Chapter 8: Luvisolic Order
A diagrammatic representation of profiles of some subgroups of the Luvisolic order is shown in Figure 33. 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.
Soils of the Luvisolic order generally have light-colored, eluvial horizons and have illuvial B horizons in which silicate clay has accumulated. These soils develop characteristically in well to imperfectly drained sites, in sandy loam to clay, base-saturated parent materials under forest vegetation in subhumid to humid, mild to very cold climates. Depending on the combination of soil environmental factors, some Luvisolic soils occur under conditions outside the range indicated as characteristic. For example, some Luvisolic soils develop in acid parent materials and some occur in forest-grassland transition zones.
Luvisolic soils occur from the southern extremity of Ontario to the zone of permafrost and from Newfoundland to British Columbia. The largest area of these soils occurs in the central to northern Interior Plains under deciduous, mixed, and coniferous forest. The Gray Luvisols of that area usually have well-developed, platy Ae horizons of low chroma, Bt horizons with moderate to strong prismatic or blocky structures, calcareous C horizons, and sola of high base saturation (neutral salt extraction). Gray Luvisols of the Atlantic Provinces commonly have Bt horizons of weak structure and low to moderate base saturation. The Gray Brown Luvisols of southern Ontario and some valleys of British Columbia characteristically have forest-mull Ah horizons, moderate to strong blocky structured Bt horizons, and calcareous C horizons.
Luvisolic soils have an eluvial and Bt horizon as defined. The Bt horizon must have the specified increase in clay over that in the eluvial horizon, clay skins indicative of translocated clay accounting for 1% or more of the area of a section through the horizon, and be at least 5 cm thick. Luvisolic soils may have Ah, Ahe, or dark-colored Ap horizons that satisfy one or more of the following conditions:
- The dark-colored A horizon does not meet the requirements of a chernozemic A.
- The dark-colored A horizon is underlain by a thicker, light-colored Ae horizon that extends to a depth of 15 cm from the mineral surface.
- The dark-colored A horizon shows evidence of eluviation (Ahe or Ap) and is underlain by an Ae horizon at least 5 cm thick.
- If the soil moisture regime is humid or wetter, the dark-colored A horizon may be of any kind.
Luvisolic soils have none of the following: a solonetzic B horizon, a podzolic B horizon if the upper boundary of the Bt horizon is at a depth of more than 50 cm from the mineral surface, evidence of gleying strong enough to meet the requirements of the Gleysolic order, organic horizons thick enough to meet the requirements of the Organic order, or permafrost within 1 m of the mineral surface and 2 m if the soils are cryoturbated.
The genesis of Luvisolic soils is thought to involve the suspension of clay in the soil solution near the soil surface, downward movement of that clay with the soil solution, and the deposition of the translocated clay at a depth where downward movement of the soil solution ceases or becomes very slow. Commonly, the subhorizon of maximum clay accumulation occurs above a Ck horizon. The eluvial horizon (Ahe, Ae) commonly has platy structure due perhaps to the periodic formation of ice lenses. Any condition that promotes dispersion of clay in the A horizons and deposition of this clay in a discrete subsurface horizon favors the development of Luvisolic soils.
Distinguishing Luvisolic Soils from Soils of Other Orders
Guidelines for distinguishing Luvisolic soils from soils of other orders with which they might be confused follow.
Chernozemic Some Chernozemic soils have Ah, Ae, and Bt horizons as do some Luvisolic soils. A basis of differentiation of these soils is the nature of the Ah and Ae horizons as follows:
- If the Ah is not a chernozemic A, the soil is Luvisolic.
- If the soil has a chernozemic A and a light-colored Ae that is thicker than the Ah or Ap and extends to a depth below 15 cm, the soil is Luvisolic.
- If the soil has an eluviated, dark-colored A horizon (Ahe or Ap) and a distinct Ae horizon thicker than 5 cm or that extends below the Ap, it is Luvisolic.
Solonetzic Solonetzic soils have a solonetzic B horizon, but Luvisolic soils do not.
Podzolic Some soils have both a podzolic B and a Bt horizon. The soil is classified as Luvisolic if the upper boundary of the Bt horizon is within 50 cm of the mineral surface and as Podzolic if the boundary is more than 50 cm below the surface.
