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.
|Gray Brown Luvisol||Gray Luvisol|
|Diagnostic horizons are underlined|
|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||Orthic Gray Brown Luvisol O.GBL|
|Brunisolic Gray Brown Luvisol BR.GBL|
|Podzolic Gray Brown Luvisol PZ.GBL|
|Vertic Gray Brown Luvisol V.GBL|
|Gleyed Gray Brown Luvisol GL.GBL|
|Gleyed Brunisolic Gray Brown Luvisol GLBR.GBL|
|Gleyed Podzolic Gray Brown Luvisol GLPZ.GBL|
|Gleyed Vertic Gray Brown Luvisol GLV.GBL|
|Gray Luvisol||Orthic Gray Luvisol O.GL|
|Dark Gray Luvisol D.GL|
|Brunisolic Gray Luvisol BR.GL|
|Podzolic Gray Luvisol PZ.GL|
|Solonetzic Gray Luvisol SZ.GL|
|Fragic Gray Luvisol FR.GL|
|Vertic Gray Luvisol V.GL|
|Gleyed Gray Luvisol GL.GL|
|Gleyed Dark Gray Luvisol GLD.GL|
|Gleyed Brunisolic Gray Luvisol GLBR.GL|
|Gleyed Podzolic Gray Luvisol GLPZ.GL|
|Gleyed Solonetzic Gray Luvisol GLSZ.GL|
|Gleyed Fragic Gray Luvisol GLFR.GL|
|Gleyed Vertic Gray Luvisol GLV.GL|