Calcarosols [CA]
[Pronounced Cal-care-oh-sols]
Concept
The soils in this Order are usually calcareous throughout the profile, often highly so. They constitute a widespread and important group of soils in southern Australia.
Distribution of Calcarosols in Australia.
Soil Profile (View type example photo of Supracalcic Calcarosol).
Definition
Soils that:
- Are either calcareous throughout the solum - or calcareous at least directly below the A1 or Ap horizon, or within a depth of 0.2 m (whichever is shallower). Carbonate accumulations must be judged to be pedogenic1, ie. are a result of soil forming processes in situ (either current or relict). Soils dominated by non-pedogenic calcareous materials such as fragments of limestone or shells are excluded. See also calcrete, and
- Do not have deep sandy profiles that have a field texture of sand, loamy sand or clayey sand in 80% or more of the upper 1.0 m.
Comment
A difficulty may arise in separating those Calcarosols that are not calcareous throughout from calcareous Kandosols and from Tenosols containing pedogenic carbonate. However, in the latter two soils it is usual for the carbonate to occur in the lower part of the B horizon, and not immediately below the A horizon. Even so, transitional cases will arise where it becomes a matter of judgement as to which order the particular soil is best placed. Similar transitions might occur between shallow Calcarosols and Arenic Rudosols overlying a layer of calcrete or limestone. Again, Calcareous Arenic Rudosols will occur where recent aeolian calcareous material has been deposited.
In landscapes dominated by wind-blown calcareous material it may be difficult to determine if the carbonates are of pedogenic origin. Deep calcareous sands, which commonly occur in this situation, are now included in the Arenosols order.
Soils with minimal soil development and dominated by coarse fragments of shells or other aquatic animals are included in Shelly Rudosols.
In dune landscapes, where these soils frequently occur, it is common to find evidence of post-European settlement deflation and layering of soil profiles caused by wind erosion and consequent deposition. Unless the surface depositional material is 0.3 m or more thick, it is ignored in the classification and treated as a phase. (see 'What do we classify?').
Suborders
- Soils that dominantly consist of gypsum crystals which are sand-sized or finer. Hypergypsic [FJ]
- Soils which are calcareous throughout. The upper 0.1 m of the solum consists of dominantly fine earth carbonate (visual estimate) and/or contains more than 40% (by analysis) of fine earth carbonate. Carbonatic [JT]
- Soils in which the carbonate is evident only as a slight to moderate effervescence (1M 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 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.
The Carbonatic Suborder partially replaces the former Shelly Suborder which is now restricted to soils dominated by shell fragments in Rudosols. The Carbonatic soils are typically highly calcareous and dominated by fine-earth carbonates throughout the profile.
Of the profiles classified, the Calcic and Hypercalcic suborders are the most common.
Great Groups
If a diagnostic feature in the key begins more than 1.5 m from the soil surface it may not have a significant impact on the performance of the soil. Refer to diagnostic features in the glossary for guidance on the use of such features in the classification.
Hypergypsic Calcarosols
Insufficient information is available to subdivide these soils further.
Other Calcarosols
Not all Great Groups will be relevant for every suborder, for example, Rendic will be required only for the Hypercalcic suborder.
- Soils that directly overlie a red-brown hardpan. Duric [BJ]
- Soils that directly overlie a calcrete pan. Petrocalcic [DZ]
- Soils in which the A horizon directly overlies a Bk horizon consisting almost entirely of soft carbonate (>80%). Rendic [EE]
- Soils with an argic horizon within the B horizon. Argic [AP]
- Soils in which the major part of the B horizon has a grade of structure that is stronger than weak. Pedal [DY]
- Soils that directly overlie hard rock. Lithic [CZ]
- Soils which directly overlie partially weathered or decomposed rock or saprolite. Paralithic [DU]
- Soils that directly overlie marl. Marly [DD]
- Other soils that directly overlie unconsolidated mineral materials. Regolithic [GF]
Subgroups
The following subgroups will not necessarily be applicable to all great groups of each suborder, and not all subgroups are mutually exclusive. The Supravescent and Hypervescent classes are not required for the Carbonatic suborder. The Supravescent and Hypervescent classes may also be Epihypersodic or Endohypersodic. However, the high content or absence of carbonate in the upper 0.1m is thought to have more influence on land use than high sodicity. A number of soils has been recorded as having a conspicuously bleached A2 horizon. In many cases, however, this may be a reflection of high contents of soft carbonate, hence this feature has not been used as a class differentia.
