Page 632 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

596 part IV Soils, Ecosystems, and Biomes
Cool and moist climate
Humus- rich
Sandy, bleached
Spodic horizon
O Acidic organic litter
Eluviation of
A bases, oxides,
clays; light pale layer
Illuviation of
B oxides and
clays
C Loss of base to water table
Freshly ploughed Podsolic soil near Lakeville, Nova Scotia, being prepared for planting vegetables. Formed beneath coniferous forests, the land is cleared for crops and apple orchards (visible
in the distance).
▲Figure 18.21 Podsolization. [(b) Bobbé Christopherson.]
Cordilleran Region, in parts of the South Boreal Region, and in the cool temperate regions of central Canada. The two great groups of the Vertisolic order are Vertisol and Humic Vertisol, and these contain six subgroups.
CSSC and Worldwide Soil Taxonomy
Numerous systems of soil taxonomy exist in many coun- tries throughout the world. The Canadian System of Soil Classification was designed to classify the soils that exist in Canada, whether or not the soils are likely to be cul- tivated. The CSSC system was not designed to be a com- prehensive system to classify the world’s soils. Other systems are more useful in the countries where the sys- tems were developed. The FAO–UNESCO Soil Map of the World is helpful for correlating the different soil classifi- cations in use. (See www.itc.nl/~rossiter/research/rsrch_ss_class .html#FAO.)
Perhaps the closest to a comprehensive system is the Soil Taxonomy of the Natural Resources Con- servation Service (NRCS) in the United States, a sys- tem under development since 1951, and implemented in 1975. The Soil Taxonomy is of major influence on the design and development of the Canadian sys- tem and is presented and mapped in Appendix B. Table 18.3 presents the approximate equivalents of
(
(
(
b
b
)
)
Low-pH soil solution
Water table
(a)The podsolization process is typical in cool and moist climatic
regimes.
Salinization complicates farming in these drier lands. The introduction of irrigation water may either waterlog poorly drained soils or lead to salinization. Nonetheless, vegetation does grow where soils are well drained and low in salt content. Focus Study 18.1 dis- cusses the battle between salinization and waterlogging in irrigated lands in California.
Vertisolic Order Vertisolic soils occur in heavy- textured material that is high in clay content (≥ 60% clay), especially smectite, a shrinking and swelling clay. These soils have little development of horizons, and when a soil profile is exposed along a crack its sides are marked by slickensides (a smooth, polished rock sur- face) and usually occur under the layer of highest mix- ing. The shrinking and swelling of the clays resulting from wetting and drying cycles are strong enough to groove and polish surfaces along internal shear planes in the soil and prevent horizons from fully developing. However, Vertisolic soils may have an A horizon simi- lar to Chernozemic soils, or may have features similar to Gleysolic soils. Vertisolic soils occur primarily in the cool, subarid to subhumid grassland portion of the Interior Plains of western Canada (Figure 18.25) and account for just over 0.28% of the land area. This order may also occur to a more minor extent in valleys of the