Brunisolic Luvisolic soils have a Bt horizon, but Brunisolic soils do not.
Gleysolic Some Gleysolic soils have Ae and Bt horizons, but unlike Luvisolic soils they also have colors of low chroma or prominent mottling indicative of strong gleying.
Vertisolic Some Luvisolic soils have a slickenside horizon but Vertisolic soils have both a vertic and a slickenside horizon. Luvisolic soils do not.
Luvisolic soils are divided into two great groups, Gray Brown Luvisol and Gray Luvisol as shown in the Luvisolic order chart. The latter accounts for most of the area of Luvisolic soils.
Subgroups are separated based on the kind and sequence of horizons indicating conformity with the central concept of the great group or intergrades to soils of other orders, or additional features. The former subgroup features turbic, cryic, 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.
| Luvisolic Order | ||
|---|---|---|
| Gray Brown Luvisol | Gray Luvisol | |
| A horizon | forest-mull Ah | may or may not have Ah |
| B horizon | eluvial and Bt horizons | eluvial and Bt horizons |
| Mean annual soil temperature | ≥8°C | usually <8°C |
Gray Brown Luvisol
Soils of this great group have a forest mull Ah horizon and eluvial and Bt horizons as indicated for the order. They occur typically under deciduous or mixed forest vegetation on calcareous materials in areas of mild, humid climate. They occur mainly in the St. Lawrence Lowland.
Under undisturbed conditions the soils may have thin L, F, and H horizons, but, because of high biological activity and the abundance of earthworms, the leaf litter is usually quickly incorporated into the soil and humified. A transitional AB or BA horizon having gray coatings on structural aggregates is generally present, particularly in medium and fine-textured soils. Although the Bt horizon is generally immediately underlain by calcareous materials, a transitional BC horizon may be present.
Under cultivated conditions the Ah and commonly part of the Ae horizon are mixed to form an Ap horizon. However the Bt and part of the Ae horizon usually remain intact under the Ap horizon unless either cultivation greatly exceeds 15 cm in depth or surface erosion has caused the Ap horizon to be developed in the Ae or Bt horizons or both.
Gray Brown Luvisols have either a forest-mull Ah horizon more than 5 cm thick or a dark-colored Ap horizon, an eluvial horizon, and a Bt horizon. The mean annual soil temperature is 8°C or higher and the soil moisture regime is humid or wetter.
The great group is divided into eight subgroups based on the profile developed above the Bt horizon, the presence of Vertic features, and evidence of gleying.
Orthic Gray Brown Luvisol (O.GBL)
Common horizon sequence: Ah, Ae, Bt, Ck
These soils have the properties specified for the Luvisolic order and the Gray Brown Luvisol great group. They have well-developed Ah, eluvial, and Bt horizons, and usually calcareous C horizons. Faint mottling may occur immediately above or within the Bt horizon.
Orthic Gray Brown Luvisols are identified by the following properties:
- These soils have either a forest-mull Ah horizon more than 5 cm thick or a dark-colored (moist) Ap horizon.
- These soils have an Ae horizon of which the upper 5 cm is light colored with a chroma of 3 or less. The difference in chroma between the upper and lower part of the Ae is less than 1.
- These soils have a Bt horizon and lack a Bf horizon.
- Distinct mottling indicative of gleying does not occur within 50 cm of the mineral surface, and prominent mottling does not occur at depths of 50-100 cm.
Brunisolic Gray Brown Luvisol (BR.GBL)
Common horizon sequence: Ah, Ae, Bm or Bf, Ae, Bt, BC, Ck
These soils have the properties specified for the Luvisolic order and the Gray Brown Luvisol great group. They differ from Orthic Gray Brown Luvisols by having in the upper solum either a Bm horizon at least 5 cm thick with a chroma of 3 or more, or a Bf horizon less than 10 cm thick that does not extend below 15 cm. Such Bm or Bf horizons are thought to have developed in a former Ae horizon. If disturbance results in the Bm or Bf horizon being incorporated into the Ap, the disturbed soil is classified as an Orthic Gray Brown Luvisol.
Podzolic Gray Brown Luvisol (PZ.GBL)
Common horizon sequence: LFH, Ah, Ae, Bf, Ae, Bt, BC, Ck
These soils have the properties specified for the Luvisolic order and the Gray Brown Luvisol great group. They differ from Orthic Gray Brown Luvisols by having a Bf horizon at least 10 cm thick in the upper solum. These soils may or may not have an Ae horizon. The upper boundary of the Bt horizon must be within 50 cm of the mineral surface or the soil is classified in the Podzolic order. If disturbance results in the Bf horizon being incorporated into the Ap, the disturbed soil is classified as an Orthic Gray Brown Luvisol.
Vertic Gray Brown Luvisol (V.GBL)
Common horizon sequence: Ah, Ae, Bm or Bf, Bt, Bvj, Bss or Ckss, Ck
These soils have the general properties specified for the Luvisolic order and the Gray Brown Luvisol great group. They may have any horizons in the upper solum common to other subgroups within the Gray Brown Luvisol 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 surface. They may have a weak vertic horizon (Bvj).
Gleyed Gray Brown Luvisol (GL.GBL)
Common horizon sequence: Ah, Aegj, Btgj, Ckg
These soils have the properties specified for the Luvisolic order and the Gray Brown Luvisol great group. They differ from Orthic Gray Brown Luvisols by having either distinct mottles that indicate gleying within 50 cm of the mineral surface, or prominent mottles at depths of 50-100 cm. Commonly the matrix colors are of lower chroma than those of associated, well-drained soils. Gleyed Gray Brown Luvisols generally have thicker and darker Ah horizons than well-drained subgroups on similar parent materials. The color and textural differences between the Ae and Bt horizons are generally less marked in the gleyed than in the orthic subgroup.
Gleyed Brunisolic Gray Brown Luvisol (GLBR.GBL)
Common horizon sequence: Ah, Bmgj, Aegj, Btgj, Ckg
These soils have the properties specified for the Luvisolic order and the Gray Brown Luvisol great group. They differ from Brunisolic Gray Brown Luvisols by having either distinct mottles that indicate gleying within 50 cm of the mineral surface, or prominent mottles at depths of 50-100 cm.
Gleyed Podzolic Gray Brown Luvisol (GLPZ.GBL)
Common horizon sequence: Ah, Ae, Bfgj, Aegj, Btgj, Ckg
These soils have the properties specified for the Luvisolic order and the Gray Brown Luvisol great group. They differ from Podzolic Gray Brown Luvisols by having either distinct mottles that indicate gleying within 50 cm of the mineral surface, or prominent mottles at depths of 50-100 cm. Besides a forest-mull Ah horizon, they have a Bf horizon at least 10 cm thick and a gleyed Bt horizon of which the upper boundary is within 50 cm of the mineral surface.
Gleyed Vertic Gray Brown Luvisol (GLV.GBL)
Common horizon sequence: Ah, Ae, Bmgj, or Bfgj, Btgj, Bgjvj, Bgjss or Ckgjss, Ckgj or Ckg
These soils have the general properties specified for the Luvisolic order and the Gray Brown Luvisol great group. Also, they have properties that indicate intergrading to the Vertisolic order. Specifically, they have a slickenside horizon (Bgjss or Ckgjss), the upper boundary of which occurs within 1 m of the mineral surface. These soils may have a weak vertic horizon (Bgjvj). They differ from Vertic Gray Brown Luvisols by having either distinct mottles that indicate gleying within 50 cm of the mineral surface, or prominent mottles at depths of 50-100 cm.
Gray Luvisol
Soils of this great group have eluvial and Bt horizons as specified for the Luvisolic order. They usually have L, F, and H horizons and may have a degraded Ah or Abe horizon that resembles the upper A horizon of Dark Gray Chernozemic soils. Commonly below the Ae horizon they have an AB or BA horizon in which the ped surfaces are grayer than the interiors of peds. The solum of Gray Luvisols is generally slightly to moderately acid but may be strongly acid. The degree of base saturation (neutral salt extraction) is generally high. The parent materials are usually base saturated and commonly calcareous, but some Gray Luvisols have developed in acid materials.
Gray Luvisols occur typically under boreal or mixed forest vegetation and in forest-grassland transition zones in a wide range of climatic areas. Their main area of occurrence is in the subhumid central to northern part of the Interior Plains, but they occur also in humid and perhumid areas of eastern Canada. In the latter climatic area, they occur mainly on medium- to fine-textured parent materials.
