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Vertosols
Main Characteristics
- Uniform texture profile, which is clayey (fine-textured) throughout.
- The soils swell on wetting and shrink greatly on drying, forming deep cracks. These cracks are not always apparent at the surface.
- Gilgais are common, although they are only weakly developed (or absent) on the brown and red clays.
- The soil profile is usually deep to very deep (>150 cm). It is strongly structured with dominantly smooth-faced blocky peds throughout.
- The soil material at the surface is sticky when wet and self-mulching when dry, forming a loose layer about 2-10 cm thick of granular or very fine blocky aggregates.
- On average, the surface soil is 10 cm thick (common range is 5-15 cm) light to medium clay, gradually changing into heavy clay at depth.
- Usually the soil profile is calcareous throughout, often containing high amounts of carbonate at shallower depths. The soil reaction is moderately alkaline in the surface horizons and increases to strongly alkaline in the subsoils.
- Accumulations of salts and gypsum are common in the deep subsoils.
- Soil profiles included in Group 3 (see below), have bleached A2 horizons (subsurface soil layers). These horizons do not occur in the soils of Groups 1 and 2 (see below).
Description of Soil Groups
There are three main soil groups within Vertosols:
Group 1. Black and Grey Self-Mulching Vertosols
Group 2. Brown and Red Self-Mulching Vertosols
Group 3. Vertosols with Bleached Subsurface Horizons
Group 1. Black and Grey Self-Mulching Vertosols.
These soils are commonly known as the "Wimmera Self-mulching or Friable, Grey Clays". They are widespread in the survey area, usually occurring on the lower slopes and the level parts of the undulating plains. The soil profiles are deep to very deep (>150 cm) and are clayey throughout (uniform fine-textured).
Surface Soil
About 10 cm thick (common range is 5-15 cm). Grey to grey-brown light to medium clay, strong granular soil aggregates which are self-mulching. Soil consistence is soft to slightly hard (dry), friable to very friable (moist), plastic and sticky (wet). Gradual to clear boundary to:
Subsoil
Very dark grey to grey-brown medium to heavy clay, strong fine to medium blocky structure, smooth-faced peds. The soil aggregates are moderately hard to very hard (dry), friable to moderately friable (moist), plastic and sticky (wet).
Commonly, the subsoil changes gradually into paler or darker brown colors and strong coarse blocky structure with depth. However, some subsoil colors may remain unchanged to depths greater than 150 cm.
Streaks of surface soil material are often found as ‘in-fills’, to various depths in the subsoil.
Soil Inclusions
Trace to slight amounts of hard carbonate (lime) nodules (2-10 mm in size) are usually found scattered on the surface. Varying amounts of soft and/or hard lime occur throughout the soil profile.
Typically, moderate to high concentrations of soluble salts are commonly found in the subsoils below 30-50 cm and varying amounts of gypsum often occur as fine crystals in the deep subsoils.
Soil Reaction (pH)
The soil reaction trend shows an increase in pH value down the profile. The soils are neutral to alkaline at the surface, becoming strongly alkaline with depth.
Seasonal Cracking
Seasonal cracking is a prominent characteristic of these clays as they expand and contract significantly with moisture changes. Upon drying, they develop cracks with a minimum occurrence of one crack at least 6 mm wide and 30 cm deep, per square meter. Such cracks, however, may not be apparent at the soil surface.
Gilgais
Gilgais (melon-holes, crab-holes etc.) are a common feature of these soils. The gilgai depressions (troughs) range from 3 to 20 m in diameter, separated by a network of mounds (puffs) 1 to 3 m across. On continuously cropped land, gilgais become obliterated at the surface due to grading, cultivation and seedbed preparation. However, they reappear when the land is left undisturbed for a number of wetting and drying seasons. The puffs are usually raised up to 30 cm above ground level and the depressions vary in depth from 5 to 50 cm.
In the present survey, the Black and Grey Self-mulching Vertosols (referred to as Kalkee Group) include the following soil series:
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Group 2. Brown and Red Self-Mulching Vertosols.
These are the brown and red counterparts of the Black and Grey Self-mulching Vertosols (Group 1), with which they are intermingled in many areas of the survey. Typically, the brown and red clays occur on the upper slopes and crests of the undulating plains. Also they often intermix, as mosaics, with the grey clays on the intermediate slopes and the level areas.
Many of the soil profile characteristics are similar to those of the dark grey and grey self-mulching cracking clays. The soil profiles are deep to very deep (>150 cm) and are clayey throughout (uniform fine-textured).
Surface Soil
Upon wetting and drying, a thin layer (2-5 mm) of a fragile crust (somewhat sandy) is often formed on the undisturbed surface soil.
On average, the surface soil is about 10 cm thick (common range is 5-15 cm), grey brown to reddish brown medium clay (occasionally sandy clay). The soil material is moderately to strongly pedal consisting of granular and/or blocky aggregates which are self-mulching. Commonly, these aggregates are slightly soft to very hard (dry), moderately friable to non-friable (moist), plastic and very sticky (wet). Clear to sharp boundary to:
Subsoil
Brown to red-brown or red heavy clay, strong fine to coarse blocky structure, smooth-faced peds. The soil aggregates are usually hard to very hard (dry), slightly friable to non-friable (moist), plastic and very sticky (wet).
Subsoil colours may remain, more or less, unchanged to greater depths (>150 cm) or gradually become paler or yellower in the deep subsoils.
Streaks of surface soil material are often found as ‘in-fills’, to various depths in the subsoil.
Soil Inclusions
Trace to slight amounts of hard carbonate (lime) nodules (2-10 mm in size) are usually found scattered on the surface. Varying amounts of soft and hard lime occur throughout the soil profile.
Commonly, the soluble salts are in moderate concentrations in the surface soils and markedly increase with depth. Varying amounts of gypsum often occur as fine crystals in the deep subsoils.
Soil Reaction (pH)
The soil reaction trend shows an increase in pH value down the profile. Typically, the soils are moderately alkaline at the surface becoming strongly alkaline with depth.
Seasonal Cracking
These clays swell on wetting and shrink greatly on drying, forming deep cracks. However, these cracks may not be apparent at the soil surface.
Gilgais
In general, gilgais (melon-holes, crab-holes etc.) are not as common on these soils as on the dark grey and grey self-mulching cracking clays. On the red clays, gilgais are usually absent and on the brown clays they are only weakly developed. However, in many parts of the gilgai plains, the brown and grey clays often intermix with each other, occupying the gilgai puffs and depressions respectively.
In the present survey, the brown and red self-mulching cracking clays (referred to as Murra Warra Group) have been subdivided into two sub-groups, each of which include two soil series. These sub-groups and their corresponding series are as follows:
Brown Self-mulching Vertosols
Red Self-mulching Vertosols
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Group 3. Vertosols with Bleached Subsurface Horizons.
These soils occupy localised areas in the undulating plains and their overall distribution in the survey is quite limited. They occur on the flood plains, low lying areas and some gilgai depressions in the gently undulating plains.
Soil profiles of this group have similar characteristics to their counterparts included in the two groups discussed above, except for the following differences:
- The soil profile has a bleached A2 horizon below the immediate surface. The A2 horizon varies in its degree of development from as much as a thick conspicuously bleached layer (up to 15 cm) to as little as only a few nests of pale (near white) soil material scattered at the interface between the A and B horizons.
- Soil profiles with bleached A2 horizons are often less calcareous (particularly in the upper soil layers), less friable and contain slightly more sand in their surfaces (ie. sandy clay A1 and/or A2) than the non-bleached profiles.
In the present survey, this group includes the following series:
