Canadian System of Soil Classification

Transcription

1 LAST LECTURE Soil acidity (ph) THIS LECTURE Canadian Soil Taxonomy Canadian System of Soil Classification There is a reasonable agreement between the US system and the Canadian system. Canadian has easier names. Based on Russian terminology. See pp in the text for comparison between classification systems. DIAGNOSTIC SOIL HORIZONS Based on a unit called the epipedon. Usually located in the upper-most part of the soil horizon (A and sometimes B horizons). May also include properties of the eluvial horizons. Also diagnostic subsurface horizons and soil moisture regimes (e.g. argillic, spodic, etc,, and aquic, udic, etc. see soils notes 5) EPIPEDON DIAGNOSTIC HORIZONS Brunisolic Order Relatively young soils. Weakly expressed B horizon. Found in boreal forest or in transition zones. Presence of Al and Fe give it a dark colour. Beginning of profile development Not yet at the perceived mature state. Ochric epipedon, or weakly developed Mollic or Umbric. 1

2 Brunisols Areas with adequate moisture. May be humid and sub-humid regions or cool humid regions. Presence of Fe and Al and some weatherable minerals. No illuvial horizon (silicate clay, amorphous clay, or organic carbon). Brunisolic Order Distribution and use: 9% of the world land area. Found in most climates and physiographic conditions. Prominent in the Tropics and Mountainous areas. Variable productivity Very productive in Pacific NW, not so in NY and Pennsylvania. Gleysolic Order Brunisolic/Gleysolic Order Related to Brunisols, but: Must have a gleyed or mottled subsurface horizon. Periodic or sustained reducing conditions. Can be caused by high ground water levels. Found in shallow depressions, level low-lands. No world equivalent. Canadian system modification to reflect environment. 10/22/ Gleysolic Order Chernozemic Order Grassland soils. Generally darker due to the organic matter content. A horizon 10 cm thick. Must have 1-17% organic carbon. 30% organic matter. Mollic epipedon. Granular upper horizon. 7% of total land surface area. Disproportionately high amount of food production function of geography. 2

3 Chernozems Chernozems of the Prairies. Soils that have a dark coloured surface horizon and are base rich. Nearly all have a mollic epipedon. Brown Dark Brown Chernozems of the Prairies. Dark Brown Black Figure 3.22 Chernozemic Order Cryosolic Order Permafrost within 1 m of the surface. Mineral or organic soil Can be dry or wet. Young soils with little profile development. Characterized by cold climates and frozen soil conditions for much of the year. Slows the rate of soil development. Must have a permafrost layer (below 0 C for 2 years). May also experience Cryoturbation. Produce pattern ground. 8.6 % of land area (12 million km 2 ). 3

4 Cryosolic Cryosolic Order Soils that have permafrost within 1 m of the soil surface Have frozen materials within 100 cm of the soil surface and have permafrost within 200 cm. Luvisolic Order Luvisolic Order Generally more strongly weathered. Can occur in cool or hot regions. Characterized by sub-surface diagnostic horizons with silicate clays. Eluvial Bt horizon. Usually not well structured. Fairly thick horizon. Sandy A horizon. Distribution and use. 10% of land surface area productive soils. May be more susceptible to erosion given their more moist climate and deeper weathering (sandy A-horizon). Luvisol Gray Luvisol Found in foothills and other parkland regions of Alberta. Soils that have: - an argillic, - kandic (Fe, Al, and kaolinite clay), or - natric (argillic, columnar structure, and >15% Na saturation in CEC) Horizon. - a base saturation of 35% or greater. Boreal mixed wood spruce/aspen stands on soil formed in lacustrine sediments. Developed in clay parent material on an imperfectly drained site. Diagnostic properties of Luvisolic Order - light coloured eluvial horizons and B horizons with accumulation of silicate clays. 4

5 Luvisolic Order Organic Order Must contain > 17% organic carbon. Must have organic accumulation > 15 cm. Depending on class 40 to 60 cm. Organic Order Organic/Histosols Organic soils without permafrost. Little profile development because of anaerobic environment Lack of Oxygen. Organic matter accumulation in Bogs and Fens Bogs are acidic (granitic), Fens are Alkaline (limestone). Dominantly organic. Organic Order Very important natural wetland environments Covers about 1% of land surface area Can be productive, but need draining and treatment for ph Often too expensive Mined for peat Organic matter for gardens Fuel 5