Gray Luvisols have eluvial and Bt horizons. Their mean annual soil temperature is usually less than 8°C. If the soil moisture regime is subhumid, any dark-colored A horizon must satisfy one or more of the following conditions:
- It is not a chernozemic A.
- It is underlain by a thicker Ae horizon that extends to a depth greater than 15 cm below the mineral surface.
- It shows evidence of degradation (Ahe) and is underlain by an Ae horizon at least 5 cm thick below the Ahe or Ap horizon.
The great group is divided into 14 subgroups based on the kind and sequence of horizons and evidence of gleying.
Common horizon sequence: LFH, Ae, AB, Bt, C or Ck
These soils have the properties specified for the Luvisolic order and the Gray Luvisol great group. They have well-developed Ae and Bt horizons and usually have organic surface horizons. Faint mottling may occur immediately above or within the Bt horizon.
Orthic Gray Luvisols are identified by the following properties:
- They have an Ae horizon with a chroma of less than 3 unless the chroma of the parent material is 4 or more.
- They have a Bt horizon.
- They lack a Bf horizon.
- They lack a fragipan.
- They may have a dark-colored, mineral-organic surface horizon (Ah or Ahe) less than 5 cm thick.
- They may have an Ap horizon, but its dry color value must be 5 or higher.
- Distinct mottling, that indicates gleying does not occur within 50 cm of the mineral surface. Prominent mottling does not occur at depths of 50-100 cm.
Common horizon sequence: LFH, Ah or Ahe, Ae, Bt, C or Ck
These soils have the properties specified for the Luvisolic order and the Gray Luvisol great group. They differ from Orthic Gray Luvisols by having an Ah or Ahe horizon 5 cm or more in thickness. These horizons generally have eluvial features, such as gray streaks or splotches when dry, or platy structure. In the case of disturbed soils, the dry color value of the Ap horizon is 3.5-5.0 and some of the Ae horizon remains below the Ap. The differentiation of Dark Gray Luvisols from Dark Gray Chernozemic soils was outlined previously in this chapter. Dark Gray Luvisols have a mean annual soil temperature less than 8°C. They may have a Btnj or a Bm horizon above the Bt horizon.
Brunisolic Gray Luvisol (BR.GL)
Common horizon sequence: LFH, Bm or Bf, Ae, Bt, BC, C or Ck
These soils have the properties specified for the Luvisolic order and the Gray Luvisol great group. They differ from Orthic Gray Luvisols by having in the upper solum, either a Bm horizon at least 5 cm thick with a chroma of 3 or more, or a Bf horizon less than 10 cm thick that does not extend below 15 cm. Such Bm or Bf horizons are thought to have developed in a former Ae horizon. These soils do not have a dark-colored Ah or Ahe horizon 5 cm or more in thickness.
Common horizon sequence: LFH, Ae, Bf, Ae, Bt, BC, C or Ck
These soils have the properties specified for the Luvisolic order and the Gray Luvisol great group. They differ from Orthic Gray Luvisols by having a Bf horizon at least 10 cm thick in the upper solum. They may also have a dark-colored Ah or Ahe horizon 5 cm or more in thickness. The upper boundary of the Bt horizon must be within 50 cm of the mineral surface or the soil is classified in the Podzolic order.
Solonetzic Gray Luvisol (SZ.GL)
Common horizon sequence: LFH, Ae, AB, Btnj, BC, C or Csk
These soils have the properties specified for the Luvisolic order and the Gray Luvisol great group. They differ from Orthic Gray Luvisols by having a Btnj horizon that indicates an intergrade to the Solonetzic order. The Btnj horizon usually has a harder consistence, more pronounced coatings on the prismatic or blocky peds, and a lower ratio of exchangeable Ca:Na than the Bt horizons of most Gray Luvisols. This subgroup is associated with saline parent materials. Solonetzic Gray Luvisols do not have an Ah or Ahe horizon 5 cm or more in thickness, and so the surface horizons do not meet the criteria for Dark Gray Luvisols.
