The Australian Soil Classification

Third Edition

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Arenosols [RE]

[Pronounced Ah-ren-oh-sols]

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Concept

The core concept of this Order is "deep sandy soils".

Arenosols accommodate soils with predominantly sandy field textures (≤10% clay content), and with no horizons containing more than 15% clay within the upper 1.0 m of the profile. The presence of argic horizons are the only exception. Arenosols generally have no observable peds apart from some structural development in the A1 horizon. The upper 1.0 m of the soil profile can only contain relatively small amounts of coarse fragments or coarse, hard segregations and does not contain any hard layers such as pans or rock. Arenosols occur extensively in inland arid areas, in and adjacent to waterways, near to the coast (especially in the west), but are also present in many other parts of Australia. This Order incorporates the most widespread and abundant soils in Australia.

Distribution of Arenosols in Australia.
Soil Profile (View type example photo of Yellow Arenosol).

Definition

Soils that have, within the upper 1.0 m of the soil profile:

1. A sandy field texture (i.e. a field texture of sand, loamy sand or clayey sand) in one or more layers or horizons with a combined thickness of at least 0.8 m; and
2. No layer or horizon with a clay content that exceeds 15% (i.e. heavy sandy loam [SL+] or heavier) excluding argic horizon/s; and
3. ≤10% (by visual abundance and weighted average) of coarse fragments and/or hard segregations >2 mm in size; and
4. No hard layers (cemented pans, other cemented materials, rock, saprock or saprolite that do not soften when moist¹)

¹this qualification has been added since publication and is not reflected in CSIRO March 2021 published edition. The purpose is to not exclude from Arenosols soils with layers in the top 1.0 m that are hard when dry but soften when moist.

Comment

As B horizons are difficult to identify consistently in some Arenosols, specific mention of a B2 horizon is omitted from some Suborders. Arenosols will obviously grade to Kandosols and some difficulty may be experienced in separating them. Here Kandosols must have a clearly distinguishable, well-developed B2 horizon with more than 15% clay whereas Arenosols have less than 15% clay.

Reclassification may also be required for other sandy soils where deep examination below 1.0 m reveals deep more clayey B horizons. See How to Classify for assistance with determining whether the layer is a B or D horizon. If the layer is a D horizon, the soil remains classified as an Arenosol.

Bleached or Grey Arenosols are distinguished from Podosols by the absence of Podosol diagnostic horizons. These horizons can occur below 1.0 m deep and commonly at considerable depth. If no deep examination has been done in similar soils in similar environments, then the soil should classify as a Bleached or Grey Arenosol with a confidence level of 4. If evidence at a later date reveals the presence of Podosols diagnostic horizons at depth, the soil will need to be reclassified.

Some Arenosols may include one or more thin argic horizons (also termed lamellae) which are usually 5-10 mm thick.

Arenosols will also grade to Tenosols. This third edition of the Australian Soil Classification reflects a major change to the Tenosol Order. Many sandy soils previously classified as the colour-linked Orthic Suborders of Tenosols will now classify as Arenosols.

As the Arenosols Order includes soils with negligible development many deep sandy soils previously described as Rudosols will now classify as Arenosols.

This third edition of the Australian Soil Classification also reflects a significant change to the Calcarosol Order. Many deep sandy soils with pedogenic carbonates previously classified as Shelly, Calcic or Hypocalcic Calcarosols will now classify as Carbonatic or Calsilic Arenosols.

Suborders

• Soils that are not highly saline (EC <2 dSm^-1; 1:5 H₂O) and dominantly consist of sand-sized gypsum crystals. These crystals may not feel like sands when hand texturing due to their partial dissolution in water.
Hypergypsic [FJ]
• Soils that are highly saline (EC >2 dSm^-1; 1:5 H₂O), often salt-encrusted, frequently stratified, but do not have a permanent or seasonal water table and do not show any evidence of episodic wetting by groundwater, such as mottling.
Hypersalic [CS]
• Soils with a peaty, humose, melacic or melanic horizon. A conspicuously bleached A2 horizon is not present.
Chernic [BE]
• Soils which are calcareous throughout (at least the upper 1.0 m of the soil profile). The upper 0.1 m of the soil profile consists of dominantly fine earth carbonate (visual estimate) and/or contains more than 40% (by analysis) of fine earth carbonate.
Carbonatic [JT]
• Other soils which are calcareous throughout (at least the upper 1.0 m of the soil profile), or calcareous at least below the A1 or Ap horizon, or calcareous within a depth of 0.2 m (whichever is shallower). Calsilic [JN]
• Soils that consist dominantly of unconsolidated mineral materials which are distinct, not or only slightly gravelly (<10% >2 mm) sedimentary layers or buried soils but salinity is not high (EC<2 dSm-1; 1:5 H₂O).
Stratic [ER]
• Soils with a conspicuously bleached A2 horizon.
Bleached [GZ]

Soils in which the dominant colour class in the major part of the upper 1.0 m of the soil profile is:

• Red.
Red [AA]
• Brown.
Brown [AB]
• Yellow.
Yellow [AC]
• Grey.
Grey [AD]
• Black.
Black [AE]

Comment

The Hypergypsic soils normally occur as gypsum lunettes and the Hypersalic soils are most common in many of the saline playas of the arid interior of the continent. The Chernic soils typically occur in low lying, wetter, cooler areas of southern Australia where organic matter accumulates in surface horizons. The Carbonatic and Calsilic soils occur on coastal dunes as well as inland spreads of calcareous sands in southern Australia. The Bleached, Red, Brown, Yellow, Grey and Black soils mainly cater for the widespread siliceous dunes and sandsheets, as well as some coastal dunes, with the soils largely concentrated in southern Australia. The Stratic soils occur where sands have been deposited through water action.

