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:
- They have a Chernozemic A horizon with a color value darker than 3.5 moist and 4.5-5.5 dry.
- They have a B horizon (Bm, Btj, or Bt) at least 5 cm thick that contains no alkaline earth carbonates.
- They lack an Ae horizon at least 2 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.
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.
Note: Diagnostic horizons are underlined.