Common horizon sequence: LFH, Ahe, Ae, Bt, Btx or BCx, C
These soils have the properties specified for the Luvisolic order and the Gray Luvisol great group. They differ from Orthic Gray Luvisols by having a fragipan either within or below the Bt horizon.
Common horizon sequence: LFH, Ah or Ahe, Ae, AB, Bt or Btnj, Btvj, Btss or Ckss, Ck
These soils have the general properties specified for the Luvisolic order and the Gray Luvisol great group. They may have any horizons in the upper solum common to other subgroups within the Gray Luvisol great group. However, they differ from other subgroups by having properties that indicate intergrading to the Vertisolic order. Specifically, they have a slickenside horizon (Btss or Ckss), the upper boundary of which occurs within 1 m of the mineral surface. They may have a weak vertic horizon (Btvj).
Common horizon sequence: LFH, Ae, Btgj, Cg
These soils have the properties specified for the Luvisolic order and the Gray Luvisol great group. They differ from Orthic Gray Luvisols by having either distinct mottles that indicate gleying within 50 cm of the mineral surface, or prominent mottles at depths of 50-100 cm. Commonly the matrix colors are of lower chroma than those of associated, well-drained soils.
Gleyed Dark Gray Luvisol (GLD.GL)
Common horizon sequence: LFH, Ah or Ahe, Ae, Btgj, Cg or Ckg
These soils have the properties specified for the Luvisolic order and the Gray Luvisol great group. They differ from Dark Gray Luvisols by having either distinct mottles that indicate gleying within 50 cm of the mineral surface, or prominent mottles at depths of 50-100 cm.
Gleyed Brunisolic Gray Luvisol (GLBR.GL)
Common horizon sequence: LFH, Bm or Bf, Aegj, Btgj, BCgj, Cg
These soils have the properties specified for the Luvisolic order and the Gray Luvisol great group. They differ from Brunisolic Gray Luvisols by having either distinct mottles that indicate gleying within 50 cm of the mineral surface, or prominent mottles at depths of 50-100 cm. They do not have Ah or Ahe horizons 5 cm or more in thickness.
Gleyed Podzolic Gray Luvisol (GLPZ.GL)
Common horizon sequence: LFH, Ae, Bf, Aegj, Btgj, BCgj, Cg
These soils have the properties specified for the Luvisolic order and the Gray Luvisol great group. They differ from Podzolic Gray Luvisols by having either distinct mottles that indicate gleying within 50 cm of the mineral surface, or prominent mottles at depths of 50-100 cm. They may have a dark-colored A horizon 5 cm or more in thickness.
Gleyed Solonetzic Gray Luvisol (GLSZ.GL)
Common horizon sequence: LFH, Ae, ABgj, Btnjgj, Cgj or Csag
These soils have the properties specified for the Luvisolic order and the Gray Luvisol great group. They differ from Solonetzic Gray Luvisols by having either distinct mottles that indicate gleying within 50 cm of the mineral surface, or prominent mottles at depths of 50-100 cm. They do not have an Ah or Ahe horizon 5 cm or more in thickness.
Gleyed Fragic Gray Luvisol (GLFR.GL)
Common horizon sequence: LFH, Ahe, Aegj, Btgj, Btxgj, or BCxg, Cg
These soils have the properties specified for the Luvisolic order and the Gray Luvisol great group. They differ from Fragic Gray Luvisols by having either distinct mottles that indicate gleying within 50 cm of the mineral surface, or prominent mottles at depths of 50-100 cm. They may have a dark-colored A horizon 5 cm or more in thickness.
Gleyed Vertic Gray Luvisol (GLV.GL)
Common horizon sequence: LFH, Ah or Ahe, Ae, AB, Btgj, or Btnjgj, Btgjvj, Btgjss or Ckgjss, Ckgj or Ckg
These soils have the general properties specified for the Luvisolic order and the Gray Luvisol great group. They also have properties that indicate intergrading to the Vertisolic order. Specifically, they have a slickenside horizon (Btgjss or Ckgjss), the upper boundary of which occurs within 1 m of the mineral surface. These soils may have a weak Vertic horizon (Btgjvj). They differ from Vertic Gray Luvisols by having either distinct mottles that indicate gleying within 50 cm of the mineral surface, or prominent mottles at depths of 50-100 cm.
