Chapter 12: Solonetzic Order

A diagrammatic representation of profiles of some subgroups of the Solonetzic order is shown in Figure 39. 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 39 Diagrammatic horizon pattern of some subgroups of the Solonetzic order.

Figure 39 is a Diagrammatic horizon pattern of some subgroups of the Solonetzic order.
Brown Solonetz (B.SZ)
Common horizon sequence: Ah, Bn or Bnt, Csk. Soils of this subgroup have a solonetzic B horizon as defined for the Solonetzic order and the properties specified for the Solonetz great group. They are associated with grass and forb vegetation and a subarid to semiarid climate. Areas of these soils often have patchy microrelief caused by differential erosion. The B horizon is exposed in some eroded pits. Plant growth in the eroded pits is usually very sparse.
Brown Solonetzs have either an Ah, Ahe, or Ap horizon with color values higher than 4.5 dry and chromas usually higher than 1.5 dry, or an exposed solonetzic B horizon. They have neither a strongly alkaline (pH of 8.5 or more) A horizon nor faint to distinct mottles that indicate gleying within the upper 50 cm.
Dark Brown Solonetz (DB.SZ)
Common horizon sequence: Ah, Bn or Bnt, Csk. Soils of this subgroup have a solonetzic B horizon as defined for the Solonetzic order and the properties specified for the Solonetz great group. They are associated with mesophytic grasses and forbs in a semiarid climate. Areas of Dark Brown Solonetzs often have patchy microrelief caused by differential erosion of the A horizon. However, bare eroded pits are not as common as in areas of Brown Solonetzs.
Dark Brown Solonetzs have either an Ah, Ahe, or Ap horizon with color values lower than 3.5 moist and 3.5-4.5 dry, or an exposed solonetzic B horizon. Chromas of the surface horizon are usually higher than 1.5 dry. The soils have neither strongly alkaline (pH of 8.5 or more) A horizons nor faint to distinct mottles that indicate gleying within the upper 50 cm.
Black Solonetz (BL.SZ)
Common horizon sequence: Ah, Bnt, Csk. Soils of this subgroup have a solonetzic B horizon as defined for the Solonetzic order and the properties specified for the Solonetz great group. They are associated mainly with the growth of mesophytic grasses and forbs in a subhumid climate. However, they occur also in areas of discontinuous shrub and tree cover with a ground cover of forbs and grasses. The microrelief associated with differential erosion of the A horizon in areas of Brown and Dark Brown Solonetzs occurs rarely in areas of Black Solonetzs.
Black Solonetzs have an Ah, Ahe, or Ap horizon with color values lower than 3.5 moist and dry, and chromas usually less than 2 moist and dry. They have neither a strongly alkaline (pH of 8.5 or more) A horizon nor faint to distinct mottles that indicate gleying within the upper 50 cm.
Alkaline Solonetz (A.SZ)
Common horizon sequence: Ah, Bn, Csk. Soils of this subgroup have a solonetzic B horizon as defined for the Solonetzic order and the properties specified for the Solonetz great group. They are associated with highly saline materials and with mesophytic grasses and forbs that include alkali-tolerant species. The alkaline A horizon may be of any color including brown, black, and gray. Alkaline Solonetzs occupy a minor area and commonly occur in groundwater discharge sites.
Alkaline Solonetzs have a strongly alkaline A horizon (pH of 8.5 or more) and a solonetzic B horizon. They may have faint to distinct mottles that indicate gleying within the upper 50 cm.
Brown Solodized Solonetz (B.SS)
Common horizon sequence: Ah, Ae, Bn or Bnt, Csk. Soils of this subgroup have a solonetzic B horizon as defined for the Solonetzic order and the properties specified for the Solodized Solonetz great group. They are associated with grass and forb vegetation and a subarid to semiarid climate. Areas of this subgroup often have irregular microrelief caused by differential erosion of the A horizons. The eroded pits usually support only a very sparse plant cover.
Brown Solodized Solonetzs have an Ah, Ahe, or Ap horizon with color values higher than 4.5 dry and chromas usually higher than 1.5 dry. They have Ae and solonetzic B horizons as specified for the great group. They do not have faint to distinct mottles that indicate gleying within the upper 50 cm.
Dark Brown Solodized Solonetz (DB.SS)
Common horizon sequence: Ah, Ae, Bn or Bnt, Csk. Soils of this subgroup have a solonetzic B horizon as defined for the Solonetzic order and the properties specified for the Solodized Solonetz great group. They are associated with mesophytic grasses and forbs in a semiarid climate. Areas of Dark Brown Solodized Solonetzs commonly have irregular microrelief caused by differential erosion of the A horizons.
