Some considerations for cover crops after small grains

The best time to seed a cover crop after small grain harvest is to chase the combine with the drill.

Oat, radish and flax cover crop seeded after early harvested cash crop. (Abbey Wick, Special to Agweek)

With small grain harvest coming, it’s a good time to make a cover crop plan and get your ducks in a row for making it happen. The best time to seed a cover crop after small grain harvest is to chase the combine with the drill. The earlier you plant your cover crop, the more biomass and overall benefits to the soil you’ll get. This means that deciding what your goal is, what your next crop will be and getting the seed ordered is key to getting this done.

A couple tips for determining your goal. Take a shovel to your field and dig a hole. What do you see in the soil? If you see platy layers (the soil literally looks like stacked dishes), then you may want to work on fixing compaction by using a grass species (like oats, cereal rye or barley) along with a radish which has quite a bit of force to push through the soil and open it up. If you see salts (white specs in the soil or yellow gypsum crystals), then you need to focus on water management to manage the salts. This means something as simple as letting the volunteer small grain re-grow or seeding a grass cover crop that will over winter like cereal rye to continue using water. If you see loose, non-aggregated soil (the soil looks powdery), then you can work on building aggregates. This is best done with a fibrous root of a grass species. Again, you can pick the cheap solution and just let the volunteer re-grow or you can specifically seed something that will overwinter (to work for you both in the fall and the spring) like cereal rye. Or maybe you see muck (the soil is saturated and you need to use up some moisture), then I would get a diverse mix seeded that has variable rooting depths to use moisture throughout the soil profile. This may include a grass, radish, adding in a sunflower or something else deep rooted to get down into the soil. If your soils/seedbed are excessively dry, then you need to really weigh the options and ask yourself, if you seed a cover crop, will it establish? Is it worth the money? If you are in a drought, you may not want to put seed out there to avoid the extra cost.

Next, think about what your crop will be on that field in 2021. If you are planning wheat or a small grain again, then don’t put cereal rye out there as a cover crop, unless you plan to take it to harvest in 2021. The rye will contaminate your grain. If you are going to corn, then you probably don’t want cereal rye either, unless you can terminate it 14 days prior to planting corn to avoid potential yield loss. If you are going to soybean, cereal rye is a great fit and you can plant green. Just watch the rye in the spring and terminate if it’s using too much moisture prior to planting soybean. If you are going to soybean and you have soybean cyst nematode issues, then avoid cover crops that are SCN host. We have a list of these on the NDSU Soil Health webpage (click on the Prevented Planting Link). If you plan to seed canola in 2021 or even if you have canola in rotation, avoid brassicas, like radish. Clubroot disease transfer from radish to canola is a real issue and not something you want to mess around with. I can’t think of many issues of cover crops before sunflower, flax or dry beans — just be aware of potential disease transfer between a cover crop host and the cash crop.

Lastly, get the seed ordered. If it’s in the shop, you have a better chance of getting it seeded quickly. If you purchase bin-run seed, be sure to get a sample and get it tested at the North Dakota State Seed Lab. For under $100 and a quick day or two turnaround time, you’ll have peace of mind that you aren’t accidentally seeding a contaminated cover crop across your farm. If your plan is to let the volunteer small grain grow, go for it. There’s no planning involved in that.

The bottom line is that if you want to seed a cover crop, planning is key so that you can get it seeded quickly. We have a lot of information on the NDSU Soil Health webpage (, so you can go there if you need more ideas. Also, thanks to John Stika (@humusphysicus on Twitter) for responding to my tweet requesting ideas for content this week! If you have things you’d like me to shed some light on in this column, please find me through Twitter (@NDSUsoilhealth) or send me an email (


Abbey Wick is an Extension soil health specialist at North Dakota State University.

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