Roller Crimper

A mechanical implement that terminates cover crops by crushing and creasing stems, leaving a flat mulch on the soil surface without tillage. An increasingly important tool for reducing herbicide use in CA and organic systems.

How It Works

A roller crimper kills cover crop plants by physically injuring stem tissue — bruising or creasing the plant so severely that it cannot recover. Unlike mowing or mulching, the crimper does not touch the ground and leaves the terminated biomass on the surface intact.

Why intact biomass matters:

  • Maintains soil cover against heavy rain, erosion, and evaporation
  • Reduces temperature extremes at the soil surface
  • Less nitrogen hunger for the following crop — biomass decomposes from above, so N is not immediately tied up in soil incorporation (unlike mulching)

The technique was pioneered in South America, developed extensively in organic systems, and has spread to conservation agriculture and conventional farming worldwide.

Conditions for Effective Use

1. Crop Development Stage

Rolling is generally only effective on well-developed vegetation. The critical threshold is after flowering:

“After flowering, the plants are a lot more susceptible to this physical mode of destruction because the plant reserves are then redirected towards reproduction rather than vegetative growth.”

  • For overwintered cover crops: late sowing dates are acceptable given long growing periods
  • For short-term covers before cereals: very early sowing dates are essential to allow covers to reach appropriate stage

2. Frost

Frost dramatically improves effectiveness:

  • Cold damages plant tissues, making them more susceptible to crushing
  • Rolling during a frost recommended for species that would otherwise survive a normal winter
  • Frozen ground required to avoid physical damage to soil structure by heavy machinery
  • Well-covered soil tends not to freeze hard (biomass acts as buffer)

3. Roller Type

A simple flat roller is significantly less effective than a purpose-designed crimper:

Roller Type Effectiveness Notes
Flat roller Limited Can work on white frost; least reliable
Cambridge/packer roller Moderate Better than flat; still limited in tough conditions
Cross-kill or bar crimper Good Significantly more reliable across a range of conditions
Purpose-built blade crimper Best Large diameter + helical blade arrangement + adjustable ballast

Key design features of effective crimpers:

  • Large diameter — operates at higher forward speed with fewer revolutions; more blades per circumference means less “jumping” and more even pressure
  • Adjustable ballast — water or sand can be added according to weather and canopy toughness (tractor weights or dual ballasted wheels serve the same purpose)
  • Blade angle — reducing angle sufficient to damage stems; increasing angle for woody stems; excessive angle + low biomass may produce variable results
  • Helical or offset blade arrangement — perpendicular mounting promotes vibration and uneven pressure distribution; helical mounting solves this problem

Species Susceptibility

Different species and varieties vary considerably in susceptibility:

Easily destroyed by rolling:

  • Mustard (green, before stem hardens)
  • Crimson clover
  • Field bean
  • Rye (at flowering stage with blade crimper — before flowering, rolling a cereal enhances tillering!)
  • Tillage radish
  • Tall vertical species generally

Resistant / difficult to destroy by rolling alone:

  • Perennial species (red clover, alfalfa) — underground architecture protected
  • Turnip, rapeseed (stem hardened, underground architecture protected by frost)
  • Mature/lignified cereal stems
  • Established broadleaved weeds, mustard (post-flowering, hardened stem)

“The choice of variety within plant species is essential: choose covers that will reach the appropriate stage at the date of destruction required — neither too advanced (risk of running to seed) nor too immature (difficult to destroy by rolling).”

Important distinction for cereals:

  • Rolling a young cereal enhances tillering (conventional or cambridge roller)
  • Rolling a cereal at flowering with a blade crimper kills it — exhausts the plant trying to feed damaged tillers
  • Cutting (silage or grazing) triggers secondary tiller production; crimping does not

Combined Rolling + Herbicide

French research (Labreuche/Arvalis, 2009–2011) tested rolling combined with reduced-dose glyphosate:

Key findings:

  • Rolling before herbicide application: most effective on sensitive species (cereals, oats, lentils) — consistent results
  • Sensitive species: improved destruction by 95% for crimson clover, 99% for cruciferous plants after rolling + reduced herbicide
  • Volunteer rapeseed: Rolling + 360g/ha glyphosate as effective as 720g/ha without rolling (saves 1 litre/ha of product)
  • For broadleaf weeds: effectiveness improved by 40%

Critical timing: Spray within 2 hours of rolling for maximum effect:

  • Injuries from rolling improve penetration of herbicide
  • Delay of 24 hours reduces effectiveness by 10–15%
  • Delay of 15 days: almost zero additional effect (plant has healed)

Note: For 360g/ha on rapeseed, adding 480g/ha of 2,4-D is more effective (70%) than rolling alone (40%).

Rolling cost (Arvalis data): €12/ha, 3 litres/ha fuel, 20 minutes/ha for 6m Cambridge roller.

Beyond Termination: Selective Weed Management

The crimper can also be used as a selective weed management tool — not just for total canopy destruction:

  • Selective suppression: tall vertical species (mature cereals) destroyed; low-growing species underneath (rape, clover, alfalfa) retained
  • Weakening of flowering perennials (thistles, docks) in fallow without mowing — prevents stem regrowth
  • Localised weeding between rows with crimper instead of coulter weeder — maintains cover crop as mulch without touching ground
  • “Roll-sow-apply total herbicide” technique: extend growing period right to sowing date, particularly for autumn sowing

Practical Considerations

“Before rushing to purchase a purpose built machine it’s worth exploring what is already in your yard.”

  • A cambridge roller can work on white frost conditions — a reasonable starting point
  • Two passes with a simpler roller may substitute for one pass with a purpose-built crimper in borderline conditions
  • Second pass, or complementary reduced-dose herbicide, available as back-up if first pass insufficient

Sources

  • [[sources/dd-issue-02]] — “Rolling Cover Crops: A Rich Technique of Opportunities with Much Still to Master”, Matthieu Archambeaud, TCS Magazine No. 64 (Sept/Oct 2011); Labreuche/Arvalis trial data (2009–2011), reproduced in Direct Driller Issue 2 (June 2018)

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