Limiting horizons

1
Limiting horizons

• Basic Soils Training
• 3/06

2
Root-limiting

• Fine roots can penetrate in a few vertical
  cracks, but those cracks are spaced on average 10
  cm or more apart.
• Coarse woody roots are not an indicator.

3
Types of root-limiting horizons

• Soil material
• Btx or Bx - Fragipan (dense, noncemented, often
  has calico colors and vertical ribbons around
  darker missles)
• Cd - densic layer (dense, structureless)
• Bhm - orstein (cemented spodic)
• Bv - if the plinthite is horizontal (called
  ironstone)
• Bedrock
• Cr - weakly to moderately cemented bedrock
• R - strongly cemented bedrock

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Water-limiting

• The horizon or layer restricts water conductivity
  so much and long enough that redoximorphic
  features (no matter how faint) form in the
  horizon or right above it.
• The redox features must be current and not a
  color pattern from primary rock weathering
  (lithochromic).

5
Types of water-limiting horizons(must have gray
redox in or above!)

• Cr or Cr - flat-lying, thin-layered bedrock
• Bt, BC, or C - horizons with platy structure
• Bt, BC, or C - clayey texture with high density
• Bt, BC, or C - clayey texture with none to
  moderate structure
• Bt, BC, or C - silty-clay loams and clay loams
  with none or weak structure