Rolling and crimping of cover crops is a crucial component to making organic no-tilling work, experts say.
Biomass left over from a healthy canopy of cover crops can suppress weeds, while roller-crimpers handle cover crop termination — all without the use of herbicides or tillage.
But ensuring that the cover crop grows enough biomass to suppress weeds and is completely killed requires dedicated management.
“I’ve gotten a lot of calls over the years from organic farmers who were disappointed in the result in weed control with covers,” says Holtwood, Pa., no-tiller Steve Groff, who has been roller-crimping since 1995. “And, even sometimes in the ability of the crimper to terminate it.”
Groff warns this system can be a little unreliable, as he estimates 1 out of 5 years will be poor, 1 will be excellent, and the other 3 will be decent. But following some guidelines can increase the chances of success.
1. Seed Earlier, Heavier
Succeeding with roller-crimping starts the year before, at cover crop seeding. Because organic no-tillers are relying on covers to control weeds, it’s important to select species that will survive into the following spring and to seed them at a higher rate to provide adequate ground coverage.
Cereal rye is the most popular species for this and the one University of Wisconsin-Madison assistant professor Erin Silva recommends to organic no-tillers. Silva leads the university’s Organic and Sustainable Agriculture Research and Extension program and has been researching how to succeed with organic no-tilled soybeans.
The reason cereal rye is the top choice, she says, is due to its winter hardiness, ability to mature earlier than other cereal grains and its effectiveness in suppressing weeds.
For a seeding rate, Silva recommends no-tillers start at 3 bushels per acre.
“That is quite a bit higher than the typical bushel or bushel-and-a-half you’d typically use for a cover crop,” she says. “But this is the keystone of your weed management program, so you’ll want to make that extra investment to get that biomass quantity you’re looking for.”
The goal is to achieve at least 8,000 pounds of biomass per acre, she says.
Groff agrees no-tillers should seed cereal grains heavier in this system but recommends adjusting the rate based on the seeding date and fertility plans. He suggests no-tillers start with 1½ bushels when seeding in September, 2 bushels in October and 3 bushels in November, then adjust higher or lower for nutrient management.
If a no-tiller plans on spreading manure in the fall, he says the rye will be even thicker and will fall down if the seeding rate is too high.
But Silva points out that in northern areas, seeding past September will be too late to achieve the biomass necessary for weed suppression. For growers in these regions, this may mean planting earlier corn hybrids and soybean varieties to get the cereal rye seeded earlier or incorporating a grain like winter wheat or oats into the cash crop rotation, since their harvest is earlier in the year.
2. Choose the Right Tool
The next factor in succeeding with a roller-crimper is the tool itself. While there are a variety of shapes, sizes and styles of roller-crimpers available on the market, Groff says they can all get the job done.
“If you have a roller-crimper that was designed to roll cover crops, they’re similar enough to say there’s not one that’s better than another,” he says.
But there are some factors no-tillers should consider when choosing one for their operation — one of which is whether their fields have a lot of contours.
Cover Crop Species to Use and Avoid with Roller-Crimpers
- Annual Ryegrass: The stems don’t lend themselves well to roller-crimping.
- Dwarf Essex Rape: It can’t be terminated with a roller-crimper alone.
- Sorghum-Sudangrass: It fights termination and tends to grow back after roller-crimping.
- Cereal Rye: It’s great for weed suppression and can be terminated with a roller-crimper. Consider the variety Aroostook, as it’s marketed for roller-crimping because it can reach the flowering stage about 10 days earlier than other varieties.
- Clovers: Crimson clover doesn’t terminate as easily as hairy vetch, but it can be used. The stem of balansa clover is pinky-sized and hollow, so the roller-crimper has no problem terminating it.
- Hairy Vetch: Its succulent and tender stems make it easy to terminate with the roller-crimper. It needs to reach 100% bloom to be terminated. Pairs well with triticale because they tend to mature very close together. However, it tends to pull down other species it’s with, so no-tillers may need to roll twice if they suspect lodging may occur.
- Sunn Hemp or Buckwheat
- Triticale: It can achieve adequate biomass and improved varieties are more winter hardy and less likely to lodge due to its thicker stem.
- Wheat or Barley: Both tend to mature fairly early, which means they can be roller-crimped earlier.
- Winter peas: They’re succulent, so they’re easy to terminate.
This is important because a bigger roller-crimper on undulating terrain won’t effectively roll parts of the field where the soil may be a couple inches lower.
In this case, it might be best to use a roller-crimper that consists of smaller sections. For example, the 10-foot roller-crimper Groff developed for his farm has 22-inch sections — four in the front and four in back — with the front rank overlapping the back. The sections can also flex, so they’re able to crimp every part of the field consistently.
Another option is a tool like Underground Agriculture’s ZRX roller, which attaches to planters and fits one roller-crimper per row. This will follow the contours of the field better and eliminate an additional pass in the field, which can reduce compaction while saving time, labor, machine wear and tear, and fossil fuel emissions, says Silva. However, it can make the option of roller-crimping before planting more challenging.
