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Chapter 5: Chernozemic Order

A diagrammatic representation of profiles of some subgroups of the Chernozemic order is given in Figure 29. 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.

Figure 29 Diagrammatic horizon pattern of some subgroups of the Chernozemic order.

Figure 29 is a Diagrammatic horizon pattern of some subgroups of the Chernozemic order. 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. Rego Dark Brown Chernozem (R.DBC) Common horizon sequence: Ah, C, Cca or Ck. These soils have the general properties specified for the Chernozemic order and the Dark Brown Chernozem great group. They differ from Orthic Dark Brown Chernozems either in lacking a B horizon or in having a B horizon (Bm) less than 5 cm thick. Usually Rego Dark Brown Chernozems have an AC profile. They may also have saline features. Rego Black Chernozem (R.BLC) Common horizon sequence: Ah, Cca or Ck. These soils have the general properties specified for the Chernozemic order and the Black Chernozem great group. They differ from Orthic Black Chernozems either in lacking a B horizon or in having a B horizon (Bm) less than 5 cm thick. Usually Rego Black Chernozems have an AC profile. They may also have saline features. 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 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. Calcareous Dark Brown Chernozem (CA.DBC) Common horizon sequence: Ah, Bmk, Cca or Ck. These soils have the general properties specified for the Chernozemic order and the Dark Brown Chernozem great group. They differ from Orthic Dark 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 Dark Brown Chernozems. Calcareous Black Chernozem (CA.BLC) Common horizon sequence: Ah, Bmk, Cca or Ck. These soils have the general properties of the Chernozemic order and the Black Chernozem great group. They differ from Orthic Black 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 Black Chernozems. 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. 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. Orthic Dark Brown Chernozem (O.DBC) Common horizon sequence: Ah, Bm, Cca or Ck. The Orthic Dark Brown Chernozem subgroup may be thought of as the central concept of Dark Brown Chernozems. It encompasses the properties specified for the Chernozemic order and the Dark Brown Chernozem great group. Usually, Orthic Dark Brown Chernozems have brownish-colored, prismatic B horizons, and light-colored horizons of carbonate accumulation similar to those of Orthic Brown Chernozems. Orthic Dark 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 between 3.5-4.5 dry. 2. They have a B horizon (Bm, Btj, Bt) at least 5 cm thick that does not contain 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 Black Chernozem (O.BLC) Common horizon sequence: Ah, Bm Cca or Ck. The Orthic Black Chernozem subgroup may be thought of as the central concept of Black Chernozems. It encompasses the properties specified for the Chernozemic order and the Black Chernozem great group. Usually Orthic Black Chernozems have brownish-colored, prismatic B horizons, and light-colored horizons of carbonate accumulation similar to those of Orthic Brown Chernozems. Orthic Black Chernozems are identified by the following properties: 1. They have a Chernozemic A horizon with a color value darker than 3.5 moist and dry. 2. They have a B horizon (Bm, Btj, Bt) at least 5 cm thick that does not contain alkaline earth carbonates. 3. They lack an eluvial horizon (Ahe, Ae, Aej) at least 2 cm thick. 4. They lack a Bnjtj or 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. 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. Eluviated Dark Brown Chernozem (E.DBC) Common horizon sequence: Ah, Ae, Btj or Bt, Cca, Ck. These soils have the general properties specified for the Chernozemic order and the Dark Brown Chernozem great group. They differ from Orthic Dark Brown Chernozems by having an eluvial horizon or horizons (Ahe, Ae, Aej) at least 2 cm thick usually underlain by a weakly to moderately developed illuvial Btj or Bt horizon. Two variations of this subgroup may be recognized. The first has an eluvial horizon developed in a former B horizon. The second has an eluvial horizon developing in an A horizon subject to periodic deposition of sediment. These variations are described in more detail for the Eluviated Brown Chernozem subgroup. Eluviated Black Chernozem (E.BLC) Common horizon sequence: Ah, Ae, Btj, or Bt, Cca or Ck. These soils have the general properties of the Chernozemic order and the Black Chernozem great group. They differ from Orthic Black 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. 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. Solonetzic Dark Brown Chernozem (SZ.DBC) Common horizon sequence: Ah, Ae, Btnj or Btjnj, Csa or Ck. These soils have the general properties specified for the Chernozemic order and the Dark Brown Chernozem great group. They differ from Orthic Dark Brown Chernozems by having properties indicative of 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 with hard consistence. The prisms usually break to blocky secondary structural units having shiny, dark coatings. The eluvial horizon that occurs in some Solonetzic Dark Brown Chernozems may be similar to that described for the Eluviated Dark Brown Chernozem subgroup. Solonetzic Dark Brown 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 Brown Chernozems. Solonetzic Black Chernozem (SZ.BLC) Common horizon sequence: Ah, Ae, Btnj, or Btjnj, Cs or Ck. These soils have the general properties specified for the Chernozemic order and the Black Chernozem great group. They differ from Orthic Black Chernozems by having properties indicative of 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 with shiny, dark coatings. The eluvial horizon that occurs in some Solonetzic Black Chernozems may be similar to that described for the Eluviated Black Chernozem subgroup. Solonetzic Black 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 Black Chernozems. 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: 1. 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). 2. They have a B horizon (Bm, Btj, Bt) at least 5 cm thick that does not contain alkaline earth carbonates. 3. They lack an Ae horizon more than 5 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. 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 .

