Stubble Management and Cutting Height

How harvest stubble height affects the establishment quality of subsequent cover crops. Field trial evidence from Loire-Atlantique, France (2017), conducted on a zero-till and min-till farm of nearly 15 years.

The Experiment

Farm: David Guy’s farm, Loire-Atlantique, France (ET min-till/ZT 15 years) Conditions: Exceptionally dry summer — only 9mm between sowing and first emergence, 8mm in first half of August, 21mm at month end Drill: EasyDrill disc seeder Sown: July 10, 2017, immediately after harvest Indicator species: Mustard, peas, buckwheat (similar reactions seen across other species)

Three stubble treatments compared:

  1. High stubble — cut at 40 cm
  2. Short straw, rolled/shredded — cut at 8 cm, then rolled
  3. Short straw, rolled + shallow stubble cultivation — 5 cm deep cultivation after rolling

Key Findings

Emergence and Early Growth

  • Lowest emergence in rolled short straw (all species) — disc drill hairpins straw into furrow, excluding seed from soil contact
  • High stubble gave best establishment — comparable to no-rolled short straw
  • Differences apparent within 3 weeks of sowing; gap widened through the season

Pea results (3 weeks after sowing):

  • High stubble: ~30 shoots, first tendrils appearing
  • Short stubble: ~24 leaves
  • Rolled straw: ~20 leaves

Buckwheat: High stubble reached flowering stage by late August; others significantly behind.

Mustard biomass (August 28):

  • High stubble: double the biomass of rolled or cultivated treatments
  • Leaf area and growth stage significantly ahead — larger surface, fewer flowers (less stress)

Pea Nitrogen Fixation

Legumes showed the largest response to stubble height — the quality of establishment affects not just biomass but also symbiotic nitrogen fixation capacity:

  • High stubble peas: ~35 kg N fixed
  • Cultivated stubble peas: ~15 kg N fixed

Flea Beetle (CSFB) Impact on Mustard

High stubble provided measurable physical protection against cabbage stem flea beetle:

  • High stubble: only 25% of mustard seedlings attacked
  • Rolled stubble: 68% attacked
  • Cultivated: 85% attacked

This mirrors the companion cropping effect — physical cover that hides or confuses young seedlings from flea beetles (see also Companion Cropping — OSR with Legumes).

Mechanistic Explanations

Why high stubble works better:

  1. Reduced hairpinning — disc drills push straw fragments into the seed furrow, preventing seed-soil contact. High stubble reduces the amount of loose material at ground level
  2. Microclimate buffering — standing stubble reduces wind speed at ground level, which is one of the biggest causes of moisture loss by evaporation in summer
  3. Rain utilisation — in high stubble, even small rain events (8 mm) benefit germinating seeds. Under a flat straw mulch, at least 10 mm is needed to penetrate the straw “blotter” effect
  4. Nitrogen competition — rolled/incorporated straw ties up available surface N during decomposition, starving germinating cover seeds. Legumes suffer particularly as they need a small initial N supply to initiate symbiotic fixation
  5. Temperature moderation — standing stubble moderates surface temperatures; rolled straw can trap heat rather than providing true microclimate benefit in summer

Practical Recommendations

“For successful covers, it is not enough just to have the right drill and concoct the best mixtures; it is necessary to learn everything about managing the straw during the harvest according to the operating conditions.”

  • Leave stubble high (40 cm+) when establishing summer/post-harvest cover crops, especially with disc drills
  • Consider the Shelbourne stripper header — this naturally leaves taller stubble and may be advantageous in zero-till situations
  • Short stubble is not inherently better — it only helps if followed by cultivation, which then triggers fresh weed germination and soil disturbance
  • Nitrogen fertility at sowing matters as much as moisture — covers often suffer more from N deficiency than water stress, contrary to common belief
  • High stubble helps protect early cruciferous covers from CSFB — relevant when interseeding with mustard

Limitations

  • Trial conducted in an unusually dry year, which likely amplified differences
  • Loire-Atlantique climate (warm summers, moderate winters) — conditions in northern UK may produce different relative responses
  • Single-year trial data — patterns confirmed by wider TCS Magazine field experience

Sources

  • [[sources/dd-issue-02]] — “Influence of Cutting Height on Stubble Management”, Frédéric Thomas, TCS Magazine No. 95 (Nov/Dec 2017); trial by Étienne Mignot on David Guy’s farm, Loire-Atlantique

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