The land area of Canada (excluding inland waters) is approximately 9 180 000 km2, of which about 1 375 000 km2 (15%) is rock land. The remainder is classified according to the Canadian system of soil classification, which groups soils into sets of classes at 5 levels or categories from most general to most specific: order, great group, subgroup, family, series. There are 10 orders and several thousand series. Thus the system makes it possible to consider soils at different levels of specificity. Soil classes are defined as specifically as possible to permit uniformity of classification. Limits between classes are arbitrary as there are few sharp divisions of the soil continuum in nature. Differences in soils are the result of the interaction of many factors: CLIMATE, organisms, parent material, relief and time. The soil classification system changes as knowledge grows through soil mapping and research in Canada and elsewhere. Ultimately, all national systems of soil classification should give way to an international system.
The order and its 3 great groups were defined in 1973, after soil and terrain surveys in the Mackenzie Valley yielded new knowledge about the properties, genesis and significance of these soils. Turbic Cryosols have a patterned surface (hummocks, stone nets, etc) and mixed horizons or other evidence of cryoturbation (see PERIGLACIAL LANDFORMS). Static Cryosols lack marked evidence of cryoturbation; they are associated with sandy or gravelly materials. Organic Cryosols are composed dominantly of organic materials (eg, PEAT). Because organic material acts as an insulator, Organic Cryosols occur farther south than the boundary of continuous permafrost.
Organic soils are subdivided into 4 great groups. Fibrisols, common in Canada, consist predominantly of relatively undecomposed organic material with clearly visible plant fragments; resistant fibres account for over 40% by volume. Most soils derived from Sphagnum mosses are Fibrisols. Mesisols are more highly decomposed and contain less fibrous material than Fibrisols (10-40% by volume). Humisols consist mainly of humified organic materials and may contain up to 10% fibre by volume. Folisols consist mainly of thick deposits of forest litter overlying bedrock, fractured bedrock or unconsolidated material. They occur commonly in wet mountainous areas of coastal BC.
The order and its 2 great groups were recognized in the Canadian system in the 1990s after extensive studies of pedons in the Great Plains. The Vertisol great group has a light-coloured A horizon that is not readily distinguishable, and the Humid Vertisol great group has a dark-coloured A horizon enriched in organic matter that is clearly distinguishable from the underlying soil material.
Podzolic soils occupy about 1 429 000 km2 (15.6%) of Canada's land area and are dominant in vast areas of the humid Appalachian and Canadian Shield regions and in the humid coastal region of BC. They are divided among 3 great groups on the basis of the kind of Podzolic B horizon. Humic Podzols have a dark B horizon with a low iron content. They occur mainly in wet sites under humid climates and are much less common than other Podzolic soils.
Ferro-Humic Podzols have a dark reddish brown or black B horizon containing at least 5% organic carbon and appreciable amounts (often 2% or more) of aluminum and iron in organic complexes. They occur commonly in the more humid parts of the area of Podzolic soils; eg, coastal BC and parts of Nfld and southern Québec. Humo-Ferric Podzols, the most common Podzolic soils in Canada, have a reddish brown B horizon containing less than 5% organic carbon associated with aluminum and iron complexes.
Three great groups of Gleysolic soils are defined. Humic Gleysols have a dark A horizon enriched in organic matter. Gleysols lack such a horizon. Luvic Gleysols have a leached (Ae) horizon underlain by a B horizon in which the clay has accumulated; they may have a dark surface horizon.
The 4 great groups of Solonetzic soils are based on properties reflecting the degree of leaching. Solonetz soils have a dark, organic-matter-enriched A horizon overlying the Solonetzic B, which occurs usually at a depth of 20 cm or less. The Ae (grey, leached) horizon is very thin or absent. Solodized Solonetz have a distinct Ae horizon between the dark A and the Solonetzic B. Solods have a transitional AB or BA horizon formed by degradation of the upper part of the Solonetzic B horizon. Vertisolic Solonetzic soils have features intergrading the Vertisolic order in addition to any of the above Solonetzic features. The developmental sequence of Solonetzic soils is commonly from saline parent material to Solonetz, Solodized Solonetz and Solod. As leaching progresses, the salts and sodium ions are translocated downward. If leaching progresses for long enough and salts are removed completely, the Solonetzic B may disintegrate completely. The soil would then be classified in another order. Resalinization may occur and reverse the process associated with leaching.
