Topic%201%20Soils%20notes - Topic#1 Forest Soils What is a...

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Topic #1 - Forest Soils What is a soil? A dynamic ( i.e., continuously changing) natural body composed of mineral materials, organic materials, gases, liquids and living organisms which can serve as a medium for plant growth. Soil is one of our “ultimate” resources, like water and air. Soil is a slowly renewable resource. A soil is both an ecosystem in itself & a critical part of the larger terrestrial ecosystem. How do soils form? Soil Forming Processes 1. Transformations - soil constituents are modified or destroyed, and others are synthesized. - physical and chemical weathering, formation of secondary minerals, organic matter (Oi) humus (Oa) 2. Translocation - movement of inorganic and organic materials from one horizon (up or down) to another - moved primarily by water; however, soil organisms also mix materials within and between horizons - clay, aluminum and iron oxides, humus, calcium carbonate (CaCO 3 ) and soluble salts 3. Additions - materials added to the soil profile from outside sources - organic matter from vegetation, dust (eolian) and acids from the atmosphere, salts from groundwater 4. Losses - materials removed from the soil profile - leaching of soluble constituents to groundwater or erosion of surface materials by wind or water These processes lead to horizon differentiation ( e.g., formation of soil layers with distinctive physical, chemical, biological and morphological properties). Description of Soil Horizons O horizon - a surface layer dominated by organic materials (> 20% organic carbon) Oi - slightly decomposed organic matter; can still identify the original plant and animal remains Oe - intermediately decomposed Oa - highly decomposed (can not identify the original source of the organic material) A horizon - mineral horizon (<20% organic C) which forms at the surface or beneath an O horizon - characterized by a darker color than the rest of the profile due to the accumulation of organic matter; high biological activity - layer loses materials such as iron/aluminum oxides and clays) E horizon - an intensively leached horizon in which organic matter along with iron/aluminum oxides and clay have been removed. - typically white or light gray in color due to the lack of coatings on the mineral surfaces B horizon - horizon formed beneath an A, E or O horizon and is a zone of accumulation. - may accumulate clay, iron/aluminum oxides, organic matter, carbonates, etc. C horizon - a layer of unconsolidated material showing little weathering (alteration) and biological activity ( e.g., beach sand, alluvium deposited by rivers, glacial till deposited by glaciers). R layers - consolidated rock that can not be dug with a shovel and shows little evidence of weathering ( e.g., granite, sandstone).
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What determines the kind of soil that forms? Soil Forming Equation:
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This note was uploaded on 04/22/2011 for the course PLS 144 taught by Professor Rice during the Fall '08 term at UC Davis.

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Topic%201%20Soils%20notes - Topic#1 Forest Soils What is a...

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