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Dermosols [DE]

Concept

Soils with structured B2 horizons and lacking strong texture contrast between A and B horizons. Although there is some diversity within the order, it brings together a range of soils with some important properties in common.

map
Distribution of Dermosols in Australia.
Soil Profile (View type example photo of Red Dermosol).

Definition

Soils other than Vertosols, Hydrosols, Calcarosols and Ferrosols which:

  1. Have B2 horizons with structure more developed than weak1 throughout the major part of the horizon, and
  2. Do not have clear or abrupt textural B horizons.

Comment

Some clayey soils in the arid zone which are relatively high in salt tend to have strong, fine blocky structure. It may be difficult to decide if they are Vertosols or Dermosols because of an apparent lack of cracking and slickensides or lenticular structure. The use of shrinkage measurements such as those discussed under vertic properties will help to resolve this situation.

Suborders

  • The dominant colour class in the major part of the upper 0.5 m of the B2 horizon (or the major part of the entire B2 horizon if it is less than 0.5 m thick) is red.
    • Red [AA]
  • The dominant colour class is brown.
    • Brown [AB]
  • The dominant colour class is yellow.
    • Yellow [AC]
  • The dominant colour class is grey.
    • Grey [AD]
  • The dominant colour class is black.
    • Black [AE]

Comment

The upper 0.5 m of the B2 horizon is used as the diagnostic section for colour in Dermosols, Ferrosols and Kandosols because of the often indistinct A-B horizon boundaries in these soils compared with those in Chromosols, Kurosols and Sodosols. Of the Dermosols classified, 73% were Red or Brown in the upper B2 horizon.

Great Groups

It is thought that the great group classes listed below will be appropriate for most of the various colour suborders, although yellow and grey forms are relatively uncommon.

  • Soils with a red-brown hardpan either within or directly underlying the B horizon.
    • Duric [BJ]
  • Soils with a B horizon either containing or directly underlain by ferricrete, a petroferric horizon, or a petroreticulite horizon.
    • Petroferric [EA]
  • Soils with a B horizon that is not calcareous and which directly overlies a calcrete pan.
    • Petrocalcic [DZ]
  • Soils in which the upper 0.2 m of the B2 horizon (or the B2 horizon if it is less than 0.2 m thick) has a strong blocky or polyhedral structure in which average ped size is usually in the range of 5-20 mm. There is very weak adhesion between peds (when dry it is very easy to insert a spade into the upper B2 horizon). Salt contents are usually high, resulting in weak dry strength and a bulk density of about 1.3 t m-3 less. In some soils the B2 horizons may be weakly subplastic. A common feature (but not diagnostic) of the overlying A horizons is the presence of a band of vesicular pores near the surface or on the underside of any surface flake.
    • Pedaric [BK]
  • Soils in which the major part of the B2 horizon is strongly subplastic.
    • Subplastic [ET]
  • Soils with an exchangeable Ca/Mg ratio of less than 0.1 in the major part of the B2 horizon.
    • Magnesic [DB]
  • Soils in which the major part of the B2 horizon is dystrophic.
    • Dystrophic [AF]
  • Soils in which the major part of the B2 horizon is mesotrophic.
    • Mesotrophic [AG]
  • Soils in which the major part of the B2 horizon is eutrophic but the B and BC horizons are not calcareous.
    • Eutrophic [AH]
  • Soils in which the carbonate is evident only as a slight to moderate effervescence (1 M HCl), and/or contain less than 2% soft finely divided carbonate, and have less than 20% hard carbonate nodules or concretions.
    • Hypocalcic [CV]
  • Soils with a calcareous horizon containing more than 50% of hard calcrete fragments and/or carbonate nodules or concretions and/or carbonate-coated gravel.
    • Lithocalcic [DA]
  • Soils with a calcareous horizon containing 20-50% of hard calcrete fragments and/or carbonate nodules or concretions and/or carbonate-coated gravel.
    • Supracalcic [FB]
  • Soils with a calcareous horizon containing more than 20% of mainly soft, finely divided carbonate, and 0-20% of hard calcrete fragments and/or carbonate nodules or concretions, and/or carbonate-coated gravel.
    • Hypercalcic [CQ]
  • Other soils with a calcareous horizon. (See carbonate classes).
    • Calcic [BD]

Comment

The calcareous classes above approximately correspond to those of Wetherby and Oades (1975) as follows: Hypocalcic - Class IV, Lithocalcic - Class III B and III C, Supracalcic - Class III B, Hypercalcic - Class III A, Calcic - Class I and IIIA. In the Lithocalcic and Supracalcic classes the coarse fragments may be >0.2 m in size and soft carbonate may or may not be present.

Of the profiles classified, the Eutrophic class (40%) was the most common great group. The Duric and Pedaric soils are virtually confined to the arid zone, the former being particularly widespread in Western Australia and the latter in western Queensland and New South Wales, and in South Australia.

Subgroups

It is thought that the following subgroups will cater for most situations, although obviously some will not be relevant for particular great groups.

