With the thought of prevented planting acres looming, preparing those acres for next year's crop will be important. Rather than leaving those acres fallow, getting a full-season cover crop planted this year may be just the ticket to build soil aggregation, improve water management, ramp up the soil biological component, manage weeds, amongst many other benefits.
Here are some considerations and tips for getting started:
• Check out your RMA Guidelines for planting dates and acceptable uses (web search: RMA Prevented Plant and/or talk with your insurance provider).
• What will your next year's crop be on each particular field? Asking this question will help you pick your goals for each field, select a cover crop mix that will help you achieve those goals and limit potential negative issues.
• Do you have any herbicide residual on the field and what will you use as a burndown prior to planting a cover crop? There is no sense in having a specific cover crop as part of the mix if it won't grow because of herbicide residual, so be sure to check this prior to ordering mix. If you have questions, there are resources posted on the North Dakota State University Soil Health webpage, talk with your agronomist or contact an NDSU Extension county agent. A weedy cover crop stand is also a bad idea, so make sure you do a burndown prior to seeding cover crops.
• What do you want to spend on a mix? The goal is to not go overboard, but to do enough to achieve your goal. There is a great opportunity to get a lot of growth out of a full-season cover crop, but doing a 25-way mix that is expensive may not be a good fit.
• How are you going to seed the cover crop mix? Consider seed size and what is included in the mix. Having both small and large seed in a mix can be a challenge because of seed separation and choosing a seeding depth (I usually split the difference between the deepest and shallowest seeding depth). Keep in mind that we aren't shooting for perfection here, it's a cover crop. That being said, having uniformity in cover crops seeded across the field this year and what that residue may look like going into next year is an important consideration. The goal is to just get it done.
• Do what you are comfortable doing - if you don't know a species listed in a pre-made cover crop mix or don't know how you're going to manage it, then don't include it in the mix. It is perfectly acceptable to seed a prevented planting field to just oats with a little bit of radish if it helps you achieve your goal. Don't feel like you have to include more than what you're comfortable including, you can design your own mix.
Let's lay out what could be used in one scenario, just to give an idea of what the thought process is. This is just an idea that I have, so you'll want to consult with your agronomist and think things through to customize to your farm.
Field going to corn next year, goal to manage some minor salinity issues.
• Forage barley. less than 30 lbs/acre* so that the other species in the mix can compete, but adjust as needed or recommended. Benefit: salt tolerant and provides good coverage.
• Radish. 2 lbs/acre is all you need. Good to use if you've already applied fertilizer to a field and weren't able to get it planted, radish may help capture some of that nitrogen, but keep in mind that we aren't sure when it would be available again to crops in following years. But at least it won't be leached. Benefit: break up compaction and capture nitrogen.
• Millet (less than 30 lbs/acre) or Sorghum (less than 2 lbs/acre). Benefit: warm-season grass component to the mix, fibrous roots and sorghum has a high water use.
• Sunflower. not sure on seeding rate, so check on that with a seed company or by preference for your fields. Only use if you don't have sunflowers, canola, or beets in rotation for disease carryover reasons. Benefit: deep taproot will dry the soil.
• Faba bean. Use low rate because seed is expensive, but a high enough rate to get a benefit. In the past, I've used 20 lbs/acre in a mix, but it cost me some cash. Be sure to inoculate with faba-bean specific inoculant. Benefit: faba produces great nodules when inoculated; residue is upright and is the most efficient nitrogen-fixing legume. If using forage peas, consider that the residue may wrap around the planter the following year. I haven't seen much out of clovers for establishment so it's difficult for me to see the benefit. I stay away from legumes like hairy vetch and anything else that can take over a field.
*Rates need to be adjusted, especially for the grasses, depending on what is put into the mix - so if barley is included and not millet, then be on the higher end of the seeding rate. If both barley and millet are included, drop the seeding rate down for both. The seed company can guide you on this aspect of the mix, but at least you have a ballpark starting point.
I've put cover crop and prevented planting resources on the NDSU Soil Health webpage (ndsu.edu/soilhealth). There are some video links where Marisol Berti, NDSU forage and cover crops production researcher, takes us through cover crop plots so that you can see what the different plants look like, there are photos on different cover crops and what the seeds look like. There's also a link to the ARS cover crop chart that has some excellent information. These are all resources I've used in the past to make decisions about cover crops.