Dark Gray Chernozem (DGC)
These soils have Chernozemic A horizons with characteristics indicative of eluviation associated with soils developed under forest vegetation. Dark Gray Chernozems usually occur under mixed native vegetation of trees, shrubs, forbs, and grasses in forest-grassland transition zones in areas of cold, subhumid soil climate. Virgin Dark Gray Chernozems usually have leaf mats (L-H horizons) overlying Ah or Ahe horizons. The peds of the A horizons may have dark-colored surfaces, but the crushed peds usually have gray or brownish colors of higher value or chroma. A "salt and pepper" effect, light gray spots, or bands on a darker matrix may be observable in the A horizons, which tend to have platy structure.
Dark Gray Chernozems have the characteristics specified for the order. Virgin soils have a Chernozemic A horizon with a color value darker than 3.5 moist and 4.5 dry. An Ap horizon 10 cm thick must have a color value darker than 3.5 moist and 5 dry. The chroma of the A horizon is usually 1.5 or less, dry. Dark Gray Chernozems may have a light-colored Ae horizon 5 cm or less thick provided that the mixed surface horizon (Ap) meets the requirements specified for the great group. Similar soils having a distinct Ae horizon thicker than 5 cm below the Chernozemic A horizon and a Bt horizon are classified as Dark Gray Luvisols.
Orthic Dark Gray Chernozem (O.DGC)
Common horizon sequence: Ahe, Ae, Bm or Btj or Bt, Cca or Ck
The Orthic Dark Gray Chernozem subgroup may be thought of as the central concept of Dark Gray Chernozems. It encompasses the properties specified for the Chernozemic order and the Dark Gray Chernozem great group. Usually Orthic Dark Gray Chernozems have brownish-colored, prismatic B horizons that commonly meet the requirements of a Bt horizon.
Orthic Dark Gray Chernozems are identified by the following properties:
- They have a Chernozemic A horizon with a color value darker than 3.5 moist and 3.5-4.5 dry for virgin soils (3.5-5 dry for Ap).
- They have a B horizon (Bm, Btj, Bt) at least 5 cm thick that does not contain alkaline earth carbonates.
- They lack an Ae horizon more than 5 cm thick.
- They lack a Bnjtj horizon or a similar horizon characteristic of intergrades to the Solonetzic order.
- They lack evidence of gleying as indicated by faint to distinct mottling within 50 cm of the mineral surface.
Rego Dark Gray Chernozem (R.DGC)
Common horizon sequence: Ah or Ahe, Cca or Ck
These soils have the general properties specified for the Chernozemic order and the Dark Gray Chernozem great group. They differ from Orthic Dark Gray Chernozems either in lacking a B horizon or in having a B horizon (Bm) less than 5 cm thick. Usually Rego Dark Gray Chernozems have an AC profile. They may also have saline features.
Calcareous Dark Gray Chernozem (CA.DGC)
Common horizon sequence: Ah, Ahe, Bmk, Cca or Ck
These soils have the general properties of the Chernozemic order and the Dark Gray Chernozem great group. They differ from Orthic Dark Gray Chernozems by having a B horizon from which primary alkaline earth carbonates have not been removed completely (Bmk). Otherwise they have the general properties of Orthic Dark Gray Chernozems.
Solonetzic Dark Gray Chernozem (SZ.DGC)
Common horizon sequence: Ahe, Ae, Bnjtj, Cs or Ck
These soils have the general properties specified for the Chernozemic order and the Dark Gray Chernozem great group. They differ from Orthic Dark Gray Chernozems by having properties indicative of intergrading to the Solonetzic order. Specifically, they have either a Bnj, Bnjtj, or Btnj horizon, and they may have Ae, AB, and saline C horizons. The Ae horizon, if present, is not more than 5 cm thick. The B horizon usually has prismatic structure and hard consistence, and the prisms usually break to blocky secondary structural units with shiny, dark coatings. Solonetzic Dark Gray Chernozems are usually associated with saline materials. Thus, their B horizons usually have a higher proportion of exchangeable Na or Na and Mg than is characteristic of Orthic Dark Gray Chernozems.
Vertic Dark Gray Chernozem (V.DGC)
Common horizon sequence: Ah or Ahk, Ae or Aej, Bm or Bmk, Btj or Bnjtj, Bvj, Bss or Bkss or Ckss Ck
These soils have the general properties specified for the Chernozemic order and the Dark Gray Chernozem great group. Theymay have any horizons in the upper solum common to other subgroups within the Dark Gray Chernozem great group. However, they differ from other subgroups by having properties indicative of intergrading to the Vertisolic order. Specifically, they have a slickenside horizon (Bss, Bkss or Ckss), the upper boundary of which occurs within 1 m of the mineral soil surface. As well, they may have a weak vertic horizon (Bvj or BCvj).
Gleyed Dark Gray Chernozem (GL.DGC)
Common horizon sequence: Ahe, Bmgj, Ckgj
These soils have the general properties specified for the Chernozemic order and the Dark Gray Chernozem great group. They differ from Orthic Dark Gray Chernozems by having faint to distinct mottles indicative of gleying within 50 cm of the mineral surface.
Gleyed Rego Dark Gray Chernozem (GLR.DGC)
Common horizon sequence: Ahe, Ckgj
These soils have the general properties specified for the Chernozemic order and the Dark Gray Chernozem great group. They differ from Rego Dark Gray Chernozems by having mottles indicative of gleying. Gleyed Rego Dark Gray Chernozems lack a B horizon at least 5 cm thick and have faint to distinct mottles within 50 cm of the mineral surface.
Gleyed Calcareous Dark Gray Chernozem (GLCA.DGC)
Common horizon sequence: Ahe, Bmkgj, Ckgj
These soils have the general properties specified for the Chernozemic order and the Dark Gray Chernozem great group. They differ from Calcareous Dark Gray Chernozems by having mottles indicative of gleying. Gleyed Calcareous Dark Gray Chernozems have a Bmk horizon at least 5 cm thick and faint to distinct mottles within 50 cm of the mineral surface.
Gleyed Solonetzic Dark Gray Chernozem (GLSZ.DGC)
Common horizon sequence: Ahe, Ae, Bnjtjgj, Ckgj, Csgj
These soils have the general properties specified for the Chernozemic order and the Dark Gray Chernozem great group. They differ from Solonetzic Dark Gray Chernozems by having mottles indicative of gleying. Gleyed Solonetzic Dark Gray Chernozems have a Bnj or a Btnj horizon and faint to distinct mottles within 50 cm of the mineral surface.
Gleyed Vertic Dark Gray Chernozem (GLV.DGC)
Common horizon sequence: Ah or Ahk, Ae or Aej, Bmgj or Bmkgj, Btjgj or Bnjtjgj, Bgjvj, Bgjss or Bkgjss or Ckgjss, Ckgj or Ckg
These soils have the general properties specified for the Chernozemic order and the Dark Gray Chernozem great group. They also have properties indicative of intergrading to the Vertisolic order. Specifically, they have a slickenside horizon (Bgjss, Bkgjss or Ckgjss), the upper boundary of which occurs within 1 m of the mineral soil surface. As well, they may have a weak vertic horizon (Bgjvj). They differ from Vertic Dark Gray Chernozems by having faint to distinct mottles, indicative of gleying, within 50 cm of the mineral surface.
Note: Diagnostic horizons are underlined.