  • Soils with a humose horizon and the major part of the B2 horizon is mottled.
    • Humose-Mottled [CM]
  • Soils with a humose horizon and the major part of the B2 horizon is strongly acid.
    • Humose-Acidic [GY]
  • Other soils with a humose horizon.
    • Humose [CK]
  • Soils with a melacic horizon and a reticulite horizon which occurs below the B2 horizon.
    • Melacic-Reticulate [GC]
  • Soils with a melacic horizon and the major part of the B2 horizon is mottled.
    • Melacic-Mottled [DI]
  • Other soils with a melacic horizon.
    • Melacic [DG]
  • Soils with a melanic horizon and a B horizon in which at least 0.3m has vertic properties.
    • Melanic-Vertic [DN]
  • Soils with a melanic horizon and the major part of the B2 horizon is mottled.
    • Melanic-Mottled [DM]
  • Soils with a melanic horizon and the major part of the B2 horizon is strongly acid.
    • Melanic-Acidic [FV]
  • Soils with a melanic horizon and a B horizon in which at least the lower part is sodic.
    • Melanic-Sodic [HA]
  • Other soils with a melanic horizon.
    • Melanic [DK]
  • Soils with a conspicuously bleached A2 horizon and a B horizon in which at least 0.3m has vertic properties.
    • Bleached-Vertic [BB]
  • Other soils with a B horizon in which at least 0.3m has vertic properties.
    • Vertic [EX]
  • Soils with a gypsic horizon within the B or BC horizon.
    • Gypsic [BZ]
  • Soils with a ferric horizon within the solum and a B2 horizon in which the major part is strongly acid.
    • Ferric-Acidic [GW]
  • Soils with a ferric horizon within the solum and a B horizon in which at least the lower part is sodic.
    • Ferric-Sodic [HC]
  • Soils with a conspicuously bleached A2 horizon and a ferric horizon within the solum.
    • Bleached-Ferric [AV]
  • Other soils with a ferric horizon within the solum.
    • Ferric [BU]
  • Soils with a manganic horizon within the solum and a B2 horizon in which the major part is strongly acid.
    • Manganic-Acidic [GX]
  • Soils with a conspicuously bleached A2 horizon and a manganic horizon within the solum.
    • Bleached-Manganic [AY]
  • Other soils with a manganic horizon within the solum.
    • Manganic [DC]
  • Soils in which the major part of the B2 horizon is strongly acid and at least the lower part is sodic.
    • Acidic-Sodic [HO]
  • Soils with a conspicuously bleached A2 horizon and a B2 horizon in which the major part is strongly acid.
    • Bleached-Acidic [AU]
  • Soils in which the major part of the B2 horizon is strongly acid and mottled.
    • Acidic-Mottled [AJ]
  • Other soils with a B2 horizon in which the major part is strongly acid.
    • Acidic [AI]
  • Soils with a conspicuously bleached A2 horizon and a B horizon in which at least the lower part is sodic.
    • Bleached-Sodic [BA]
  • Soils in which the major part of the B2 horizon is mottled and at least the lower part of the B horizon is sodic.
    • Mottled-Sodic [HB]
  • Other soils with a B horizon in which at least the lower part is sodic.
    • Sodic [EO]
  • Soils with a conspicuously bleached A2 horizon and the major part of the B2 horizon is mottled.
    • Bleached-Mottled [AZ]
  • Other soils with a conspicuously bleached A2 horizon.
    • Bleached [AT]
  • Soils with a reticulite horizon below the B2 horizon.
    • Reticulate [EF]
  • Other soils in which the major part of the B2 horizon is mottled.
    • Mottled [DQ]
  • Other soils in which the major part of the B2 horizon is whole coloured.
    • Haplic [CD]

Comment

In some dystrophic Dermosols there can be a problem with the definition of Sodic subgroups because of their low base status. (See ESP). No provision is made for Acidic subgroups for soils with melacic horizons as these are most likely to always have acid B2 horizons. Similarly, Acidic subgroups are unlikely to be required for the Dystrophic great groups as most such soils will be acid, whereas the Eutrophic great groups are unlikely to be acid. A number of classes are not mutually exclusive, thus many Vertic subgroups are probably also Sodic or Bleached-Sodic. It is not possible to cater for all such combinations. Of the profiles classified to date, about one third are Haplic, indicating a possible need for further subdivision.

Family Criteria

A1 horizon thickness

Thin [A] : < 0.1 m
Medium [B] : 0.1 - < 0.3 m
Thick [C] : 0.3 - 0.6 m
Very thick [D] : > 0.6 m

Gravel of the surface and A1 horizon

Non-gravelly [E] : < 2%
Slightly gravelly [F] : 2 - < 10%
Gravelly [G] : 10 - < 20%
Moderately gravelly [H] : 20 - 50%
Very gravelly [I] : > 50%

A1 horizon texture

Peaty [J] : See Peaty horizon
Sandy [K] : S-LS-CS (up to 10% clay)
Loamy [L] : SL-L (10-20% clay)
Clay loamy [M] : SCL-CL (20-35% clay)
Silty [N] : ZL-ZCL (25-35% clay and silt 25% or more)
Clayey [O] : LC - MC - HC (greater than 35% clay)

B horizon maximum texture2

Sandy [K] : S-LS-CS (up to 10% clay)
Loamy [L] : SL-L (10-20% clay)
Clay loamy [M] : SCL-CL (20-35% clay)
Silty [N] : ZL-ZCL (25-35% clay and silt 25% or more)
Clayey [O] : LC - MC - HC (greater than 35% clay)

Soil depth

Very shallow [T] : < 0.25 m
Shallow [U] : 0.25 - < 0.5 m
Moderate [V] : 0.5 - < 1.0 m
Deep [W] : 1.0 - < 1.5 m
Very deep [X] : 1.5 - 5 m
Giant [Y] : > 5 m

1 It is common experience that pedologists are inclined to use the phrase 'weak to moderate' when they are in doubt as to the grade of structure. If such a designation is used it will result in the soil being classed as a Dermosol.

2 This refers to the most clayey field texture category.

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