The general concept of the Chernozemic order is that of well to imperfectly drained soils having surface horizons darkened by the accumulation of organic matter from the decomposition of xerophytic or mesophytic grasses and forbs representative of grassland communities or of grassland-forest communities with associated shrubs and forbs. The major area of Chernozemic soils is the cool, subarid to subhumid Interior Plains of Western Canada. Minor areas of Chernozemic soils occur in some valleys and mountain slopes in the Cordilleran Region extending in some cases beyond the tree line. Most Chernozemic soils are frozen during some period each winter and their sola are dry at some period each summer. Their mean annual soil temperature is >0°C but usually less than 5.5°C. However, some Chernozemic soils in dry valleys of British Columbia have higher temperatures.

The specific definition is as follows: soils of the Chernozemic order have an A horizon in which organic matter has accumulated (Ah, Ahe, Ap) and that meets the requirements of a chernozemic A horizon. A chernozemic A horizon has the following properties:

  1. It is at least 10 cm thick or is thick and dark enough to provide 10 cm of surface material that meets the color criteria given in 2 and 3.
  2. It has a color value darker than 5.5 dry and 3.5 moist and has a chroma of less than 3.5 moist.
  3. It has a color value at least one Munsell unit darker than that of the IC horizon.
  4. It contains 1-17% organic C and its C:N ratio is less than 17.
  5. Characteristically it has neither massive structure and hard consistence nor single-grained structure, when dry.
  6. It has a base saturation (neutral salt) of more than 80% and Ca is the dominant exchangeable cation.
  7. It is restricted to soils having a mean annual soil temperature of 0°C or higher and a soil moisture regime subclass drier than humid. Chernozemic soils may have an Ae horizon and a Bm or a Bt horizon.

They do not have any of the following: solonetzic B, podzolic B, evidence of gleying strongly enough expressed to meet the criteria of Gleysolic soils, or permafrost within 2 m of the surface.

Distinguishing Chernozemic Soils from Soils of Other Orders

Throughout the major area of Chernozemic soils in Canada there is little difficulty in distinguishing them from soils of other orders. However, soils of several other orders may have dark-colored Ah horizons. The bases for distinguishing Chernozemic soils from such soils are outlined below.

Solonetzic These soils have a solonetzic B horizon, but Chernozemic soils do not.

Luvisolic Some Dark Gray Luvisolic and some Chernozemic soils have all of the following: a chernozemic A horizon, an Ae horizon, a Bt horizon, and a subhumid soil moisture regime. The classification of these soils at the order level is done according to these guidelines:

  1. If the chernozemic A horizon is eluviated as evidenced by gray streaks and splotches when the soil is dry, and if the Ae extends to a depth of at least 5 cm below the overlying Ah, Ahe, or Ap horizon, the soil is Luvisolic (Dark Gray Luvisol).
  2. If the chernozemic A is not eluviated as described above, the soil is classified as Chernozemic unless the Ae horizon has a dry color value higher than 5 and a thickness greater than that of the Ah. In the latter case, the soil is classified as Luvisolic (Dark Gray Luvisol).

