MADISON, Wis. – We’re learning that working with cover crops in a northern climate presents some unique challenges. The short cash crop growing season makes it difficult to find adequate planting windows that allow for timely planting and sufficient growth of cover crops.
Researchers are constantly looking for and developing ways to overcome these challenges and find new ways to incorporate cover crops into row crop rotations. One such method is the roller-crimper – a cover crop termination tool which provides a management tool to help farmers reap the benefits of cover crops throughout the entire production system.
“The roller-crimper is a way for farmers to intensify their use of cover crops within their cash grain rotation with all the benefits that high biomass cover crops bring to the soil,” said Dr. Erin Silva of the University of Wisconsin-Madison, during a recent phone interview. “Additionally, it allows a way to reduce the need for cultivation for weed management, particularly in organic production systems.”
A cover crop like winter cereal rye is planted in the fall following harvest, typically following a shorter season crop like corn silage or small grain. Farmers and researchers are also experimenting to see if the cover crops could be inter-seeded into grain corn, allowing for the earlier cover crop planting dates that allow for the cereal grain to germinate and establish prior to winter.
“It goes dormant through the winter, but still leaves that nice living cover on the soil even under the blanket of snow, then, starts growing again in April, once the weather warms up,” she said.
All through winter, even though the crop is dormant, there is still a living root in the soil. These living roots can benefit the biology in the soil as it begins to warm in the spring. Even though the soil is cold, the biology have not shut down completely, and are waiting to begin metabolizing and breaking down crop residues in the spring when conditions are right.
In the spring, the cover crop is growing again and producing the biomass that allows it to become an effective weed management tool.
“The roller-crimper, which is essentially a big cylinder upon which blades are welded, when that roller-crimper comes over the cover crop to mechanically terminate the cover crop, right when the cover crop is flowering, that high amount of biomass leaves a thick mat on the soil surface,” she said.
Timing is crucial with the roller-crimper. If mechanical termination is the only method used for terminating the cover crop, the plants should be at the flowering stage where pollen is visibly falling from the flower when the roller-crimper is used. At this stage of cereal grain maturity, the cover crop will form a killed mulch after roller-crimping due to the simultaneous crushing and snapping of the plant.
The resulting mat of biomass acts like straw would in a garden or mulch in a flower bed.
“By blocking the sunlight from reaching the soil surface, we are essentially preventing or inhibiting weeds from establishing,” she said. “All the weed management for the cash crop comes by having that thick mat of cover crop residue on the soil surface.”
This is beneficial to organic growers, but also to growers that are facing heavy populations of herbicide resistant weeds in their fields.
This method of cover cropping may help growers reduce their need for herbicide applications.
“That is an area honestly where there has been more limited research, but I think certainly an area that warrants more research as well,” said Silva. “Farmers are interested in ways to facilitate and enhance their soil health and also looking for additional tools as we see herbicide resistant weeds start to emerge.”
It is still unclear how this method of cover cropping and terminating the crop with the roller-crimper will fit into weed management, particularly herbicide resistant weeds, but it is another tool for farmers to consider.
Winter annual cereal rye tends to work best as a cover crop for this method. It establishes easily, grows well and is terminated by the roller-crimper when rolled at the right time.
While there are a few legume cover crops that can be terminated with the roller-crimper, it has been difficult to find a variety that survives the winter well enough to be reliable.
It also best to plant soybeans as the next crop going into the cereal rye. Soybeans can be planted late enough that the rye develops adequate biomass without an impact on the soybean’s yield.
“In the middle Atlantic region, in North Carolina, they are able to do this with corn into a legume cover crop using the same principles,” she said. “But here in the upper Midwest, our growing season for corn is just too short as well as that initial spring growing season to get that cover crop biomass produced.”