6 Podzolic Order Coarse to medium texture. Acidic parent material. Formed under forested conditions (acidic litter). Coarse-textured parent materials. Occur in moist to wet environments. Subsurface accumulation of Al or Fe oxides. Have a light ash-coloured eluvial horizon. Have a black or red illuvial horizon. Podzol Soils in which amorphous mixtures of organic matter and aluminum, with or without iron, have accumulated. Can have multiple podzols stacked Podzolic Order Podzolic Order Distribution and use. 3% of land area. Not naturally fertile. Require fertilization. Sandy texture works well for vegetable production. Doesn t work for fertilizers and pesticides. Get into the water table. Regosolic Order Young parent material. No real development of a B horizon. Weakly developed mineral soils without genetic subsurface horizons. Most have an Ochric epipedon. Broad range of soil productivity. Very high on recently deposited volcanic material, low on recently deposited rock. Regosol Soils that have little or no evidence of development of pedogenic horizons. Often Sandy. 6

7 Regosolic Order Regosolic Order Regosols may have nothing in common. Some soils will only be part of this order for a while. Distribution and use: Found on 16% of the total land surface area. New areas like mountain areas, deserts, volcanic zones. Could be very productive or not. Solonetzic Order Solonetz Same as Chernozems and Luvisols with a Natric horizon. Strongly structured B horizons. Prismatic or columnar structure. Not a permanent state. Clay concentration decreases. Hydraulic conductivity increases. Structure of B horizon breaks down. The Forgotten Soils in the Canadian System. We don t have these environments in Canada. Let s think about it? Tropics. Deserts. Volcanic Ash. Old land surfaces. Odd clay types. Look at the American system for these. Vertisols Has shrinking and swelling clays. Up to 6% clay. May have chernozemic A-horizon. Must have periods of drying and wetting. Can have gleying due to saturated conditions. Cracking can occur to a depth of 1 m. Dark in colour (not from OM, but from dark minerals). 7

8 Vertisols Vertisols Swelling clays. Lack OM Found in humid and semi-humid regions. Often regions of native grasslands. Distribution and Use: 2.5% of the total land area. Problematic for building. Not great for agriculture, as the clays are sticky. Andisols Andisols (volcanic ash soils). Formed in volcanic ash and dust from recent geological times. Have not had sufficient time to become highly weathered. Many have Melanic epipedons. Organic matter accumulation is rapid due to development of clay complexes. 10/22/ Andisols Weakly weathered soils with much volcanic glass as well as more strongly weathered soils. Andisols Unique set of parent material conditions. Limited distribution. Distribution and use: Less than 1% of the land area. Generally very productive soils. 8

9 Aridisols Second largest global coverage (12%) Characteristic water deficiency. Ochric epipedon. May have concentrations of soluble minerals (salt, gypsum, calcium carbonate), due to lack of moisture. Aridisols Characterised by the moisture regime (lack of moisture). Aridisols Distribution and use. Only moist for short periods of time each year. Generally not terribly productive without irrigation. Ultisols Ultisols Formed by clay mineral weathering and translocation of clay. Leaching of base cations from the profile. Formed on old land surfaces. Usually under forested conditions Have and ochric or umbric epipedon. 9

10 Ultisols Ultisols have a horizon that contains an appreciable amount of translocated silicate clay Ultisols Relatively acidic B-horizons Low base saturation of clays. Distribution and use. 9% of land surface area. Not great for agriculture in native state. Respond well to management Require fertilizer and lime. Oxisols Oxisols. Most highly weathered soils. Form in moist hot climates (tropics). Equatorial regions. High clay content, but low base activity. Can be worked when dry. Often RED. Oxisols Weathered red soils of the tropical and subtropical regions. Oxisols Distribution and use: 8% of world soil areas Not glaciated or eroded. Not well known due to location. Best left under forested environments. Nutrient cycling in trees. 10

11 READING FOR TUESDAY REVIEW LECTURE FOR MID-TERM All chapters and lecture notes for the mid-term Prepare some questions on material that you don t quite understand 11