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Vertosols [VE]


Clay soils with shrink-swell properties that exhibit strong cracking when dry and at depth have slickensides and/or lenticular structural aggregates. Although many soils exhibit gilgai microrelief, this feature is not used in their definition. Australia has the greatest area and diversity of cracking clay soils of any country in the world.

Distribution of Vertosols in Australia.
Soil Profile (View type example photo of Black Vertosol).


Soils with the following:

  1. A clay field texture or 35% or more clay throughout the solum except for thin, surface crusty horizons 0.03 m or less thick and.
  2. When dry, open cracks occur at some time in most years1. These are at least 5 mm wide and extend upward to the surface or to the base of any plough layer, peaty horizon, self-mulching horizon, or thin, surface crusty horizon; and
  3. Slickensides and/or lenticular peds occur at some depth in the solum. See Comment below.


In some clay soils it may be difficult to decide if sufficient cracks are present, or at the time of inspection the soil may be too moist to exhibit cracking. Also, in arid zone clay soils which commonly have high salt contents, the soil structure may be so fine and strong granular, or 'puffy', that it is difficult to decide if cracks are present or not. In such soils it is also obviously difficult to discern slickensides or lenticular peds. In yet other clay soils (up to 50% clay or more) cracks may develop but slickensides and lenticular peds are apparently not present.

Because cracking, slickensides and lenticular peds are essentially used as evidence to indicate shrink-swell behaviour, it is desirable that surrogate measurements be available if the morphological evidence is lacking or cannot be determined. See Vertic properties.



Of the soils entered in the data base, the most common class was Black (40%) which is probably a reflection of the agricultural importance of these soils.

Great Groups

These may not all apply to each suborder, in particular our knowledge of the Aquic suborder is limited.


Apart from the Peaty forms, each of the above soil surface conditions tends to reform despite cultivation or surface trampling. There may be a problem in identifying the self-mulching condition in periods of initial drying, i.e. in assessing the stability of the surface flake which forms following rainfall. If there is doubt as to whether a soil is self-mulching or has only a pedal surface, it is suggested that the latter condition be recorded, i.e. use the self-mulching great group only for those soils where the condition is not in doubt. It may be difficult to determine the surface condition if a dense grass sward is present. In this situation it will be necessary to look for a patch of bare ground, or even to kill the grass with herbicide and return at a later date. Note also that large soil units bounded by cracks are not considered to be coarse peds. It is usually necessary to examine these soils in the moist state to determine their degree of pedality.

Fifty four percent of the soils classified were judged to be Self-mulching, with 35% classed as Epipedal.


It is thought that the following subgroups will be required for most of the suborders and great groups. Note that some of the differentiating criteria are not mutually exclusive, and thus sometimes it has been a subjective decision as to which attributes have priority in the key.


It should be noted that all the Endoacidic soils classified are also Endohypersodic, with some also being Epihypersodic. Additionally, some Epicalcareous-Epihypersodic soils are Endoacidic at depth. It is not possible to cater for all these combinations.

The most common subgroup recorded was Haplic, although this accounted for only 26% of the subgroups classified. It was dominantly associated (64%) with the Black Vertosols.

Family Criteria

Because of the uniform clayey nature of these soils and their usual lack of distinct horizonation, several of the usual family criteria are not appropriate for Vertosols. Field texture in these soils may not be a reliable guide to actual clay content (see McDonald et al. 1990 p.121), and it may also be difficult to achieve consistent results between operators. Hence it is thought more appropriate to provide for a subdivision of actual clay content as determined by laboratory analysis. The classes used are similar to those used for clayey particle-size classes in Soil Taxonomy. Other criteria used are gravel content of surface and A1 horizon and soil depth.

Gravel of 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%

Clay content of upper 0.1 m (excluding any surface crusty horizon)

Fine [Q] : < 45% clay
Medium fine [R] : 45 - 60% clay
Very fine [S] : > 60% clay

B horizon maximum clay content

Fine [Q] : < 45% clay
Medium fine [R] : 45 - 60% clay
Very fine [S] : > 60% 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 Note that there is no crack frequency criterion as in the Factual Key.

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