Chapter 11: Regosolic Order
A diagrammatic representation of profiles of some subgroups of the Regosolic order is shown in Figure 38. Individual subgroups may include soils that have horizon sequences different from those shown. In the description of each subgroup, presented later in this chapter, a common horizon sequence is given; diagnostic horizons are underlined and some other commonly occurring horizons are listed.
Regosolic soils do not contain a recognizable B horizon at least 5 cm thick and are therefore referred to as weakly developed. The lack of a developed pedogenic B horizon may result from any of a number of factors: youthfulness of the material, recent alluvium; instability of the material, colluvium on slopes subject to mass wasting; nature of the material, nearly pure quartz sand; climate, dry cold conditions. Regosolic soils are generally rapidly to imperfectly drained. They occur under a wide range of vegetation and climates.
Pedogenic development in Regosolic soils is too weak to form a recognizable B horizon that meets the requirements of any other order. They have none of the following: solonetzic B, Bt, podzolic B, Bm at least 5 cm thick, vertic horizon, evidence of gleying strong enough to meet the requirements of Gleysolic soils, organic surface horizons thick enough to meet the requirements of Organic soils, or permafrost within 1 or 2 m if the soils are strongly cryoturbated. They may have L, F, and H or O horizons. Also they may have an Ah or Ap horizon less than 10 cm thick or of any thickness if there is no underlying B horizon at least 5 cm thick and characteristics of the Ah or Ap do not satisfy the criteria of a chernozemic A horizon.
Distinguishing Regosolic Soils from Soils of Other Orders
Guidelines for distinguishing Regosolic soils from soils of other orders with which they might be confused follow:
Chernozemic Some Humic Regosols might be confused with Rego subgroups of Chernozemic soils. Such soils (usually Ah or Ap, C profiles) are classified as Humic Regosols if the Ah or Ap horizon fails to satisfy the requirements of a chernozemic A because of any of the following:
- It is a moder rather than a mull A horizon.
- It lacks structure.
- The soil climate is outside the range specified for a chernozemic A.
- It has a low base saturation.
Vertisolic Vertisolic soils must have both a slickenside and a vertic horizon within the control section. Regosolic soils do not have a vertic horizon.
Brunisolic Brunisolic soils must have a B horizon (Bm, Btj, Bfj) at least 5 cm thick. Regosolic soils usually do not have a B horizon and in those that do it is less than 5 cm thick.
Gleysolic Some Gleysolic soils resemble Regosolic soils by having very weakly developed horizons. However, Gleysolic soils must have dull colors or mottles that indicate strong gleying; Regosolic soils do not.
Cryosolic Cryosolic soils have permafrost within 1 m of the surface or 2 m if strongly cryoturbated; Regosolic soils do not.
The Regosolic order is divided into two great groups based on the presence or absence of a significantly developed Ah or dark colored Ap horizon as shown in the Regosolic order chart.
Subgroups are based upon evidence of either relative stability of the material or periodic deposition of material and of gleying. Regosols with saline, cryic, and lithic features are differentiated taxonomically either at the family (lithic, some cryic) or the series (saline) levels. These features may also be indicated as phases of a subgroup, great group, or order.
|Diagnostic horizons are underlined|
|Ah or dark colored Ap||<10 cm||≥10 cm thick|
|Bm||absent or <5 cm||absent or <5 cm|
|Regosol||Orthic Regosol O.R|
|Cumulic Regosol CU.R|
|Gleyed Regosol GL.R|
|Gleyed Cumulic Regosol GLCU.R|
|Humic Regosol||Orthic Humic Regosol O.HR|
|Cumulic Humic Regosol CU.HR|
|Gleyed Humic Regosol GL.HR|
|Gleyed Cumulic Humic Regosol GLCU.HR|