weathering soils

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Information about weathering soils

Published on January 22, 2008

Author: Carolina


CONCEPT OF THE WEATHERING PROFILE:  CONCEPT OF THE WEATHERING PROFILE Weathering Zone: Zone of Alteration Differing Physically, Chemically, or Mineralogically from Adjacent Zones, and Extending Laterally Beneath the Land Surface. Weathering Profile: Vertical Assemblage of Weathering Zones from the Land Surface to and Into the Unweathered Parent Material. CONCEPT OF WEATHERING PROFILE:  CONCEPT OF WEATHERING PROFILE Includes Not just the Soil, but any Near-surface Material Affected by Weathering. For Upper Midcontinent of North America: Parent Material is Originally Calcareous (Glacial, Eolian, Etc.) MIDCONTINENT WEATHERING PROFILE:  MIDCONTINENT WEATHERING PROFILE I Eluviated, organic, deeply weathered, leached of carbonates, oxidized II Illuviated, inorganic, deeply weathered, leached of carbonates, oxidized III Not strongly weathered, leached, oxidized IV Not strongly weathered, unleached, oxidized V Unaltered parent material, unleached, unoxidized THE SOIL PROFILE:  THE SOIL PROFILE Soil Profile: “Layered” Upper Part of the Weathering Profile Resulting from Alteration of Parent Material by Primarily Biochemical Processes. “Layers” Better Known as Soil Horizons. Soil Profile Coincides with Zones I and II and the Upper Part of Zone III of the Weathering Profile. THE SOIL PROFILE:  THE SOIL PROFILE Criteria for Distinguishing Major Soil Horizons Organic Content [Amount and Type of Veg.; Preserv’n] Chelation Water Absorption Carbonic Acid Color Soil Texture Soil Structure SOIL HORIZONS:  SOIL HORIZONS O: Large Amounts Organic Matter A: Humus And Mineral Matter E: Low In Clay, Sesquioxides B: Accumulation Of Clay, Sesquioxides C: Slightly Weathering Parent Material D: Unweathered Parent Material R: Bedrock TYPES OF A HORIZONS:  TYPES OF A HORIZONS MOLLIC: Dark, > 1% Organics, > 50% Base Saturation Usually Developed Under Grass. UMBRIC: Dark, > 1% Organics, < 50% Base Saturation Usually Developed Under Forest. OCHRIC: Light, < 1% Organics Usually Developed Under Semiarid Vegetation. TYPES OF B HORIZONS:  TYPES OF B HORIZONS ARGILLIC: High in Clay (Textural B) NATRIC: High in Exchangeable Sodium SPODIC: High in Organics and Sesquioxides OXIC: High in 1:1 Clays, Hydrated Oxides of Fe and Al CAMBIC: Oxidized to Red (Color B) FACTORS OF SOIL FORMATION S or s = f (cl,o,r,p,t…..):  FACTORS OF SOIL FORMATION S or s = f (cl,o,r,p,t…..) S = the soil; s = any soil property cl = climate: precipitation and temperature o = biota; vegetation usually predominant r = topography; position on a slope; affects soil drainage, soil erosion; slope aspect also p = parent material t = time; duration independent factors?? SOIL CLASSIFICATION LOWER LEVELS:  SOIL CLASSIFICATION LOWER LEVELS Soil Series: Soils with Similar Profiles because of Same or very Similar Parent Materials. Example: Miami Series (P.M. Wisconsinan Till) Soil Type: Subdivision of Series Based on Range of Textures. Examples: Miami Silt Loam, Miami Sandy Clay, Miami Clay Loam SOIL CLASSIFICATION HIGHER LEVELS:  SOIL CLASSIFICATION HIGHER LEVELS 11 Orders Distinguished by Diagnostic Horizons Suborders Named for Diagnostic Physical or Chemical Property Prefix: that Property Suffix: Reflects Order Great Groups and Subgroups: More Detailed Properties SOIL CLASSIFICATION AN EXAMPLE: Humodic cryudent:  SOIL CLASSIFICATION AN EXAMPLE: Humodic cryudent ent = entisol (order) a soil with a weakly-developed, A-C profile, little or no clay accumulation ud = udic (suborder) moist and has low to moderate organics SOIL CLASSIFICATION RELEVANT TABLES IN TEXT:  SOIL CLASSIFICATION RELEVANT TABLES IN TEXT T3.8/69 Formative Elements of Orders of USDA System T3.7/68 Orders and Suborders T3.9/70 Naming Suborders T3.10/70 Naming Great Soil Groups Also Useful: 3.13/69 SOIL CLASSIFICATION AN EXAMPLE:  SOIL CLASSIFICATION AN EXAMPLE cry = cold (great group) odic = sodic B horizon + Hum = weakly developed (subgroup) Try one yourself. CLIMATE AND VEGETATION AS SOIL-FORMING FACTORS:  CLIMATE AND VEGETATION AS SOIL-FORMING FACTORS Podzolization Humid, Temperate Climates Forest Vegetation Acidic Conditions Removal of Bases Translocation of Fe, Al (Primarily By Chelation) Creation of E Horizon SOIL-FORMING FACTORS:  SOIL-FORMING FACTORS Podzolization North: Spodosols, Alfisols Colder, More Organic Matter South: Ultisols Warmer, Less Organic Matter, More Oxidation SOIL-FORMING FACTORS:  SOIL-FORMING FACTORS Laterization Tropical Conditions Organics Oxidized Silica Leached 1:1 Clays or Hydrated Al Oxides and Hydroxides Oxisols SOIL-FORMING FACTORS:  SOIL-FORMING FACTORS Calcification Dry Cimates Calcium Carbonate Accumulation, Depth Related To Precipitation Subhumid to Semiarid: Mollisols Arid: Aridisols PALEOSOLS:  PALEOSOLS Soils that Formed on a Past Landscape Types: Buried Welded: Ground Soil Merged with it Exhumed Relic PALEOSOLS:  PALEOSOLS Importance Influence on Ground Soil Development Stratigraphic Correlation Reconstruction of Paleoclimate, Vegetation

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