Great groups are the first major subdivisions of soil orders. Each great group carries with it the criteria of the order to which it belongs, as well as properties that reflect differences in the strengths of dominant processes, or a major contribution of a process in addition to the dominant one.
For example, if someone describes a Prairie soil as a dark brown chernozem, the order is chernozemic (soils with rich topsoil that developed under grassland vegetation) and the great group is dark brown, which refers to the surface colour of the soil.
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This map shows the major great soil groups in agricultural areas in Western Canada.
It all begins with order
Soil is affected by environment and population influences, causing it to form specific and recognizable layers called horizons.
Soil scientists use horizons to classify soils into hierarchical categories. The major levels used in soil classification include its order, great group and subgroup.
The system has been modified over time, with the last major addition in 1996, when the vertisolic order was added to the system.
There are 10 soil orders in the Canadian system of soil classification:
1. Chernozemic: A grassland soil formed by high levels of organic matter from grass roots.
2. Solonetzic: A grassland soil with high sodium levels; usually clay-rich and often with saline material.
3. Podzolic: A forest soil normally found in coniferous areas. High soil acidity results in the formation of bleached layers and iron and aluminum deposits in other layers.
4. Luvisolic: The soil is derived from underlying sedimentary rocks or clay lacustrine (glacial lake) deposits. They are relatively high in clay, calcium and magnesium. These soils typically have neutral or alkaline pH values, although there are some acidic luvisols, especially in Eastern Canada.
5. Brunisolic: A forest soil with properties not strongly enough developed to meet the criteria for luvisolic or podzolic.
6. Gleysolic: Found wherever temporary or permanent water saturation cause formation of gleyed features in the profile.
7. Regosolic: Found throughout Canada wherever pedogenic conditions prevent the formation of B horizons (unstable slopes, sand dunes, flood plains etc.).
8. Vertisolic: Associated with high clay glacio-lacustrine (glacial lake) landscapes; characterized by shrinking and swelling of clays.
9. Cryosolic: A soil of arctic and tundra regions; characterized by presence of permafrost.
10. Organic: Organic soils are associated with the accumulation of organic materials (peat) in water-saturated conditions. They are most commonly associated with boreal forest soils.
Terms
Calcification: Processes leading to accumulation of CaC03 in a horizon.
Decalcification: Reactions that remove calcium carbonate (CaC03) from a horizon.
Decomposition: Breakdown and loss of minerals and soil organic matter.
Desalinization: Removal of soluble salts in a horizon.
Desilication: Chemical migration of silica out of the solum leaving iron and aluminum minerals behind.
Eluviation: Movement of material out of a soil horizon by suspension in or dissolution by water.
Gley, gleization: Water saturation leads to oxygen depletion in soil and causes trace metals such as iron, manganese and lead to change colour within each soil layer. Oxidized iron has a reddish colour; oxygen-depleted iron takes on a blue-grey hue and dominates the colour of the horizon. If the iron becomes concentrated it can re-oxidize, producing reddish or brown mottles. These features are collectively referred to as gley.
Hydric soils: A soil with sustained exposure to water (ex. flooding). Hydric soils have a low oxygen content, leading to elevated concentrations of iron and other elements.
Illuviation: Leaching of material from one soil horizon into another.
Leaching: Removal of soluble material from the soil.
Lessivage: Physical transfer of clay within the solum.
Melanization: Darkening of A horizon material by addition and mixing of soil organic matter.
Mineralization: Release of inorganic material through decomposition of organic matter.
Paludization: Accumulation of organic materials under anaerobic (no oxygen) conditions. Occurs in organic soils.
Pedogenesis: Soil formation. Also known as soil genesis.
Pedoturbation: Physical churning and mixing of soil material.
Podzolization: Chemical migration of iron, aluminum and soil organic matter within the solum.
Salinization: Accumulation of soluble salts in a horizon.
Sesquioxides: An oxide containing three atoms of oxygen and two of another element. Example: aluminum oxide (Al2O3).
Soil processes: Gains, losses, transfers and transformations of organic matter, soluble salts, carbonates, silicate clay minerals, sesquioxides and silica.
Solodization: Leaching of sodium salts from a horizon.
Solonization: Accumulation of sodium salts in a horizon.
Solum: the upper part of the soil profile, which is influenced by plant roots; the A horizon and the B horizon.
SOM: Soil organic matter.
Links to soil classification and soil science in Canada:
