When it comes to choosing the right cover crops for your farm, one size definitely doesn’t fit all.
“Growers need to have an objective in mind in terms of what they want to get out of a cover crop,” said Bob Blackshaw, a research scientist with Agriculture and Agri-Food Canada.
“You have to choose the cover crop that will address what you hope to improve on your farm.”
Cover crops improve farmland and that allows producers to “make more money in subsequent years,” said Blackshaw.
Depending on the species, cover crops can prevent soil erosion, improve soil quality, reduce soil compaction, fix nitrogen, and suppress weeds.
The first step to picking the right cover crops is to choose plants from “the four different categories — warm-season broadleaf and grasses, and cool-season broadleaf and grasses,” said Nora Paulovich, manager of Northern Peace Applied Research Association.
That level of diversity brings in different benefits for the land, including a variety of rooting systems and nutrients for the soil, said Paulovich.
“We used to think that every plant you put in there was competing with other plants for moisture and nutrients,” she said.
“But we’re really seeing now that with the diversity of roots, you’re really increasing the diversity of the microflora in the soil, and there really is a synergistic effect.”
That’s why Kevin Elmy blends up to 20 different species of cover crops on his farm near Saltcoats, Sask.
“In a monoculture, you’ve got the roots growing at the same speed, same direction, same depth, and competing for the same nutrients and moisture,” said Elmy, who has been growing cover crops for six years.
“When you grow a polyculture, you’re not competing for all the same nutrients.”
The right tool
Choosing the right species to add to the blend “really depends on the type of goals that the producer has,” said Elmy.
If soil nitrogen is an issue, for instance, legumes are a must-have.
“If a person’s looking at fixing nitrogen, we can use things like sun hemp, crimson clover, red clover, and annual alfalfas,” said Elmy, adding that soybeans, faba beans, chickpeas, peas, and lentils are other options.
Crops that provide a lot of cover — like grasses and legumes — can help prevent soil erosion, and “scavengers” like hybrid brassicas, turnips, radishes, and buckwheat are “really good” at drawing nutrients out of the soil for other crops. For salinity issues, Elmy recommends fall rye, barley, sunflower, sugar beets, and safflower.
Cover crops can also be used to combat drought by increasing the soil’s water infiltration and water-holding capacity, he said.
“If that’s your main goal, the way you’re going to get to it is by increasing organic matter and breaking up that hardpan,” said Elmy.
To build organic matter in the soil, pick species with higher root biomass, he said.
“That will be a lot of your grasses — oats, triticale, annual ryegrass, sorghum, corn.”
For breaking up hardpan, tillage radish is his go-to cover crop.
“You want to include some deep-rooted species like chicory and tillage radish so you’ve got some roots that are going to chip away at the hardpan,” he said.
“The roots will exert 290 psi and will break up the hardpan, and once it goes through that hardpan, it’s going to keep drilling down. They’ll go down past where the normal annual cropping roots will go and get the nutrients those crops can’t get.”
Creating the right blend involves “a lot of research” and trial and error, said Elmy, who uses two different blends on his own farm.
“We bring in different species from around the world — India, South Africa, United States — to get enough diversity of warm- and cool-season grasses, broad leaves, and legumes, and then we have to see how they adapt when they’re grown here,” he said.
“This year, I’m bringing in eight new crops for trials. The only way we’re going to know how they work is by putting them in the ground, doing some blends, and getting some experience with them.”