Ask Dr. Dan
By Dan Davidson
DTN Consulting Agronomist
Devoted cover croppers are feeling the window close on seeding cover crops. This fall harvest is running about two weeks behind in many areas. That's complicated seeding into standing crops to get a good stand and delayed direct seeding. After the poor stands many experienced last year, some growers are understandably worried about the prospects.
I have seeded covers between early September (aerial) and Dec. 21 (drilled). However, it is true that planting later changes your options and should alter expectations.
Location makes a difference in late cover cropping decisions. Our family farm is about 100 miles north of I-80 and my experiences are primarily based on that location. Growers south of I-70 can typically aerial seed into early October or wait and seed directly after harvest. The aerial seeding window shortens as one moves north -- generally it is recommended no later than the second half of September for those farming between I-70 and I-80 and first half of September north of I-80.
In general, the earlier you can plant in the fall, the greater the number of cover crop species you can plant. Aerial seeding buys more time for fall growth for species that will winterkill. Cocktails of fall cover crops that include grasses, brassicas and legumes, need to be flown on by the first two weeks of September north of I-80. You are limited to grasses such as winter cereals or annual ryegrass that will overwinter when the calendar rolls past mid-September in that region. Move that date to late September for the I-70/I-80 corridor and mid-October south of I-70. Of course there is nothing wrong with seeding earlier if the main cash crop is at the right stage to fly on cover crop seed.
Aerial seeding works best when the canopy begins to open up. In corn, that's when the leaves above the ear and the ear leaf have turned brown. When seen from above, about 50% of the soil surface should be exposed to sunlight. Overseed soybeans when about 50% of the soybean leaves have turned yellow, letting about 50% of the sunlight reach the soil surface. While the crop may be at the right stage to aerial seed, we have probably moved out of the window when you can plant a diversified cocktail north of I-80 this year. There's still time to aerial seed south of I-80 for a least two more weeks.
Once we move into October, decisions change radically because aerial seeding is of less benefit and growers are restricted to planting cereals or ryegrass unless south of I-70. In my experience, I do not expect much fall growth when I seed in October, but I do expect to be able to row the cover crop. Once we hit November or December, a winter cereal can still be seeded, but I don't expect to see any growth until the following spring. The beauty of planting a cover crop like rye is that it can be seeded anytime in the fall and even frost seeded in the winter and it will survive and establish itself come next spring.
Cereal rye and annual ryegrass are the basis for many cover crop programs. Cereal rye can be seeded any time right up until the soil freezes solid in December. Regardless of when you plant it, it seems to come up and grow in the spring. Annual ryegrass, known for its ability to produce more root biomass, doesn't tolerate cold weather without winter snow cover and is, in my opinion (not everyone agrees on this point), a risky species to plant north of I-80 because you don't know what the winter will bring.
I did drill 20 acres of ryegrass last fall along with 40 acres of cereal rye during the second half of October and I was able to barely row both crops this spring. It was so dry, cold and open (no snow) all winter that I inadvertently frost-seeded ryegrass and it survived the winter as seed until it germinated this spring. Had it been a moist fall, the ryegrass seed would have germinated, and I believe the ryegrass probably wouldn't have survived the winter.
If you wait until after harvest to seed, you have a few methods available. Usually your choice is a trade-off between acres planted per hour or day and desired plant stand. You can plant with a drill or larger 30-, 40- and 60-foot planters with sorghum plates. Placing seed in the soil always gives you a better stand and takes less seed. Or you can broadcast seed over the residue and cover a lot of acres rapidly.
For example, I will drill rye at 50 lbs. per acre. I increase the rate to 70 lbs. if the seed is broadcast and incorporated and I raise the rate to 90 to 100 lbs. per acre with straight broadcasting. I prefer direct seeding because I appreciate a very good stand, but this is personal preference.
It's not too late to consider planting covers, but factor your expectations into the decision and select the most appropriate species and planting method for the time you are seeding.
Dan Davidson can be reached at AskDrDan@dtn.com
Follow Dan Davidson on Twitter @dandavidsondtn
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