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Chromosols [CH]


Soils with strong texture contrast between A horizons and B horizons. The latter are not strongly acid and are not sodic. The soils of this order are among the most widespread soils used for agriculture in Australia, particularly those with red subsoils.

Distribution of Chromosols in Australia.
Soil Profile (View type example photo of Brown Chromosol).


Soils other than Hydrosols with a clear or abrupt textural B horizon and in which the major part of the upper 0.2 m of the B2 horizon (or the major part of the entire B2 horizon if it is less than 0.2 m thick) is not sodic and not strongly acid. Soils with strongly subplastic upper B2 horizons are also included even if they are sodic.


In the case of those soils with strongly subplastic B horizons, care needs to be taken to ensure if they qualify for the clear or abrupt textural B horizon. As far as is presently known, such soils appear to be largely confined to the Riverine Plain of south eastern Australia.



The Red and Brown suborders account for 80% of the profiles classified.

Great Groups

These will vary somewhat among the various colour class suborders, but it is likely that the subdivision given below will apply to most.


The calcareous classes above approximately correspond to those of Wetherby and Oades (1975) as follows: Hypocalcic - Class IV, Lithocalcic - Class III B and IIIC, Supracalcic - Class III B, Hypercalcic - Class III A, Calcic - Class 1 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 Calcic class was found to be most common in soils with a calcareous horizon. However, almost half of the Chromosol great groups classified were Eutrophic. 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.


The subgroups listed below may not all be relevant for every great group of every suborder.


Forty percent of the profiles classified so far have a Haplic subgroup. This would suggest that the class may need to be further subdivided, but it is difficult to find suitable criteria to base this on. The presence of a pale (unbleached) A2 horizon could be used, but the significance of this is uncertain. A subdivision could be made between soils with clear or abrupt textural changes if this was thought to be of importance. Similarly, a distinction between structured and massive B2 horizons could be made. Possible changes such as these can easily be introduced if evidence is produced to justify their use.

Family Criteria

A 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)

B horizon maximum texture1

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 This refers to the most clayey field texture category.

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