While it might be tempting to skip the process of planting a cover crop, there are some very compelling reasons not to.
Aaron Bowman, an agronomist with PRIDE Seeds says cover crops can reduce the soil erosion caused by wind and rain, as well as alleviate soil compaction.
As well, Bowman says cover crops aid in weed suppression, pest reduction and also help sequester carbon, which improves soil health.
“After the cash crop has been removed, cover crops help nourish the soil biology,” he says. “They help bridge the gap between harvest and planting and give the soil a continued energy source.”
Once the decision has been made to plant a cover crop, there are several things to consider.
Will the grower be planting a single cover crop (monoculture) or a mixture (polyculture)?
Bowman says it really comes down to what best meets the needs of the producer and the soil.
“Different cover crop’s root structures or growing habits lend themselves to different goals,” says Bowman.
A basic rule of thumb is to select a cover crop from each group: legumes, warm season grass, cool season grass and brassica family.
“By selecting one of each, you spread your risk as well as take advantage of the varying benefits of each group,” says Bowman, pointing to a few examples:
TILLAGE RADISH
• Alleviates compaction
• Nitrogen scavenger
• Suppresses weeds
• Does not over-winter
CEREAL RYE
• Fibrous root structure provides amazing erosion control
• Over-winters
• Nutrient scavenger
• Suppresses weeds
• Produces large amounts of biomass in the spring
OATS
• Great nitrogen scavenger
• Winter kills
• Lends itself to grazing/harvest for livestock
PEAS
• Many varieties available, with varying winter hardiness
• Fixes nitrogen
• Works well in a mixture of grasses
• Makes great feed or late season pasture
• Produces large amounts of biomass if planted early enough.
Bowman says, “it’s also very important to know whether the cover crop is frost sensitive and to know your own area’s frost-free date.”
Crops like buckwheat, sunflowers and phacelia are more frost-sensitive that some others so Bowman advises caution if planting later, after corn silage for example.
The carbon to nitrogen ratio of the mix is also an important factor.
“As the C:N ratio increases, the release of nitrogen to the subsequent cash crop is hindered,” he says. “If the C:N ratio gets too high, the soil will have to provide nitrogen to break down the extra carbon in the mix.”
While that might be a challenge in the short-term, Bowman says that long-term it will help sequester carbon in the soil as well as build organic matter, which, “should be a long-term goal of every producer.”
When it comes to his own operation, Bowman says he prefers a carbon to nitrogen ratio of 20:1, but acknowledges that other producers and researchers prefer a 10:1 ratio.
“It all depends what the next crop is and my goals,” he says.
