By Jodi DeJong-Hughes
Extension educator
In Minnesota, small grain harvest is complete and sugar beet, sweet corn, corn silage, and pea harvest is well underway. With these early harvested crops, producers have an opportunity to consider planting a cover crop this fall, a practice that has many benefits. This may be a particularly good year to try cover crops, since soil moisture in many parts of the region is ideal for germination.
Cover crop success stories have been shared in almost every local and national Ag magazine over the past five years. Cover crops have many benefits, including improving water infiltration, reducing soil erosion, scavenging excess nitrogen and phosphorus, providing nutrients, using excess moisture, extending the grazing season, improving soil health, and providing a food source for pollinators.
How and where should a producer get started with cover crops? The best approach is to keep it simple. In fields where wheat was just harvested, one option is to allow the wheat to reseed itself without tilling the land. As long as the soil is covered, this would be considered a cover crop. However, this may cause issues by creating a wet mat of plant residue on the soil surface in the spring. A better option may be to seed cereal rye into the volunteer wheat, so the rye can utilize the extra moisture in the spring. When starting out, using one or two cover crops is an excellent way to get acquainted with their benefits. With lower commodity prices, expensive seed mixes are not necessary. The most popular choices are forage radish and cereal rye. Before choosing a cover crop, consider the following questions:
1. What is my crop rotation and harvest timing? If sugar beets have just been harvested, brassicas will not be needed in the cover crop mix (i.e. turnip, canola, or radish), as there isn’t enough time for adequate growth to justify the cost. Instead, plant a small grain or grass. If the field is going to wheat next spring, then do not use cereal rye as a cover crop. Instead, choose oats, so that any volunteers that come up in the wheat crop can be killed.
If cover crops are planted after August 15, use cool season crops. These may include forage pea, barley, wheat, and triticale. In our northern climate, there may not be enough time to truly benefit from a legume's nitrogen credit when they are planted in late-summer.
Herbicide carryover and rotation restrictions are another consideration when planting cover crops. Look at herbicide product labels or call your agronomist for exact restrictions. University of Wisconsin has a helpful, in-depth fact sheet that can be used as a guide: Herbicide rotation restrictions in forage and cover cropping systems.
2. Do I want a cover crop that will overwinter? A cover crop that overwinters will provide the best soil protection through the winter and into spring. However, it generally will need to be terminated before the cash crop is planted in the spring. A combination of cereal rye, which will overwinter, and radish (which will winter kill) is an example of a mix where the rye provides added soil protection, while the radish residue decomposes quickly. For a quick growing grain that does not overwinter, seeding barley in the fall is a good option. While typically winterkilled, it should be noted that turnips overwintered in parts of Minnesota and North Dakota in the 2015-2016 winter. However, if radish in the mix and there aren’t grazing cattle, then another cover crop that serves the same purpose as radish isn’t needed.
3. How should cover crops be seeded? There are several choices for seeding cover crops. They include a no-till drill, slurry seeded (keep manure agitated for a more even spreading of seed), broadcast and lightly incorporated for seed to soil contact, or by plane. If the soil is moist, all of these seeding methods are viable options. If the soil is dry, leaving the seeds on the soil surface will reduce germination and coverage during the fall. Oats are better equipped to be seeded a little deeper if soil moisture is a concern. Peas also need to be seeded deeper than most other cover crops. In general, when broadcasting or flying on cover crops, smaller seeds are a better choice: radish, turnip, flax, dwarf essex rapeseed, cereal rye or barley. Larger seeded crops, like peas, sunflower, etc., should not be broadcast or flown on.
Producers are encouraged to consult with seed dealers and other sources for selecting the right mix and rates for specific field and crop rotation situations. Consider visiting U of M and NDSU Extension websites, Midwest Cover Crop Council, and NRCS publications for more information.
Cover crops can be an excellent addition to crop rotations as they improve water infiltration and reduce erosion. Trying one to two species of cover crops and planting them in the early harvested fields will set-up the fields for long-term success.