After small grains, we typically try to get our cover crop mixes seeded by August 15. That date has blown by us and it is now mid-September with some wheat still being harvested.
This late harvest has made it very difficult to get a cover crop seeded, among many other challenges in 2019. Seeding diverse mixes that include radish, turnip etc. or mixes that include several species with a weak promise of overwintering accompanied by a high cost (hairy vetch, Austrian winter pea, winter-hardy clovers) is not worth the effort or money at this point in the season. There are only two cover crops that stand a chance of over wintering reliably in North Dakota - cereal rye (or winter rye) and winter camelina.
My suggestion is to drop the other species from the mix and go with one or both of these tried and true winter-hardy cover crops to get something in the ground this fall so it can manage moisture in the spring. With the cooler temperatures we've been having, set your expectations now that you may not see much growth this fall, but it will grow in the spring.
Tips for cereal rye
We know that cereal rye seed varies greatly in size and giving a pounds per acre rate is less than ideal, but that's what I know, so for now we'll go with that. For starting points in a mid- to late-September time frame for our region, I would be at 60-70 pounds per acre cereal rye seeded on high clay soils. As you get into sandy soils, starting lower at 40-50 pounds per acre rates seeded is a safer bet. Notice that these rates are "seeded" and not "flown on." If flying on the cover crop because access to the field is limited, then bump up the rates by 10 or so pounds per acre. Seeding rates increase as we get later in the season.
Seeding a cover crop at this point is going to be better than broadcasting it because seed to soil contact helps with establishment. But some fields are very wet, time is getting short and panic is setting in on how we are going to use up excess moisture for planting next year, so broadcasting may help you sleep at night. You can give it a shot, just keep your expectations in check.
Take good notes on which fields you put cereal rye into this fall. You will not want to accidentally seed a wheat crop on those fields next spring because of contamination issues. Cereal rye before wheat is a hard "no", before corn is a "make sure you manage it", i.e. spray it, before planting, and a "no brainer" before soybean especially in wet conditions.
Tips for winter camelina
Seed for this cover crop is being multiplied in our region because typically spring camelina has been what is available. But there is some winter camelina out there, just be sure to specify and ask where the seed is sourced. If the seed comes from Montana, it is likely to be spring camelina. But if it was grown in North Dakota, it could be winter camelina.
Winter camelina is a broadleaf that is very winter hardy with a nice tap root. It is sensitive when it comes to residual herbicide, so it may be difficult to establish, just be aware of that. It is also a very small seed, meaning seeding rates are low (definitely less than 2 pounds per acre in a mix), but it's not something that can be put in a mix with cereal rye and seed it all at the same depth. Broadcasting it on the surface or shallow seeded is the ticket.
Camelina may be a good option before corn, which is how we are currently evaluating it in our research.
Cereal rye and/or winter camelina cover crops can still be used as a tool to help us for next year, but let's keep it simple and cheap. I'm not one to tell people what to do, but I do want to provide some starting point or idea of what I would do at this point in the season. These are just recommendations based on what I see farmers trying or discussions I've had up to this point.
I always recommend that you go with your gut, pick cover crops you know you can manage and adjust rates based on comfort level and knowledge of your system. After all, you know your system best.