Brown Chernozem (BC)

These are soils that occur in the most arid segment of the climatic range of Chernozemic soils and have brownish-colored A horizons. They are associated with xerophytic and mesophytic grass and forb vegetation. In virgin Brown Chernozems the upper part of the Ah horizon is commonly as light as or lighter in color value than the lower part of the Ah or the upper B horizon.

Brown Chernozems have chernozemic Ah or Ap horizons with color values darker than 3.5 moist and 4.5-5.5 dry. The chroma of the A horizon is usually higher than 1.5. The soil climate of this great group is typically cold, rarely mild, and is subarid to semiarid (see Chapter 14 on soil family).

Orthic Brown Chernozem (O.BC)

Common horizon sequence: Ah, Bm, Cca or Ck

The Orthic Brown Chernozem subgroup may be thought of as the central concept of Brown Chernozems. It encompasses the properties specified for the Chernozemic order and the Brown Chernozem great group. Orthic Brown Chernozems are well drained and their B horizons are usually brown with prismatic macrostructure. The prismatic peds are usually coarse in coarse-textured soils. With increasing clay content, the peds become smaller and have an increasing tendency to crush to fine blocky and granular aggregates. Thin clay coatings occur occasionally to commonly on ped surfaces in the B horizon. A light-colored horizon of carbonate accumulation usually occurs below the brownish B horizon.

Orthic Brown Chernozems are identified by the following properties:

  1. They have a Chernozemic A horizon with a color value darker than 3.5 moist and 4.5-5.5 dry.
  2. They have a B horizon (Bm, Btj, or Bt) at least 5 cm thick that contains no alkaline earth carbonates.
  3. They lack an Ae horizon at least 2 cm thick.
  4. They lack a Bnjtj horizon or a similar horizon characteristic of intergrades to the Solonetzic order.
  5. They lack evidence of gleying as indicated by faint to distinct mottling within 50 cm of the mineral surface.

Orthic Brown Chernozems and all other subgroups of Chernozemic soils may have any of the following features that are separated either at the family or series level taxonomically or as phases of any taxonomic level above the family: lithic, saline, and carbonated.

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Rego Brown Chernozem (R.BC)

Common horizon sequence: Ah, C or Cca,or Ck

These soils have the general properties specified for the Chernozemic order and the Brown Chernozem great group. They differ from Orthic Brown Chernozems either in lacking a B horizon or in having a B horizon (Bm) less than 5 cm thick. Usually Rego Brown Chernozems have an AC profile. They may also have saline features.

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Calcareous Brown Chernozem (CA.BC)

Common horizon sequence: Ah, Bmk, Cca or Ck

These soils have the general properties of the Chernozemic order and the Brown Chernozem great group. They differ from Orthic Brown 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 Brown Chernozems.

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Eluviated Brown Chernozem (E.BC)

Common horizon sequence: Ah, Ae, Btj or Bt, Cca or Ck

These soils have the general properties of the Chernozemic order and the Brown Chernozem great group. They differ from Orthic Brown Chernozems by having an eluvial horizon or horizons at least 2 cm thick (Ahe, Ae, Aej) usually underlain by a weakly to moderately developed illuvial Btj or Bt horizon. Commonly, the eluvial horizon is slightly to moderately acid. Two variations of this subgroup may be recognized.

One variation has pedons in which eluviation is indicated by light-colored, relic, macroprismatic structure below the Ah or Ap. The prismatic units break into coarse to medium platy peds that commonly have vesicular or tubular voids. This structure suggests the development of an eluvial horizon from a former prismatic B. The Bt or Btj horizon underlying the eluvial horizon usually has well-developed macroprismatic structure that breaks to blocky peds of lower color value and slightly higher chroma than the eluvial horizon.

The other variation has cumulic pedons in which the periodic deposition of transported soil materials modifies the normal horizon differentiation caused by leaching. These pedons have thick horizons of partly leached, accumulated materials overlying former A or transitional AB horizons. They are usually found on lower concave slopes where sediments are deposited from upslope. Commonly, such pedons can be recognized by their thick Ahe horizons.

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Solonetzic Brown Chernozem (SZ.BC)

Common horizon sequence: Ah, Ae, Btnj or Btjnj, Csa or Ck

These soils have the general properties specified for the Chernozemic order and the Brown Chernozem great group. They differ from Orthic Brown Chernozems by having properties that indicate intergrading to the Solonetzic order. Specifically, they have a Bnj, Btjnj, or Btnj horizon and may have Ae, AB, and saline C horizons. The B horizon usually has prismatic structure and hard consistence. The prisms usually break to blocky secondary structural units having shiny, dark coatings. The eluvial horizon that is found in some Solonetzic Brown Chernozems may be similar to that described for the Eluviated Brown Chernozem subgroup. Solonetzic Brown Chernozems are usually associated with saline materials, and their B horizons usually have a higher proportion of exchangeable Na or Na and Mg than is characteristic of Orthic Brown Chernozems.

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Vertic Brown Chernozem (V.BC)

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 Brown Chernozem great group. They may have any horizons in the upper solum common to other subgroups within the Brown 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, and may have a weak vertic horizon (Bvj or BCvj).

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Gleyed Brown Chernozem (GL.BC)

Common horizon sequence: Ah, Bmgj, Ckgj

These soils have the general properties specified for the Chernozemic order and the Brown Chernozem great group. They differ from Orthic Brown Chernozems by having faint to distinct mottles indicative of gleying within 50 cm of the mineral surface.

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Gleyed Rego Brown Chernozem (GLR.BC)

Common horizon sequence: Ah,Ckgj

These soils have the general properties specified for the Chernozemic order and the Brown Chernozem great group. They differ from Rego Brown Chernozems by having mottles indicative of gleying. Gleyed Rego Brown Chernozems lack a distinct B horizon at least 5 cm thick and have faint to distinct mottles within 50 cm of the mineral surface.

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Gleyed Calcareous Brown Chernozem (GLCA.BC)

Common horizon sequence: Ah, Bmkgj, Ckgj

These soils have the general properties specified for the Chernozemic order and the Brown Chernozem great group. They differ from Calcareous Brown Chernozems by having mottles indicative of gleying. Gleyed Calcareous Brown Chernozems have a Bmk horizon at least 5 cm thick and faint to distinct mottles within 50 cm of the mineral surface.

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Gleyed Eluviated Brown Chernozem (GLE.BC)

Common horizon sequence: Ah, Aej, Btjgj or Btgj ,Ckgj

These soils have the general properties specified for the Chernozemic order and the Brown Chernozem great group. They differ from Eluviated Brown Chernozems by having mottles indicative of gleying. Gleyed Eluviated Brown Chernozems have an eluvial horizon and faint to distinct mottles within 50 cm of the mineral surface.

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Gleyed Solonetzic Brown Chernozem (GLSZ.BC)

Common horizon sequence: Ah,Ae, Bnjtjgj, Csagj

These soils have the general properties specified for the Chernozemic order and the Brown Chernozem great group. They differ from Solonetzic Brown Chernozems by having mottles indicative of gleying. Gleyed Solonetzic Brown Chernozems have a Bnj or a Btnj horizon and faint to distinct mottles within 50 cm of the mineral surface.

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Gleyed Vertic Brown Chernozem (GLV.BC)

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 Brown Chernozem great group. They also have properties that indicate 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, and may have a weak vertic horizon (Bgjvj). They differ from Vertic Brown Chernozems by having faint to distinct mottles, indicative of gleying, within 50 cm of the mineral surface.

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Note: Diagnostic horizons are underlined.