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.
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:
- 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.
- It has a color value darker than 5.5 dry and 3.5 moist and has a chroma of less than 3.5 moist.
- It has a color value at least one Munsell unit darker than that of the IC horizon.
- It contains 1-17% organic C and its C:N ratio is less than 17.
- Characteristically it has neither massive structure and hard consistence nor single-grained structure, when dry.
- It has a base saturation (neutral salt) of more than 80% and Ca is the dominant exchangeable cation.
- 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:
- 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).
- 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.
|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.
|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)