The Carbonatic soils are typically highly calcareous and dominated by sand-sized fine-earth carbonates throughout the profile. The Carbonatic Suborder in Arenosols partially replaces the former Shelly Suborder in Calcarosols. Other shelly soils are is now restricted to soils dominated by shell fragments in Rudosols.

The Calsilic Suborder includes sands that are calcareous throughout (with the possible exception of the surface) but are generally lower in carbonates and more siliceous than the Carbonatic Suborder.

The most commonly recorded Suborders are Carbonatic, Calsilic, Bleached, Red, Brown, Yellow, and Grey.

Great Groups

No Great Groups are presently proposed for the Hypergypsic and Stratic Suborders as data are limited, plus the limited pedological development of these soils means that subsoils are generally only weakly developed.

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.

Hypersalic Arenosols

• Soils in which sulfuric material (at least 0.15 m thick) occurs within the upper 1.5 m of the soil profile.
Sulfuric [EV]

Note that the Sulfuric Great Group can be replaced by the following Great Group where appropriate evidence is available.

• Soils in which both monosulfidic materials and sulfuric material (at least 0.15 m thick) occur within the upper 1.5 m of the soil profile.
Monosulfidic-Sulfuric [IW]
• Soils in which sulfidic materials occur within the upper 1.5 m of the soil profile.
Sulfidic [EU]

Note that the Sulfidic Great Group can be replaced by the following Great Groups where appropriate evidence is available.

• Soils in which both monosulfidic material and hypersulfidic material occur within the upper 1.5 m of the soil profile.
Monohypersulfidic [IX]
• Other soils in which hypersulfidic material occurs within the upper 1.5 m of the soil profile.
Hypersulfidic [IZ]
• Soils in which both monosulfidic material and hyposulfidic material occur within the upper 1.5 m of the soil profile.
Monohyposulfidic [JA]
• Other soils with hyposulfidic material within the upper 1.5 m of the soil profile.
Hyposulfidic [JC]
• Soils with a gypsic horizon within the upper 1.0 m of the soil profile.
Gypsic [BZ]
• The major part of the upper 0.5 m of the soil profile consists of materials dominated (>50%) by halite crystals.
Halic [CC]
• The major part of the upper 0.5 m of the soil profile consists of materials with < 50% halite crystals.
Subhalic [JK]

Chernic Arenosols

Suitable Great Groups may be found as listed for Bleached and coloured Arenosols

Carbonatic and Calsilic Arenosols

The Great Groups that include hard layers (cemented pans, other cemented materials, rock, saprock or saprolite) can only apply to layers that occur below 1.0 m.

• Soils with an argic horizon within the B horizon.
Argic [AP]
• Soils with a gypsic horizon.
Gypsic [BZ]
• Soils that are not calcareous in the A1 or Ap horizon, or to a depth of 0.2 m if the A1 horizon is only weakly developed.
Epibasic [IB]
• Soils in which the upper 0.1 m of the soil profile 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% ¹ (by analysis) of fine-earth carbonate. Hypervescent [CP]
• Soils that directly overlie marl.
Marly [DD]
• Soils that directly overlie a red-brown hardpan.
Duric [BJ]
• Soils that directly overlie a calcrete pan.
Petrocalcic [DZ]
• Soils that directly overlie hard rock.
Lithic [CZ]
• Soils which directly overlie partially weathered or decomposed rock or saprolite.
Paralithic [DU]
• Other soils that directly overlie unconsolidated mineral materials.
Regolithic [GF]

Comment

Epibasic and Hypervescent Great Groups are only applicable to Calsilic Suborder.

Chernic, Bleached, Red, Brown, Yellow, Grey and Black Arenosols

The Great Groups that include hard layers (cemented pans, other cemented materials, rock, saprock or saprolite) can only apply to layers that occur below 1.0 m. In Great Groups that include a ferric horizon overlying a hard layer (i.e. Ferric-Duric, Ferric-Petroferric and Ferric-Reticulate) the ferric horizon may begin within the top 1.0 m.