“The seeding rate is the keystone of your weed management program, so you’ll want to make that extra investment to get the biomass quantity you’re looking for…” – Erin Silva
Rolling a second time may be necessary if the roller-crimper wasn’t aggressive enough on the first pass, so having the ability to add weight or down pressure is a feature you may wish to consider.
If a no-tiller opts for a roller-crimper separate from the planter, they’ll need to decide whether to put it in front of or behind the planter. The Rodale Institute suggests farmers run their roller-crimper in front because they discovered when they rolled it behind, it wasn’t able to effectively terminate the cover crop that was in the tractor tracks. But Groff says that’s a result of tillage.
“They had planted their cover crop in tilled ground, so in the spring when they went in and rolled it, their tractor tracks made an indentation in the soil and it didn’t really crimp the cover crop in the tracks,” Groff says. “In a good no-till situation, you won’t leave tractor tracks, so you don’t need to put it on front.”
Tractor horsepower is another consideration. Groff says the heavier the roller-crimper, the more horsepower you’ll need to lift it up.
As a general guideline, 100 horsepower is preferred for the 10-foot, 2,500-pound roller-crimper that Groff has, but he says no-tillers should work with their equipment dealer to match the right tractor to a roller-crimper.
3. Roll at the Right Time
One of the big challenges is deciding when to terminate the cover crop, and it depends on what cover crop species are growing and their stage of maturity.
With cereal grain crops, Silva says they need to be roller-crimped at the end of anthesis, when anthers are hanging from the tip and bottom of the grain heads and yellow pollen is shedding. If the anthers are hanging from the center of the heads, it’s too early. After roller-crimping, the cover crop should lie on the ground as a flat mat — not spring back up and continue to grow, she notes.
Broadleaves and legumes need to reach full bloom or early pod set, she says.
Because cover crop termination has to occur later than it would in a conventional system, organic no-tillers may need to plant cash crops into the cover crop before rolling or select a shorter-season cover crop species so it will reach maturity earlier.
It’s possible to plant soybeans into cereal rye at the boot stage and then roller-crimp the rye at anthesis, which is around the V2-V3 stage for soybeans. This allows soybeans to be planted 2-3 weeks earlier, rather than waiting until after the rye has been rolled and crimped.
Silva says the roller-crimper doesn’t significantly damage the soybeans at that stage. If the soybeans are too early in maturity — before V1 — then the roller-crimper may hurt the stand.
4. Roll Twice to Prevent Lodging
The biggest challenge Groff faces with roller-crimping is when a wind or storm event causes his cover crop to lodge. This often results in the stems of the cover crop lying across the ground in every which way, making it difficult for his planter to cut through the cover and achieve good seed-to-soil contact. Hairpinning may also occur.
He adds that lodging is also more likely to happen in organic no-till systems because of the thicker cover crop seeding rate. The thicker the stand, he says, the increased potential for it to lodge.
AVOID LODGING. Having a cover crop lodge can result in stems lying in different directions, which can make planting more of a challenge. To avoid this, no-tiller Steve Groff will often roller-crimp his cover crop before a rain or wind event so that the stems will be parallel to his rows. He’ll come back later with the roller-crimper when it’s time to terminate the cover crop.
Because of this, Groff recommends organic no-tillers plan on rolling their cover crop twice, which will not only prevent lodging but also help completely terminate the cover crop.
While Groff is not in organic production, this is a strategy he’s used on his own farm. One year Groff roller-crimped crimson clover when it was around 30-40% flowered, about 3 weeks before planting, because heavy rain was expected and he knew the cover would go down.
“It doesn’t stop growing,” he says. “I’ll still get the benefits over the next 3 weeks, but my main stems are going to be lined up parallel to planting.”
To terminate the cover crop, Groff says no-tillers will need to roller-crimp again over the cover crop at the time they would have if the cover was still standing.
Groff notes that lodging isn’t as much of a concern with succulent legumes like crimson clover and hairy vetch because they’re much easier to cut through than a species like cereal rye or triticale.
Determining when to make that first pass with the roller-crimper depends on the cover crop stand, Groff says, explaining that growers will eventually have a gut feel for the right time as they continue this practice over time.
Until that intuition is there, Groff says growers should err on the side of being proactive against lodging. “It doesn’t cost much to roll and lodging is difficult to overcome. It’s difficult to plant through it.”
5. Be Flexible
The final piece of advice Silva and Groff offer is to stay flexible and understand that roller-crimping is not a perfect system.
“If the cover crop looks less than ideal in the spring — if it looks skimpy, or you got it in too late, or had a lot of winterkill — just be ready for a plan B,” Silva says. “Don’t get too locked into the mindset of roller-crimping and terminating mechanically no matter what.”
Groff and Silva encourage no-tillers to start small — preferably no more than 10-20 acres in the beginning, Silva says. Groff adds no-tillers need to learn the limitations of the practice before expanding, while staying nimble and being prepared to make decisions on a field-by-field basis.
“There is no exact prescription,” he says. “Success is a summary of many little management decisions.”