Making Cover Crops Work in Northern Regions

By Sarah Hill, Associate Editor, No-Till Farmer

South Dakota NRCS agronomist Jason Miller shares tips on customizing a cover crop system to less-than-ideal growing conditions.

Cover crops have been slower to catch on in northern regions because there are more obstacles than in warmer climates. A shorter growing season, fewer days of sunlight, and in recent years, more moisture, have all proven challenging for northern growers who may have considered cover crops.

At the 2020 National No-Till Conference, Jason Miller, an NRCS agronomist based in South Dakota, shared insights on how cover crops can be used to meet growers’ objectives, even in northern climates.

Miller has been with NRCS for 30 years. He’s been working with the Dakota Lakes Research Farm near Pierre, S.D., since 1997. During his career, Miller has learned that cover crops are just one component of a soil health system, in addition to crop rotation, no-till, nutrient management and integrated pest management.

According to Miller, increasing soil health and/or quality should be the main focus of any cropland system.

“Restoring soil resilience is a must,” he says. “Soil resilience, increasing organic matter, improving soil biology, improving water filtration and decreasing soil compaction ultimately add more dollars in your pocket and improve crop production.”

Jason Miller, NRCS Agronomist

SELECTING COVER CROP SPECIES

Miller suggests that growers consider multiple objectives when selecting cover crop species. “What will the following year’s cash crop be? Will it be corn, soybeans, wheat? What herbicides have been applied to this year’s cash crops and what implications do those have on what you want the cover crop to do?” he asks.

“If you’re looking to produce a lot of biomass quickly, raising brassicas may be the way to go,” says Miller. “Within 30-45 days, as long as moisture and nutrients are adequate, there is a lot of growth.”

“They’re excellent at nutrient scavenging,” Miller adds. “In South Dakota, we have to limit the brassicas in the mixture, especially as you go west, due to the brassicas breaking down the previous crop residue too quickly the following summer.” Previous crop residue is extremely important to the performance of the current cash crop in reducing soil water evaporation.

“Farmers in the eastern part of the state don’t like residue because things are wet, so they want to plant brassicas. It really doesn’t start breaking down that residue in time to help you with planting. You start seeing that residue disappear from July to September.”

“Peas are an excellent cover crop,” Miller says, “but growers should be cautious not to mix species of peas that are used as a cover crop if they are also growing pulse crops for a cash crop, due to the risk of carrying over root diseases.”

Miller says what you want to get out of your cover crop should drive what you put into it. “That means if you’re planning to graze it, it may make sense to add some fertilizer to get more biomass if nitrate N soil test values are low.”

“If you’re just growing covers for soil health purposes, then you don’t need fertilizer. If you take off a high-yielding wheat crop with questionable protein, then you probably have a deficiency, so you’re not going to get a lot of cover crop growth out of that.”

Miller says he always adds oats and flax to a cover crop cocktail because they’re friendly to soil biology and encourage mycorrhizae that help extract water from the soil profile.

For fields with shallow compaction, Miller recommends using annual ryegrass, oats and other small grains.

“We have cover crop species that will address surface and sub-surface compaction,” he says. “I like those with fibrous root systems, like small grains, for surface compaction. When you get into deeper compaction, that’s where the brassicas like radish and rape tend to help alleviate the sub-surface compaction.”

“Providing weed control with cover crops is kind of a no-brainer,” Miller says.

“Anytime we can get something green growing out there that’s going to provide some competition for weeds, it’s a positive, whether it’s germinating or growing.”

PLANTING COVER CROPS GRAZING COVER CROPS

Miller says that although the Dakota Lakes team has conducted offsite research on flying/ broadcasting coated cover crop seed, drilling has proven to be the most reliable seeding method in his experience. Other producers that Miller has worked with have been successful with aerial broadcasting cereal rye into corn during the last week of August and into the first couple weeks of September or flying cereal rye into standing soybeans.

“Generally, the rule of thumb is, the smaller the seed, the shallower you plant it,” Miller says. “I’d rather it be planted just a little too deep to make sure you cut through the residue layer. So, make sure you’re adjusting your drill accordingly for the residue levels. Be conscious of that and make sure you’re getting it in the ground and not into the residue duff layer where it has a high chance of not germinating.”

“Broadcasting cover crops into a cash crop stand that’s at V5-V6 usually does not go very well,” says Miller. “Most producers sacrifice weed control and small cover crop seedlings struggle to compete against weeds that have already started growing.” Miller only recommends broadcasting covers into a cash crop stand on fields with a clean weed history.

“There’s not enough competition out there for the weeds. I can’t afford for weeds to go to seed.”

Miller notes that the results of aerial seeding depend on the temperature during the last half of September and all of October.

Miller adds that covers provide good livestock grazing and forage potential and says another option is to plant a full season cover crop instead of just the cash crop plus a cover crop.