• Soils which have a ferric horizon and overlie a red-brown hardpan.
Ferric-Duric [FK]
• Other soils which overlie a red-brown hardpan.
Duric [BJ]
• Soils which contain a ferric horizon and which overlie ferricrete, a petroferric horizon or a petroreticulate horizon.
Ferric-Petroferric [GE]
• Soils which contain a ferric horizon and which overlie a reticulate horizon.
Ferric-Reticulate [IS]
• Other soils which overlie ferricrete, a petroferric horizon or a petroreticulate horizon.
Petroferric [EA]
• Soils which overlie a reticulate horizon.
Reticulate [EF]
• Soils which overlie a siliceous pan.
Silpanic [EM]
• Other soils with a ferric horizon.
Ferric [BU]
• Soils with a bauxitic horizon.
Bauxitic [AS]
• Soils with a manganic horizon.
Manganic [DC]
• Soils which have andic properties and have formed in basaltic tephric materials that may be visibly stratified.
Andic [AK]
• Soils which have formed in tephric materials that may be visibly stratified.
Tephric [HF]
• Soils with an argic horizon.
Argic [AP]
• Soils in which the major part of the upper 1.0 m has a distinct gritty feel.
Gritty [JQ]
• Soils with a gypsic horizon in the upper 1.0 m of the soil profile.
Gypsic [BZ]
• Soils in which the major part of the upper 1.5 m of the soil profile consists of visible heavy or opaque minerals (>3%) that may also be visibly stratified (identifiable by wet panning in the field).
Gravic [JR]
• Soils in which the fine earth carbonate is evident only as a slight to moderate effervescence (1 M HCl), and/or contain less than 2% fine earth 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 fine earth 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 containing fine earth carbonate.
Calcic [BD]
• Soils which overlie a hard calcrete pan.
Petrocalcic [DZ]
• Soils with a transitional horizon (C/B) occurring in fissures in the parent rock or saprolite which contains between 10 and 50% of B horizon material (including pedogenic carbonate).
Inceptic [IA]
• Soils which overlie hard rock.
Lithic [CZ]
• Soils which overlie partially weathered or decomposed rock or saprolite.
Paralithic [DU]
• Soils which overlie marl.
Marly [DD]
• Soils with a layer or horizon, other than the surface horizon, that has a light sandy loam texture (about 10-15% clay) that begins within the upper 1.0 m of the soil profile. Kandic Arenosols have affinities with Kandosols but are too sandy.
Kandic [JP]
• Soils with a layer or horizon, other than the surface horizon, that has a clayey sand or loamy sand texture (about 5-10% clay) that begins within the upper 1.0 m of the soil profile.
Tenic [JL]
• Other soils that, other than the surface horizon, have a sand texture (<5% clay) throughout at least the upper 1.0 m of the soil profile.
Palic [FH]

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.

Subgroups

No Subgroups are proposed for the Hypergypsic, Hypersalic, Carbonatic, Calsilic and Stratic Suborders. The Humose-Calcareous, Melanic-Calcareous and Calcareous Subgroups are not required for the Hypocalcic, Lithocalcic, Supracalcic, Hypercalcic, Calcic and Pertrocalcic Great Groups

Subgroups of Chernic, Bleached, Red, Brown, Yellow, Grey and Black Arenosols

• Soils with a peaty horizon.
Peaty [DW]
• Soils with a humose horizon and the major part of the upper 1.0 m of the soil profile is strongly acid.
Humose-Acidic [GY]
• Soils with a humose horizon and at least some part of the upper 1.0 m of the soil profile is calcareous.
Humose-Calcareous [GU]
• Other soils with a humose horizon.
Humose [CK]
• Soils with a melacic horizon and the major part of the upper 1.0 m of the soil profile is not strongly acid.
Melacic-Basic [FU]
• Other soils with a melacic horizon.
Melacic [DG]
• Soils with a melanic horizon and the major part of the upper 1.0 m of the soil profile is strongly acid.
Melanic-Acidic [FV]
• Soils with a melanic horizon and at least some part of the upper 1.0 m of the soil profile is calcareous.
Melanic-Calcareous ³[FC]
• Other soils with a melanic horizon.
Melanic [DK]
• Soils with all the requirements for a peaty horizon except the thickness.
Subpeaty [ID]
• Soils in which the major part of the upper 1.0 m of the soil profile is strongly acid.
Acidic [AI]
• Soils in which at least some part of the upper 1 m of the soil profile is calcareous.
Calcareous⁴ [BC]
• Other soils which are not strongly acid or calcareous.
Basic [AR]

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.

Gravel of surface and/or A1 horizon

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

Soil surface texture

Peaty	[J]	: Dominated by organic materials
Sandy	[K]	: S-LS-CS (≤10% clay)
Loamy	[L]	: SL-L (10-20% clay)

Maximum texture below the surface or A1 (within the upper 1.0 m of the soil soil profile)

Sandy	[K]	: S-LS-CS (≤10% clay)
Loamy	[L]	: SL-L (10-20% clay)

Soil depth

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

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¹Based on numerous fine-earth analyses by Primary Industries, South Australia.

²Note that the Humose-Calcareous Subgroup is not required for the six calcic Great Groups.

³Note that the Melanic-Calcareous Subgroup is not required for the six calcic Great Groups.

⁴Note that the Calcareous Subgroup is not required for the six calcic Great Groups.

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