Page 619 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

Chapter 18 The Geography of Soils 583
Canadian scientists needed a taxonomic system based on observable and measurable properties in soils specific to Canada. This meant a departure from Marbut’s 1938 U.S. classification. Canada’s first taxonomic system, the Canadian System of Soil Classification (CSSC), was intro- duced in 1955, splitting away from the soil classification effort in the United States. Classification work progressed through the Canada Soil Survey Committee after 1970 and was replaced by the Expert Committee on Soil Survey in 1978, all under the purview of Agriculture Canada. This committee worked on interpretation, mapping systems, soil degradation, and soil classification and produced the second edition of the Canadian System of Soil Classifica- tion in 1987. Work continued with the classification of Vertisols and further development of the CSSC. The third edition of the Canadian System of Soil Classification was published in 1998. In the U.S., classification reform culmi- nated in the Soil Taxonomy introduced in 1975.
The Canadian System of Soil Classification provides taxa for all soils presently recognized in Canada and is adapted to Canada’s expanses of forest, tundra, prairie, frozen ground, and colder climates. As in the U.S. Soil Taxonomy system, the CSSC classifications are based on observable and measurable properties found in real soils that may result from the interactions of genetic pro- cesses rather than idealized soils. The system is flexible in that its framework can accept new findings and infor- mation in step with progressive developments in the soil sciences.
Categories of Classification in the CSSC
Categorical levels are at the heart of a taxonomic sys- tem. These categories are based on soil profile properties organized at five levels, nested in a hierarchical pattern to permit generalization at several levels of detail. Each level is referred to as a category of classification. The levels in the CSSC are briefly described here, as adapted from the third edition of The Canadian Soil Classification System.
• Order: Each of 10 soil orders has pedon properties that reflect the soil environment and effects of active soil- forming processes.
• Great group: Subdivisions of each order reflect differ- ences in the dominant processes or other major con- tributing processes. As an example, in Luvic Gleysols (great group name followed by order) the dominant pro- cess is gleying—reduction of iron and other minerals— resulting from poor drainage under either grass or forest cover with Aeg and Btg horizons (see Table 18.1).
• Subgroup: Subgroups are differentiated by the content and arrangement of horizons that indicate the relation of the soil to a great group or order or the subtle transi- tion toward soils of another order.
• Family: This is a subdivision of a subgroup. Parent material characteristics such as texture and mineralogy, soil climatic factors, and soil reactions are important.
• Series: Detailed features of the pedon differentiate sub- divisions of the family—the essential soil-sampling
unit. Pedon horizons fall within a narrow range of colour, texture, structure, consistence, porosity, mois- ture, chemical reaction, thickness, and composition.
Soil Horizons in the CSSC
Soil horizons are named and standardized as diagnostic in the classification process. Several mineral and organic horizons and layers are used in the CSSC. Three mineral horizons are recognized by capital letter designation, fol- lowed by lowercase suffixes for further description. Prin- cipal soil-mineral horizons and suffixes are presented in Table 18.1.
Four organic horizons are identified in the Canadian classification system. O is further defined through sub- horizon designations. Note that for organic soils, such layers are identified as tiers. These organic horizons are detailed in Table 18.2.
The 10 Soil Orders of the CSSC
At the heart of the Canadian System of Soil Classifica- tion are 10 general orders. These orders were developed specifically for soils in Canada and are presented here with their associated great groups and subgroups. The 10 orders of the CSSC, and related great groups, are sum- marized below with a general description of properties, related great groups, an estimated percentage of land area for the soil order, a fertility assessment, and any appli- cable soil taxonomy equivalent. Figure 18.11 is a gener- alized map of the soil landscapes of Canada. This map illustrates the great variation of soils across the country.
The Soil Landscapes of Canada (SLC) site at sis.agr .gc.ca/cansis/ provides a useful assortment of landscape and soil profile photographs, arranged geographically across Canada from east to west. The site also has an interactive GIS online mapping application. Version 2.2 SLC Component Mapping (December 1996) is operational and involves the CSSC and the Canadian Land Resource Network (CLRN). The component mapping involves a GIS model consisting of layers that include the major charac- teristics of soil and land for all of Canada. You can select a spatial area and a variety of attributes to display on the map (drainage class, soil type, rooting depth, local sur- face form, slope, and vegetation cover, among others).
CRITICAlthinking 18.2 Soil Observations
Select a small soil sample from your campus or an area near where you live. Based on the sections in this chapter on soil characteristics, properties, and formation, describe the sample as completely as you can. Using the general soil map and any other sources available (e.g., local soil technician, internet, related department on campus), are you able to roughly place this sample in one of the soil orders? •