Add Cover Crops Between Wheat to Jump-Start Soil Health
The 100 days between winter wheat harvest and winter wheat planting are a fine time to grow short-season cover crop blends, according to Windom, Kansas, farmer Joe Swanson. The practice offers a double dose of benefits by jump-starting soil biology and suppressing weeds.
“I’d rather put $15 worth of cover crop seed in the ground than apply herbicide,” Swanson says. “With cover crops, I feed the biology and have nutrient transfer to help the following wheat crop.”
Abbey Wick agrees. “That is a nice chunk of growing period,” says Wick, who is Extension soil health specialist at North Dakota State University. “There are a lot of opportunities to fit a cover crop in that time span. One hundred days is an incredible amount of time to keep the soils functioning.”
In winter wheat country, there are usually 12 to 14 weeks of fallow between harvest and planting. Planting cover crops during this time is dicey. Typically, if you are planting another wheat crop into that wheat stubble, you let the land store moisture knowing you’ll need to kill weeds at least one time and often twice before wheat planting commences. Swanson, however, prefers to let cover crops do the work.
As soon after the combine as possible, Swanson plants a mix of cover crop species that includes buckwheat, German millet, sunn hemp, rapeseed, and sunflowers. The mix varies depending on what he is trying to accomplish. To break the green bridge of grass species that can promote disease and insect infestation, Wick suggests a cover crop mix of broadleaves and brassicas. Roots from these crops – especially brassicas like radish and turnip – can reach down 4 feet within 60 days, breaking up compaction layers. The tubers of these crops also serve as a storehouse for residual nitrogen.
“Brassicas increase the efficiency of the nutrient cycle,” she says.
When the nitrogen becomes available for a cash crop depends upon the region, but it’s generally within a year.
Weed Suppression Benefits
Swanson believes growing a blend of cover crops in between winter wheat crops keeps summer weeds at bay.
“Last year, I had wheat stubble without a cover and fought Palmer amaranth,” he says. “That’s why I’m thinking if I get a good, thick stand that shades the ground, it might save a pass with a sprayer. Then, I think the cost of a cover crop is basically a wash.
“The other thing is, I’m doing my soil a lot more good with a cover crop blend than running the sprayer over it,” he adds.
Wick says the main benefit of cover crops in this time frame is erosion control. “If you have cover, the soil stays in place.”
When to Terminate
Swanson advocates a relatively short growing season for the cover crops. He applies a herbicide application no later than six weeks after they begin growing.
“I spray then because I want to get them knocked down before they create hard residue,” Swanson explains. “I want to have a short carbon-to-nitrogen ratio. I don’t want it to head out or have a hollow stem.”
Determining when to kill the cover crops is not easy.
“I recommend that you terminate the crops when you’re comfortable,” Wick says. “There are pros and cons to early or late termination, but it’s hard to argue with a gut feeling.”