to decide what your goal is and to think about when to plant covers, what species to plant and how to plant them.

Windows of planting: Covers can also be planted in the fall after annual row crops. Planting covers in the fall is most challenging because of the limited amount of time that remains, particularly north of I-70 and I-80.  Of course it is easiest to wait until after harvest to seed, but that limits the time remaining for fall growth. Other options are to plant early maturity corn or soybeans (10 to 15 days shorter maturity than average corn and one less maturity group for soybeans). You can harvest these crops early and then immediately seed a cover. Or you can aerial seed into a standing crop before maturity. Your goal is to get the covers planted so you have at least 4 weeks before the first hard frost.

What species to plant: There are a large number of species that can be planted as covers, but after corn and soybeans that list is limited. The list includes winter barley, rye, wheat or triticale; annual ryegrass; radishes, turnips and brassicas (rapeseed; crimson clover; winter peas; and hairy vetch. You can also include oats if planted early enough to give some fall growth (oats will winterkill early). If you want species that eventually winterkill, stick with radishes, turnips, rapeseed and oats. However, if you want species that grow into the spring and need to be terminated, stick with cereals, ryegrass, winter peas or vetch.

Cereal rye and annual ryegrass need special attention as they are both common winter covers and the basis for many cover crop programs. Cereal rye is an easy crop to seed any time in the fall right up to the time soil freezes solid in December. Regardless of when you plant it, it seems to come up and flourish in the spring. Annual ryegrass is known for its ability to produce more root biomass, which is the good for the soil. But it doesn’t tolerate cold weather well without winter snow cover and is a risk planting in the northern Cold Belt. In my opinion, lack of snow cover or a very cold winter make it risky to plant north of I-80. Some would disagree.

How to plant: Planting covers can be done by aerial seeding before harvest and broadcasting, broadcasting and incorporating, or drilling after harvest. When seeding a cover you want good and consistent coverage across a field, but remember you aren’t planting a crop to harvest. Some producers are happy with seeding at a lower rate, say 30 to 40 lbs. per acre of rye compared to 50 to 60 lbs. or a bushel per acre (when they would normally plant 90 to 100 lbs. per acre as a cereal cash crop).

Growers can aerial seed into standing corn and soybeans before the crop is mature, yet early enough to provide some fall growth. It would be ideal to aerial seed around the last week of August or first week of September and then have a round of rain for germination. But you need to aerial seed when there the canopy begins to open up and lets seed and light fall through. In corn that is when the leaves before the ear and even the ear leaf turn brown and, when seen from above, about 50% of the soil surface is exposed to sunlight. As for soybeans, fly on seed when soybeans are showing about 50 percent yellowing of leaves. At that time about 50 percent of the sunlight will be reaching the ground.

One of the keys to planting covers is to plant them early and as quickly as possible, especially if you have a lot of acres to cover. Planting with a 15-foot drill is very slow, but broadcasting a 50-foot spread or planting with a 40- or 60-foot row crop planter with sorghum plates is very quick. If I drill rye, for example, I seed at 50 lbs. per acre. If I broadcast and incorporate I raise the rate to 70 lbs.; and if I just broadcast only I raise that again to 90 lbs. per acre. However, I like drilling because I appreciate getting a very good stand and I like rowing the rows.

If you are considering planting a cover crop, start simple and on a few fields, keep the number of species to a minimum and figure out what planting method works best for you. Farmers who have excelled with covers and become leaders in this movement have done so because they started simple and then built on what they learned.

Agronomist Dr. Daniel Davidson posts blogs on agronomy-related topics. Feel free to contact him at djdavidson@agrwrite.com.