If a diagnostic feature in the key begins more than 1.5 m from the soil surface it may not have a significant impact on the performance of the soil. Refer to diagnostic features in the glossary for guidance on the use of such features in the classification.
- Soils with a melanic horizon overlying a B horizon in which at least 0.3m has vertic properties. Melanic-Vertic [DN]
- Other soils with a melanic horizon. Melanic [DK]
- Other soils with a B horizon in which at least 0.3 m has vertic properties. Vertic [EX]
- Soils in which the B horizon is strongly subplastic and the B or BC horizon contains a gypsic horizon. Gypsic-Subplastic [FL]
- Other soils with a strongly subplastic B horizon. Subplastic [ET]
- Soils with a gypsic horizon within the B or BC horizon. Gypsic [BZ]
- Soils that are not calcareous in the A1 or Ap horizon, or to a depth of 0.2m if the A1 horizon is only weakly developed. Epibasic [IB]
- Soils in which the upper 0.1 m of the solum consists of dominantly soft, finely divided carbonate (visual estimate), and/or contains more than 40%2 (by analysis) of soft, finely divided carbonate. Supravescent [HK]
- Soils in which the upper 0.1 m of the solum consists of more than 20% fine earth carbonate (visual estimate using a 10 x hand lens), and/or has a strong effervescence with 1 M HC1, and/or contains more than 8%2 (by analysis) of fine earth carbonate. Hypervescent [CP]
- Soils in which at least some subhorizon within the upper 0.5 m of the solum has an ESP of 15 or greater. Epihypersodic [BR]
- Soils in which an ESP of 15 or greater occurs in some subhorizon below 0.5 m. Endohypersodic [BP]
- Other soils. Ceteric [IC]
Family Criteria
Use of the term A horizon may be inappropriate for some of these soils because of either minimal development due to an arid environment, or common surface deflation or accumulation caused by wind. Hence it is thought better to use the term surface soil for texture and to delete the thickness criteria. In general, surface soil in this context will probably be in the range of 0.1-0.2 m in thickness. For the Calcarosols, a criterion is used to indicate the thickness above the upper boundary of the Bk horizon.
Thickness of soil above upper boundary of Bk horizon (if present)
| Thin | [A] | : <0.1 m |
|---|---|---|
| Moderately thick | [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% |
Surface soil texture
| Peaty | [J] | : Dominated by organic materials |
|---|---|---|
| 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 (more than 35% clay) |
B horizon maximum texture3
| 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 (more than 35% clay) |
Soil depth
| Very shallow | [T] | : <0.25 m |
|---|---|---|
| Shallow | [U] | : 0.25 - <0.5 m |
| Moderately deep | [V] | : 0.5 - <1.0 m |
| Deep | [W] | : 1.0 - <1.5 m |
| Very deep | [X] | : 1.5 - 5 m |
| Giant | [Y] | : >5 m |
Water repellence of surface soil
| Non water repellent | [NR] | : Water absorbed in 10 seconds or less |
|---|---|---|
| Water repellent | [WR] | : Water takes more than 10 seconds and 2 Molar ethanol takes 10 seconds or less to be absorbed into soil |
| Strongly water repellent | [SR] | : 2 Molar ethanol takes more than 10 seconds to be absorbed into soil |
1 The carbonate is a result of soil-forming processes, in contrast to fragments of calcareous rock such as limestone. See also calcrete.
2 Based on numerous fine earth analyses by Primary Industries, South Australia.
3 This refers to the most clayey field texture category.