MINNEAPOLIS — Is it worth planting a cover crop to use for forage in a drought? Any forage produced will be that much more valuable this year, but what is the likelihood anything will grow if you put seed in the ground? These are tough questions to grapple with this year, especially since many small grains have already been harvested and corn silage harvest is right around the corner.
- The risks of seeding a cover crop in a drought are that dry soil conditions mean cover crops may not germinate until rainfall is received, or they may germinate but run out of moisture and die.
- The time and energy involved, in addition to seed and equipment costs, should be carefully considered before seeding a cover crop.
- If adequate moisture is available and establishment is successful, you have the potential to produce valuable and high-quality forage and gain soil health benefits (Table 1).
- Even marginal establishment success will provide some protection from wind and water erosion, especially on acres with minimal residue left following harvest.
To seed or not to seed?
Most areas under moderate to extreme drought stress do not currently have enough soil water to germinate any kind of seed you plant, especially at the shallow depths cover crops should be seeded for successful establishment. Establishment success will be at the mercy of future rain showers. Unfortunately, dry conditions will likely continue for the next several weeks. Some small grain fields that have been harvested received several inches of rainfall since physiological maturity, however, so there may be some soil water available in the upper soil profile.
Do some digging to check for soil moisture availability. If you find moisture, how deep would you need to seed to reach it (and is this too deep to seed a cover crop)? If you could time seeding before a rainfall event, this would greatly increase the chance of successful establishment.
Also consider how much soil moisture you need to “bank” for next year. Cover crops will use soil moisture that may be needed for next year if the drought continues. On the flip side, cover crops can help reduce runoff and increase soil infiltration rates when it finally rains. The potential positive and negative impacts of a cover crop on soil moisture in extreme drought conditions are tough to balance and predict. Regardless, having some type of ground cover will help reduce soil erosion potential.
- Avoid tillage to preserve moisture and residue from the previous crop, which helps minimize erosion.
- Control any weeds prior to seeding to prevent weed seed production and minimize competition.
- If you seed a cover crop, utilize a no-till drill that can place seed into moisture with a firm seedbed. The seedbed is much more important in dry conditions, meaning a good drill with depth control and press wheels is essential.
- Seeding rates may need to be increased due to dry conditions.
- Don’t broadcast seed near the soil surface and expect it to work. Hot and dry conditions will mean a seeding failure unless you have irrigation.
- Species selection should be based on
- When seeding occurs
- How and when you plan to utilize the forage
- How deep you need to seed to reach soil moisture
- Seed cost
- Herbicide rotational intervals
If you decide it is appropriate to seed a cover crop for forage, one of the main goals should be keeping seed costs down. With the chances of successful establishment being marginal even with good depth control and seed-soil contact, we don’t need to spend additional money on seed.
If you have 6 weeks until the first killing frost and need fall forage, seed Foxtail millet, sudangrass, or a sorghum x sudangrass as these are drought-tolerant and will perform better in hot, dry conditions than other cover crops (Photo 1). In many areas of Minnesota, however, it is getting too late to seed warm-season grasses.
Once we get into mid-August, oats and other cool season cereal crops are good options for fall forage without spending significant money on seed (Table 1). If little soil moisture is available, consider seeding spring cereals with a winter cereal crop like cereal rye to provide some fall forage with the potential for spring forage as well. Brassicas are another good option to include if the cover crop will be grazed, as they withstand cold weather and frost well. Brassicas also retain quality well into the winter and can also work well as a mixture with warm-season crops.
Source: Grev et al., (2017). Agron. J. 109: 1-12.
If you don’t need forage this fall or are not confident you will have sufficient moisture yet this year to produce any fall forage, seed cereal rye. Cereal rye is the most drought-tolerant small grain so it should establish better than other small grains under dry soil conditions. If dry conditions prevent germination after seeding, cereal rye seed will remain viable and germinate later once there is adequate moisture. Seeding in September is preferred for cereal rye, unless fall grazing is desired. If rainfall is received before mid-September to germinate rye, it should put on enough fall growth to survive the winter and regrow next spring, producing forage that can be grazed, hayed, or chopped in the spring.
There are other cover crop species one can consider to seed for forage this fall, but moisture will be the limiting factor in most situations. Mixtures may be a good way to hedge your risk this fall. For example, seeding oats, cereal, rye, and some brassicas may provide opportunities for fall and/or spring forage depending on when rainfall is received.
Consider herbicide restrictions
Pay attention to any herbicide rotational restrictions listed on labels if you plant a cover crop for forage. The University of Wisconsin has published a helpful resource that lists the herbicide rotational restrictions for cover crops used as a forage, but be sure to check the herbicide label for the most recent updates. (https://ipcm.wisc.edu/download/pubsPM/2019_RotationalRestrictions_final.pdf)
Selecting forage cover crops for prevented plant acres (https://blog-crop-news.extension.umn.edu/2019/07/selecting-forage-cover-crops-for.html )
Selecting forage cover crops for small grain stubble fields (https://blog-crop-news.extension.umn.edu/2017/08/use-small-grain-stubble-fields-to-boost.html)
Midwest Cover Crop Decision Tool (https://mccc.msu.edu/selector-tool/)
U of MN Cover Crop Website (z.umn.edu/cover-crops)
— Jared Goplen, Liz Stahl, Craig Sheaffer, Nathan Drewitz, and Troy Salzer, University of Minnesota Extension
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