Dark Brown Solodized Solonetzs have an Ah, Ahe, or Ap horizon with color values lower than 3.5 moist and 3.5-4.5 dry and chromas usually higher than 1.5 dry. They have Ae and solonetzic B horizons as specified for the great group. They do not have faint to distinct mottles that indicate gleying within the upper 50 cm.
Black Solodized Solonetz (BL.SS)
Common horizon sequence: Ah, Ae, Bnt or Bn, Csk. Soils of this subgroup have a solonetzic B horizon as defined for the Solonetzic order and the properties specified for the Solodized Solonetz great group. They are associated mainly with mesophytic grass and forb vegetation and a subhumid climate. However, they also occur in areas of discontinuous shrub and tree vegetation with a ground cover of forbs and grasses. Differential erosion of the A horizon, which is common in areas of Brown and Dark Brown Solodized Solonetzs, seldom occurs in these soils.
Black Solodized Solonetzs have an Ah, Ahe, or Ap horizon with color values lower than 3.5 dry and chromas usually lower than 2 dry. They have Ae and solonetzic B horizons as specified for the great group. They do not have faint to distinct mottles that indicate gleying within the upper 50 cm.
Gleyed Gray Solodized Solonetz (GLG.SS)
Common horizon sequence: Ahe, Aegj, Bntgj, Cskg. Soils of this subgroup have a solonetzic B horizon as defined for the Solonetzic order and the properties specified for the Solodized Solonetz great group. They differ from Gray Solodized Solonetzs by having faint to distinct mottles that indicate gleying within 50 cm of the mineral surface.
Brown Solod (B.SO)
Common horizon sequence: Ah, Ae, AB, Bnt, Ck, Csk. Soils of this subgroup have a solonetzic B horizon as defined for the Solonetzic order and the properties specified for the Solod great group. They are associated with grass and forb vegetation and a subarid to semiarid climate. In areas of these soils there is commonly evidence of previously eroded pits, but they are usually shallow and grass covered.
Brown Solods have an Ah, Ahe, or Ap horizon with color values higher than 4.5 dry and chromas usually higher than 1.5 dry. They have Ae, AB or BA, and solonetzic B horizons as specified for the great group. They do not have faint to distinct mottles that indicate gleying within the upper 50 cm.
Dark Brown Solod (DB.SO)
Common horizon sequence: Ahe, Ae, AB, Bnt, Ck, Csk. Soils of this subgroup have a solonetzic B horizon as defined for the Solonetzic order and the properties specified for the Solod great group. They are associated with mesophytic grasses and forbs in a semiarid to subhumid climate. Evidence of former eroded pits is common in areas of these soils, but the depressions are shallow and grass covered.Dark Brown Solods have an Ah, Ahe or Ap horizon with color values lower than 3.5 moist and 3.5-4.5 dry and chromas usually higher than 1.5 dry. They have Ae, AB or BA, and solonetzic B horizons as specified for the great group. They do not have faint to distinct mottles that indicate gleying within the upper 50 cm.
Black Solod (BL.SO)
Common horizon sequence: Ahe, Ae, AB, Bnt, Ck, Csk. Soils of this subgroup have a solonetzic B horizon as defined for the Solonetzic order and the properties specified for the Solod great group. They are associated mainly with mesophytic grasses and forbs in a subhumid climate, but they also occur in areas of thin or discontinuous shrub and tree cover.Black Solods have an Ah, Ahe, or Ap horizon with color values lower than 3.5 dry and chromas usually higher than 1.5 dry. They have Ae, AB or BA, and solonetzic B horizons as specified for the great group. They do not have faint to distinct mottles that indicate gleying within the upper 50 cm.
Gleyed Dark Gray Solod (GLDG.SO)
Common horizon sequence: Ahe, Aegj, ABgj, Bntgj, Cskg. Soils of this subgroup have a solonetzic B horizon as defined for the Solonetzic order and the properties specified for the Solod great group. They differ from Dark Gray Solods by having faint to distinct mottles that indicate gleying within 50 cm of the mineral surface.
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Soils of the Solonetzic order have B horizons that are very hard when dry and swell to a sticky mass of very low permeability when wet. Typically the solonetzic B horizon has prismatic or columnar macrostructure that breaks to hard to extremely hard (when dry) blocky peds with dark coatings. They occur on saline parent materials in some areas of the semiarid to subhumid Interior Plains in association with Chernozemic soils and to a lesser extent with Luvisolic and Gleysolic soils. Most Solonetzic soils are associated with a vegetative cover of grasses and forbs. Although some occur under tree cover, it is thought that the trees did not become established until solodization was well under way.