“I really recommend this in western South Dakota, where we just don’t get enough moisture most years to get a viable cash crop and get a cover crop going after small grain harvest,” Miller says. “With a full season cover crop, if the grower has cattle, it’s a lot more profitable. Some big cattle operators are even doing this in eastern South Dakota.”

For growers who are looking to graze brassicas, forage rape, turnips, hybrid brassicas, Miller notes that collards and kale produce a lot of leafy material.

“If the temperature is below average, you won’t get a lot of growth,” he says. “Once it gets up, it’s all temperature driven. You have to have the moisture to get going. So, it’s extremely difficult to get a diverse mix going in a corn/ soybean rotation.”

According to Miller, the best time to plant a cover crop in South Dakota is immediately after small grain harvest, because that’s when some soil moisture is most readily available due to previous crop canopy protecting the soil surface water moisture levels from evaporating during the summer heat.

“If we plant a little later, we’re going to get less growth,” he says. “There’s advantages and disadvantages to this. Delaying planting allows us to get our small grain volunteer growth and kill any existing weeds before planting that cover crop.”

Miller recommends a cover crop planting date of August 5 in South Dakota.

“That date moves a little, a week to 10 days from year to year, depending on the temperatures later in the fall,” Miller says. “If we delay planting to the middle of August, then we cut our biomass production in half and use less water.”

THINKING ABOUT COVER CROPS?

Every field is different whether it be the soil type, crop rotation, weather or climate situation, or cropping system. Farmers considering how to integrate the use of cover crops to their fields can visit with agronomists, grazing or other specialists at USDA Natural Resources Conservation Service and our partners, the SDSU Extension and SD Voices for Soil Health Mentor Network. To find the Cover Crops Resources web page, visit www.sd.nrcs.usda.gov, then keyword search “Cover Crops.” One-on-one, in-field consultations with NRCS specialists are available for farmers, landowners, or managers as they explore options for their fields that fit their business operation. Contact your local USDA Service Center or go to bit.ly/ContactNRCSSD to find phone numbers and email addresses. On the NRCS South Dakota Cover Crops Web Page (usda.gov), you will find detailed fact sheets for various species as well as links to industry planning aids such as the: NRCS Table 1: Cover Crop - Common Species and Properties, a link to the Managing Cover Crops Profitably, 3rd Edition; Cover Crop Chart (v.1.2) of the USDA Agricultural Research Service chart; and the Excel spreadsheet Cover Crop Seeding Plan and Record. The SD NRCS Cover Crop Technical Note (Updated October 2020) is an excellent tool that serves as a guide for installing cover crops according to the practice standard found in the South Dakota (SD) Natural Resources Conservation Service (NRCS) Technical Guide. “Soil resilience, increasing organic matter, improving soil biology, improving water filtration, and decreasing soil compaction ultimately add more dollars in your pocket…” ~ Jason Miller

“For grazing, we like to use turnips, rape, radish, rye oats, triticale, sorghum-sudan, sugar beet, sunflower, field peas and common vetch,” Miller says, adding that many of these help combat soil compaction as well because these cover crops have deeper tap roots.

“This is important because walking cattle can put 48 pounds per square inch (PSI) of pressure on the soil, resulting in compaction if soils are wet,” explains Miller.

“Where we’re grazing, we need to be cautious about not grazing in wet soil conditions. I prefer frozen ground.”

IMPORTANCE OF CROP DIVERSITY

Miller shared some data from a study done at Dakota Lakes on crop diversity that showed continuous corn results in a 190-200 per acre long-term bushel average. Rotating corn and soybeans yielded 217 bushels per acre on average.

“The first corn in this corn/corn/soybean/wheat/soybean rotation yielded 256 bushels per acre,” Miller says. “The second year, corn yielded 213 bushels per acre.”

When winter wheat was drilled in as a cover crop, the soybean yield increased by 7.3 bushels per acre to 63 bushels per acre in a corn-soybean rotation.

“Where we didn’t have a cover crop, the soybeans yielded 55-56 bushels per acre,” Miller says. “The first year we planted a more diverse crop rotation after a longer break, we yielded 76 bushels per acre with no cover crop. The second year planting soybeans after wheat under irrigation with a big cover crop yielded 81 bushels per acre.”

In an ideal world, Miller recommends planting the opposite type of cover crop to the cash crop the following year to help protect against disease and insects.

“Some growers in Nebraska have had trouble with wheat stem maggot when they plant green corn into cereal rye,” Miller says. “That’s a grass going to a grass. I don’t like that. You can have a little bit in there, but not a lot.”

“Wheat can easily add diversity to a crop rotation,” Miller says.

“Wheat is a cool season grass. Corn is a warm season grass, and soybeans are a warm season broadleaf,” Miller says. “We’re missing cool season broadleaf, so we need some of those in there. In a corn/soybean rotation, we’re missing both the cool season grass and broadleaf.”

Miller says the benefits of cover crops accrue over several years, and growers will see improvements in yields, pest management, and soil tilth if there is a strong commitment to cover crops.