Podzolic These soils have a podzolic B horizon, but Chernozemic soils do not.

Brunisolic Brunisolic soils having dark-colored, mineral-organic surface horizons do not have a chernozemic A horizon either because their mean annual soil temperature is below 0°C, or because their soil moisture regime is humid or wetter, or the A horizon is acid or has a high C:N ratio. However, a degree of ambiguity remains with respect to the separation of some Melanic Brunisols from Chernozemic soils, especially in subalpine and alpine areas. Further work on these soils may disclose definitive differences between their A horizons and those of Chernozemic soils (see Chapter 4, Brunisolic order).

Regosolic These soils do not have a chernozemic A horizon.

Gleysolic Some of these soils have a chernozemic A horizon. They are excluded from the Chernozemic order because of evidence of reduction and poor drainage as specified in the Gleysolic order definition.

Vertisolic Some Chernozemic soils have a slickenside horizon but Vertisolic soils have both a vertic horizon and a slickenside horizon. Chernozemic soils do not.

Chernozemic soils are divided into four great groups: Brown Chernozem, Dark Brown Chernozem, Black Chernozem, and Dark Gray Chernozem mainly based on the color of the chernozemic A horizon, which reflects differences in the nature and amount of organic matter incorporated with the mineral material because of differences in climate and vegetation. The basis for great group separations are tabulated in the Chernozemic order chart.

Chernozemic Order
  Brown Chernozem Dark Brown Chernozem Black Chernozem Dark Gray Chernozem
Diagnostic horizons are underlined
Ah or Ap horizon present present present present
Color value (dry) 4.5-5.5 3.5-4.5 <3.5 3.5-4.5 (Ap 3.5-5)
Chroma (dry) usually >1.5 usually >1.5 usually ≤1.5 usually ≤1.5
Climate subarid to semiarid semiarid subhumid subhumid

Subgroups are separated based on the kind and sequence of the horizons indicating conformity with the central concept of the great group or intergrades to soils of other orders, or additional features. Some of the former subgroup features (carbonated, saline, and lithic) are now recognized taxonomically at either the family or series level. They may be indicated also as phases of subgroups, great groups, or orders. Features formerly referred to as Grumic are now recognized at either the order level (Vertisolic soils) or at the subgroup level (Vertic intergrades). The former Solonetzic and Solodic subgroups are now combined into a single subgroup Solonetzic, which includes all the intergrades to the Solonetzic order.

Great Group Subgroup
Brown Chernozem Orthic Brown Chernozem O.BC
Rego Brown Chernozem R.BC
Calcareous Brown Chernozem CA.BC
Eluviated Brown Chernozem E.BC
Solonetzic Brown Chernozem SZ.BC
Vertic Brown Chernozem V.BC
Gleyed Brown Chernozem GL.BC
Gleyed Rego Brown Chernozem GLR.BC
Gleyed Calcareous Brown Chernozem GLCA.BC
Gleyed Eluviated Brown Chernozem GLE.BC
Gleyed Solonetzic Brown Chernozem GLSZ.BC
Gleyed Vertic Brown Chernozem GLV.BC
Dark Brown Chernozem Subgroups the same as for Brown Chernozem except for the great group name.
Black Chernozem Subgroups the same as for Brown Chernozem except for the great group name.
Dark Gray Chernozem Orthic Dark Gray Chernozem O.DGC
Rego Dark Gray Chernozem R.DGC
Calcareous Dark Gray Chernozem CA.DGC
Solonetzic Dark Gray Chernozem SZ.DGC
Vertic Dark Gray Chernozem V.DGC
Gleyed Dark Gray Chernozem GL.DGC
Gleyed Rego Dark Gray Chernozem GLR.DGC
Gleyed Calcareous Dark Gray Chernozem GLCA.DGC
Gleyed Solonetzic Dark Gray Chernozem GLSZ.DGC
Gleyed Vertic Dark Gray Chernozem GLV.DGC

Source: The Canadian System of Soil Classification (Third Edition)

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