Organosols [OR]
[Pronounced Or-gan-oh-sols]
Concept
This class caters for most soils dominated by organic materials Although they are found from the wet tropics to the alpine regions, areas are mostly small except in south west Tasmania. There have been few previous attempts to subdivide these soils and substantial data are limited to Tasmania.
Distribution of Organosols in Australia.
Soil Profile (View type example photo
of Hemic Organosol).
Definition
Soils that are not regularly inundated by saline tidal waters and either:
- Have more than 0.4 m of organic materials within the upper 0.8 m. The required thickness may either extend down from the surface or be taken cumulatively within the upper 0.8 m; or
- Have organic materials extending from the surface to a minimum depth of 0.1 m; these either overlie a mineral soil horizon or unconsolidated mineral materials no thicker than the organic materials above, or directly overlie rock or other hard layers, partially weathered or decomposed rock or saprolite, or overlie fragmental material such as gravel, cobbles or stones in which the interstices are filled or partially filled with organic material. In some soils there may be layers of humose, melacic and/or melanic horizon material underlying the organic materials and overlying the substrate.
Comment
Soils with peaty horizons that do not meet the organic materials requirements of Organosols are catered for in other Orders, commonly Hydrosols. Organosols may classify as a buried soil if overlain by aeolian or fluvial deposits that may have undergone other developmental processes. If the overlying material is less than 0.3 m and can only qualify as a Rudosol, it is regarded as a depositional phase of the Organosol below.
Suborders
- Soils in which the dominant organic material, by thickness, is fibric peat. Fibric [BW]
- Soils in which the dominant organic material, by thickness, is hemic peat. Hemic [CE]
- Soils in which the dominant organic material, by thickness, is sapric peat. Sapric [EH]
Comment
The terms fibric, hemic and sapric are essentially the same as defined in the World Reference Base (2015) and Soil Taxonomy (Soil Survey Staff 2014) and give an indication of the relative decomposition of the organic materials If the proportions of peats in a profile are such that no peat type is dominant then the peat type with the most advanced level of decomposition should be selected.
In some north Queensland seasonal swamps, thick peats can have 0.3–0.4 m of sapric over hemic and/or fibric peat. Conversely many organic moorland soils found in the remote south western wilderness area of Tasmania often grade from fibric and hemic peat through to an underlying sapric peat. When more data are available it may be necessary to modify the Suborder definitions to cater for soils where the type of peat changes with depth.
Great Groups
It is likely that not all of the great groups below will be applicable to each suborder. It is also likely that other great groups will be required as knowledge increases.
- Soils that are more or less freely drained and are never saturated for more than several days unless rain is falling and contain organic materials which occur as in Definition (ii) of Organosols. Folic [IF]
- Soils in which sulfuric material (at least 15 cm thick) occurs within the upper 1.5 m of the profile. Sulfuric [EV]
- Soils in which both monosulfidic material and sulfuric material (at least 15 cm thick) occur within the upper 1.5 m of the profile. Monosulfidic - Sulfuric [IW]
- Soils in which sulfidic materials occur within the upper 1.5 m of the profile. Sulfidic [EU]
- Soils in which both monosulfidic material and hypersulfidic material occur within the upper 1.5 m of the profile. Monohypersulfidic [IX]
- Other soils in which hypersulfidic material occurs within the upper 1.5 m of the profile. Hypersulfidic [IZ]
- Soils in which both monosulfidic material and hyposulfidic material occur within the upper 1.5 m of the profile. Monohyposulfidic [JA]
- Other soils with hyposulfidic material within the upper 1.5 m of the profile. Hyposulfidic [JC]
- Soils in which the major part of the organic materials is calcareous. Calcareous [BC]
- Soils in which the major part of the organic materials is not calcareous but is not strongly acid. Basic [AR]
- Soils in which the major part of the organic materials is strongly acid. Acidic [AI]
Note: The sulfuric Great Group can be replaced by the following Great Group where appropriate evidence is available:
Note: The sulfidic Great Group can be replaced by the following Great Groups where appropriate evidence is available:
Subgroups
The following subgroups may not be relevant to all great groups of each suborder, and future investigations may reveal additional subgroups.
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 in which the organic materials directly overlie hard rock. Lithic [CZ]
- Soils in which the organic materials directly overlie partially weathered or decomposed rock or saprolite. Paralithic [DU]
- Soils with a marl layer either within or immediately below the section containing the organic materials. Marly [DD]
- Soils in which the organic materials directly overlie fragmental material such as Gravel, cobbles or stones in which the interstices are filled or partially filled with organic material. Rudaceous [HD]
- Soils in which layers of humose, melacic and/or melanic horizon material underlie the organic materials and overlie the substrate. Modic [IJ]
- Soils with a thin ironpan below the organic materials. Placic [EC]
- Soils with a layer (or layers) of unconsolidated mineral material within or below the organic materials but within 0.8 m of the surface. Terric [FS]
- Other soils with a layer (or layers) of unconsolidated mineral material which occurs below 0.8 m of the surface. Regolithic [GF]
Family Criteria
Texture classes specific to organic materials (and consistent with horizon definitions in the Field Handbook) describe the dominant texture of the uppermost organic materials, horizons or layers. These classes provide a useful insight to the formation processes of and inherent vulnerabilities to the uppermost organic materials.
Granular is applied if there is a layer at least 0.2 m thick that has a distinct granular or subangular blocky type of pedality (see Field Handbook). This condition occurs in some peat soils that have either naturally dried out, or have been drained or drained and cultivated, and are also known as earthy or ripened peats. In Australia it is known to occur with sapric peats, but it is uncertain if it occurs with hemic or fibric peats.
Ashy and Vitric reflect the influence of fire.
Nature of altered organic materials
(use only if feature present; choose dominant feature if more than one present)
| Granular | [P] | : Granular or subangular blocky type of pedality |
|---|---|---|
| Ashy | [HZ] | :ash material |
| Vitric | [JZ] | : ≥20% fusic material |
Cumulative thickness of uppermost organic materials
(sum of the consecutive O1, O2, P1 and P2 horizons)
| Moderately thick | [B] | : 0.1–<0.6 m |
|---|---|---|
| Thick | [C] | : 0.3–0.6 m |
| Very thick | [D] | : >0.6 m |
Gravel of the surface horizon
| Non-gravelly | [E] | : <2% |
|---|---|---|
| Slightly gravelly | [F] | : 2–<10% |
| Gravelly | [G] | : 10–<20% |
| Moderately gravelly | [H] | : 20–50% |
| Very gravelly | [I] | : >50% |
Dominant type or texture of the uppermost organic materials (O2, P1 or P2 if present)
| Surface organic material absent | [Z] |
|---|---|
| Fibric peat | [OA] |
| Hemic peat | [OB] |
| Sapric peat | [OC] |
| Sandy peat | [OD] |
| Loamy peat | [OE] |
| Clayey peat | [OF] |
Dominant texture of the B, C or D horizons directly underlying the deepest organic materials
| Texture material absent | [Z] | |
|---|---|---|
| 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 (> 35% clay) |
Soil depth
(measured from the soil surface including organic horizons)
| 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 |