The 12 Soil Orders

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The 12 Soil Orders
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Orders with unique parent materials.
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Andisols (and)

• Volcanic ash soils.

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Histosols (ist)

• Organic soils.

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Vertisols (ert)

• High shrink/swell clay soils.

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Orders formed in unique environments.
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Aridisols (id)

• Arid climates.
• CaCO3 accumulation in subsoil.

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Gelisols (el)

• Colder climates.
• Permafrost layer within 2 m of surface.

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Oxisols (ox)

• Tropics and subtropics.
• Intensely weathered.

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Orders by age.
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Entisols (ent)

• Baby soil.
• Little to no morphological development.

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Inceptisols (ept)

• Toddler soils.
• Weakly developed sub-surface horizons.

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Ultisols (ult)

• Older soils.
• Ultimately weathered.
• Strongly leached.
• Sub-surface clay accumulation.
• lt 35 base sat. in sub-soil.

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Orders developed under unique vegetative
ecosystems.
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Alfisols (alf)

• Forest soils.
• Usually an A-E-B type horizon development.
• The A horizon is usually less than 25 cm.

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Mollisols (oll)

• Grasslands soil.
• Thick, dark A horizon.
• High base saturation.

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Spodosols (od)

• Acid forest soils.
• Usually sandy.
• Thick, bright white E horizon.
• Sub-surface layer of accumulated metal-humus
  complex (Bhs and Bs horizons).

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Summary

• 3 orders with unique parent materials (Andisols,
  Histisols, Vertisols).
• 3 orders with unique environments (Aridisols,
  Gelisols, Oxisols).
• 3 orders by age of development (Entisols,
  Inceptisols, Ultisols).
• 3 orders by unique vegetative influence
  (Alfisols, Mollisols, Spodosols).