The 4 great groups of Chernozemic soils are distinguished based upon surface horizon colour, associated with the relative dryness of the soil. Brown soils have brownish A horizons and occur in the driest area of the Chernozemic region. Dark Brown soils have a darker A horizon than Brown soils, reflecting a somewhat higher precipitation and associated higher organic-matter content. Black soils, associated with subhumid climates and tall-grass native vegetation, have a black A horizon which is usually thicker than that of Brown or Dark Brown soils. Dark Gray soils are transitional between grassland Chernozemic soils and the more strongly leached soils of forested regions.
The 2 great groups of Luvisolic soils are distinguished mainly on the basis of soil temperature. Gray Brown Luvisols have an A horizon in which organic matter has been mixed with the mineral material (commonly by earthworm activity), an eluvial horizon (Ae) and an illuvial horizon (Bt). Their mean annual soil temperature is 8°C or higher. The major area of Gray Brown Luvisols is found in the southern part of the Great Lakes-St Lawrence Lowlands. Gray Luvisols have eluvial and illuvial horizons and may have an Ah horizon if the mean annual soil temperature is below 8°C. Vast areas of Gray Luvisols in the Boreal Forest Zone of the Interior Plains have thick, light grey eluvial horizons underlying the forest litter and thick Bt horizons with clay coating the surface of aggregates.
Four great groups are distinguished on the basis of organic matter enrichment in the A horizon and acidity. Melanic Brunisols have an Ah horizon at least 10 cm thick and a pH above 5.5. They occur commonly in southern Ontario and Québec. Eutric Brunisols have the same basic properties as Melanic Brunisols, except that the Ah horizon, if any, is less than 10 cm thick. Sombric Brunisols have an Ah horizon at least 10 cm thick, and are acid and their pH is below 5.5. Dystric Brunisols are acidic and do not have an Ah horizon 10 cm thick.
Families are based on parent material properties and soil climate. For example, the Orthic Gray Luvisol subgroup includes soils of a wide range of texture (gravelly sandy loam to clay), different mineralogy and different temperature and water regimes. The soil family designation is much more specific; eg, Orthic Gray Luvisol, clayey, mixed (mineralogy), cold, subhumid.
Series have a vast array of properties (eg, horizon thickness and colour, gravel content, structure) that fall within a narrow range. Thus, for example, the series name Breton implies all the basic properties of the Luvisolic order, the Gray Luvisol great group, the Orthic Gray Luvisol subgroup and the fine, loamy, mixed, cold subhumid family of that subgroup as well as series-specific properties. A series name implies so much specific information about soil properties that a wide range of interpretations can be made on the probable suitability of the soil for a variety of uses.
Author J.A. MCKEAGUE AND H.B. STONEHOUSE
Links to Other Sites
Soil Landscapes of Canada
This site features photographs of typical soil landscapes found in various regions of Canada. See also the glossary of soil science terminology. From Agriculture and Agri-Food Canada.
Soil Conservation Council of Canada
The Soil Conservation Council of Canada is the face and voice of soil conservation in Canada. Features online articles about soil science and related topics.
What is Permafrost?
This site is an extensive information source about the nature and location of permafrost regions in Canada. Check the menu at the left side of the page for additional maps and data. From the Geological Survey of Canada.
Glossary: Terrain Classification
Glossary of technical terms related to terrain features in the landscape. A Government of British Columbia website.
Glossary: Alberta Soils
A glosssary of terms related to soil conditions and home construction. A Government of Alberta website.
A glossary of terms related to the environment, ecology, and geology. Check the rest of the site for additional information. From the Alberta Online Encyclopedia.
Glossary: Prime and Marginal Agricultural Soils and Landscapes
A bilingual glossary of terms commonly used in the classification of agricultural soils and landscapes. Check other sections of this site for additional information on this topic. From the Government of Ontario.
Canadian Agri-Food Policy Institute
Check out this website for information and reports about current issues impacting on the productivity and competitiveness of Canada's agri-food sector.
Soils of Canada
An extensive information source about the formation, characteristics and distribution of various soil types found in Canada. From the Department of Soil Science, University of Saskatchewan.