Page 624 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

588 part IV Soils, Ecosystems, and Biomes
POTET equal to or greater than PRECIP
accumulates in the upper soil layers and mottling occurs in the lower layers resulting from reduction of iron and other elements. The Gleysolic order of soils is defined on the basis of colour and mottling that results from chronic reducing conditions inherent in poorly drained mineral soils under wet conditions. A high water table and long periods of water saturation are common to these soils. Gleysolic soils are spotty in areal distribution, appearing within other soil orders, occasionally being the dominant soil of an area (Figure 18.17, page 592), and account for 3% of the land surface. A diagnostic Bg horizon is present in these soils that are rated as high to medium in fertility. The great groups of this order are Luvic Gleysol, Humic Gleysol, and Gleysol. There are 13 subgroups.
luvisolic Order Eluviation-illuviation processes pro- duce a light-coloured Ae horizon and a diagnostic Bt horizon. Soils of this order develop beneath the mixed deciduous–coniferous forests. There are major occur- rences of Luvisolic soils in the St. Lawrence Lowlands. Luvisolic soils occur from the zone of permafrost to the southern extremity of Ontario and from Newfoundland to British Columbia. The greatest areal extent is in the north- ern Interior Plains under deciduous, mixed, and conif- erous forest (Figure 18.18, page 593). The fertility rating is high for these soils that cover 7% of the land surface. The great groups of the Luvisolic order are Grey Brown Luvisol and Grey Luvisol and include 18 subgroups.
Organic Order Soils of the Organic order are composed largely of organic materials. These include peat, bog, and muck soils and are commonly saturated with water for prolonged periods of time (Figure 18.19, page 594). Organic soils are widespread and are associated with poorly to very poorly drained depressions, but can be found under upland forest environments (Folisols) and account for 9% of the land surface. To qualify as organic, these soils must contain greater than 17% organic carbon and exceed 30% organic matter by weight overall. Organic soils are rated as high to medium in fertility depending upon drainage and the available nutrients. The great groups contained in this order are Fibrisol, Mesisol, Humisol, and Folisol and include 31 subgroups.
Podzolic Order Podzolic soils develop beneath conif- erous forests and sometimes heath vegetation and result from leaching of the overlying horizons in moist, cool to cold climates (Figure 18.20, page 595). These soils result from podsolization, a soil-forming process in which a highly leached soil with strong surface acidity devel- ops in cool, moist climates (Figure 18.21, page 596). The Boreal forest that encircles the globe in northern latitudes is largely underlain by Podzolic soils. Iron, aluminum, and organic matter form the L, F, and H horizons and are redeposited in the Podzolic B horizon. A diagnostic Bh, Bhf, or Bf horizon is present depending upon the great group. Podzolic soils dominate in western British Colum- bia, Ontario, Québec, and Atlantic Canada and account
Dark colour, high in bases
Calcic horizon; possible formation of caliche
O A
E
B
C
Dense sod cover of interlaced grasses and roots
Accumulation of excess calcium carbonate
▲Figure 18.13 Calcification in soil. The calcification process in drier Brunisolic soils (in the the United States: Aridisol/Mollisol soils) occurs in climatic regimes that have potential evapotranspiration equal to or greater than precipitation.
problems associated with salinization and the buildup of toxic materials in the soil. The great groups of the Chernozemic order are Brown Chernozem, Dark Brown Chernozem, Black Chernozem, and Dark Grey Cher- nozem. Within this order are 38 subgroups. Figure 18.15 shows the transition between great groups within the Chernozem order, principally in response to climate differences.
Cryosolic Order The Cryosolic order dominates the northern third of Canada, with permafrost closer to the surface and composed of mineral and organic soil deposits. Generally, Cryosolic soils are found north of the treeline, in fine-textured soils in the subarctic forest, or in some organic soils in Boreal forests (Figure 18.16, page 591). The Ah horizon is lacking or thin. Cryoturbation (frost action) is common and is often denoted by patterned ground cir- cles, polygons, and stripes. Cryosols have a mean annual temperature less than or equal to 0°C. The subgroups of this order are based on the degree of cryoturbation and the nature of the mineral or organic soil material. Fertil- ity ratings are not applicable to these soils that cover 28% of Canada’s land area. The great groups are Turbic Cryo- sol, Static Cryosol, and Organic Cryosol, and there are 15 subgroups in this order.
gleysolic Order Gleysation is a soil-forming pro- cess in poorly drained conditions where organic matter