Solonetzic soils are thought to have developed from parent materials that were more or less uniformly salinized with salts high in sodium. Leaching of salts by descending rainwater presumably results in deflocculation of the sodium-saturated colloids. The peptized colloids are apparently carried downward and deposited in the B horizon. Further leaching results in depletion of alkali cations in the A horizon, which becomes acidic and a platy Ae horizon usually develops. The underlying B horizon usually consists of darkly stained, fused, intact columnar peds. Structural breakdown of the upper part of the B horizon apparently occurs at an advanced stage of development as exchangeable sodium is leached downward. At this stage the solonetzic B usually breaks readily to blocky peds coated with white silicious powder. Complete destruction of the solonetzic B horizon is the most advanced stage of solodization. The rate of evolution through the stages of development depends on the salt content and hydraulic conductivity of the parent material and on the climate.

Most Solonetzic soils in Canada have a neutral to acidic A horizon indicating that some solodization has occurred. Soils with strongly alkaline A horizons, an early stage of Solonetzic soil formation, are uncommon in Canada. As solodization proceeds, the horizons of salt and lime accumulation move downward from the B to the C horizon. In most Solonetzic soils the saturation extract of the C horizon has a conductivity of at least 4 mS cm-1. Solodization is arrested where saline groundwater is within capillary reach of the solum, and resalinization may occur in groundwater discharge areas.

Soils of the Solonetzic order have a solonetzic B horizon (Bn or Bnt). This horizon has columnar or prismatic structure, is hard to extremely hard when dry, and has a ratio of exchangeable Ca to Na of 10 or less. The macrostructural units usually break to form hard to extremely hard blocky peds with dark coatings. Solonetzic soils do not have permafrost within 1 m of the surface, a surface organic layer 60 cm or more in thickness if fibric or 40 cm or more if mesic or humic, a podzolic B horizon, or evidence of gleying strong enough to meet the criteria for Gleysolic soils.

Distinguishing Solonetzic Soils from Soils of Other Orders

Chernozemic Soils having a chernozemic A horizon and a solonetzic B horizon are classified as Solonetzic. However, sometimes the structure and consistence of the Bnt horizons of Solonetzic soils are similar to the Btnj horizons of some Solonetzic subgroups of Chernozemic soils. In borderline cases the ratio of exchangeable Ca to Na determines the classification.

Luvisolic Some Luvisolic soils are similar to Gray and Dark Gray Solods. The soils having a Bnt horizon rather than a Btnj are classified as Solonetzic.

Gleysolic Some soils have solonetzic B horizons, dull colors, and mottling that indicates strong gleying, within 50 cm of the mineral soil surface. These soils are classified as Gleysolic.

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

The Solonetzic order includes four great groups: Solonetz, Solodized Solonetz, Solod, and Vertic Solonetz. They are separated based on the degree of expression of the Ae horizon, the breakdown of the upper part of the B horizon, and the occurrence of Vertic features as indicated in the Solonetzic order chart.

Subgroups are separated on the basis of features indicating different climatic zones as reflected in the color of the A horizon and on the presence or absence of gleying. Lithic features are now recognized taxonomically at the family level or as a phase of subgroups, great groups, or orders.

Solonetzic Order
  Solonetz Solodized Solonetz Solod Vertic Solonetz
Diagnostic horizons are underlined
Ae horizon no continuous Ae ≥2 cm thick Ae ≥2 cm thick Ae ≥2 cm thick any features of Solonetz, Solodized Solonetz, or Solod
B horizon   intact, columnar Bnt or Bn distinct AB or BA (disintegrating Bnt)
Vertic features       slickenside


Great Group Subgroup
Solonetz Brown Solonetz B.SZ
Dark Brown Solonetz DB. SZ
Black Solonetz BL.SZ
Alkaline Solonetz A.SZ
Gleyed Brown Solonetz GLB.SZ
Gleyed Dark Brown Solonetz GLDB.SZ
Gleyed Black Solonetz GLBL.SZ
Solodized Solonetz Brown Solodized Solonetz B.SS
Dark Brown Solodized Solonetz DB.SS
Black Solodized Solonetz BL.SS
Dark Gray Solodized Solonetz DG.SS
Gray Solodized Solonetz G.SS
Gleyed Brown Solodized Solonetz GLB.SS
Gleyed Dark Brown Solodized Solonetz GLDB.SS
Gleyed Black Solodized Solonetz GLBL.SS
Gleyed Dark Gray Solodized Solonetz GLDG.SS
Gleyed Gray Solodized Solonetz GLG.SS
Solod Brown Solod B.SO
Dark Brown Solod DB.SO
Black Solod BL.SO
Dark Gray Solod DG.SO
Gray Solod G.SO
Gleyed Brown Solod GLB.SO
Gleyed Dark Brown Solod GLDB.SO
Gleyed Black Solod GLBL.SO
Gleyed Dark Gray Solod GLDG.SO
Gleyed Gray Solod GLG.SO
Vertic Solonetz Brown Vertic Solonetz B.VSZ
Dark Brown Vertic Solonetz DB.VSZ
Black Vertic Solonetz BL.VSZ
Gleyed Brown Vertic Solonetz GLB.VSZ
Gleyed Dark Brown Vertic Solonetz GLDB.VSZ
Gleyed Black Vertic Solonetz GLBL.VSZ

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