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Notes - 1/25/08 SOIL ENVIRONMENT -What defines a soil?...

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SOIL ENVIRONMENT -What defines a soil? “the naturally occurring, unconsolidated mineral and organic material at the earth’s surface that provides an environment for living organisms” weathered layer of the earth’s crust plant roots mineral and organ Recently referred to as the earth’s critical zone Role in controlling the earth’s environment and thus in affecting the sustainability of life on the planet -Soil as an environmental interface Exchange of matter and energy. Interface between the biosphere, the hydrosphere, the atmosphere and the lithosphere. Air, biota organic, minerals, water is what soil is composed. Water will interact with hydrosphere, biota organic with biosphere, air with atmosphere, and minerals with lithosphere. Litho Greek for rock. -Submerged soils Soils may also be covered with water to a depth of up to 0.5 m as in coastal tidal marshes or inland water areas -Soil forming factors Biota, time, parent material, climate, topography -Soil profile Vertical cut in soil. O,A,E,B,C, Different layers are called horizons. Soil consist of O,A,E,B and parent material is C horizon -Soil components Solids are spatially arranged in a very complex way, forming tortuous pore spaces. Porosity 30-60% Soil organic mater composition-Humic substances 50%, living biomass 4, nonhumic substances 30, macroorganic matter 16 Soil biomass composition- Macrofauna22, microorganisms 70, roots 8 Bacteria important in numbers fungi in biomass -Porous medium-Solid phase, liquid phase (soil solution) Gaseous phase(soil atmosphere) Unsaturated zone=vadose zone. Water and air occupy pores Saturated zone water fills all pores. Groundwater table in between zones. Interfaces-Solid/liquid, liquid/gas, gas/solid Soil properties- texture, structure. -Soil textures Particles >2mm are not considered as soil materials Texture-relative percentage of sand silt, and clay Sand:50-2μm in diameter. More larger pores so less water retention Silt:2-50μm Clay: smaller than 2μm. Smaller pores so more water retention. Primary silicate mineral- minerals that are identical to what is in the parental material Secondary silicate mineral- chemically changed with time. Quartz consist of feldspar and mica Sand-primary minerals, feels gritty, low specific area, not cohesive Specific surface area- related to volume. The smaller the object the larger the specific surface area of the object. Clay-secondary minerals, swells/shrink, negatively charged, plastic behavior, feels sticky when wet, very high specific area. Charge will repel anions and attract cations. Silt-primary minerals, feels like flour, medium specific area, retain water beter than sand but drain better than clay. -Textural triangle- refer to picture Loamy soils are the best conditions for agricultural purposes -Soil density Particle density Ps: weight of solid particles/volume of solid particles (usually considered as 2.65 g cm^-3; Quartz) Dry bulk density Pd: dry weigh of soil/volume of the soil Organic soil pd~0.8
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Notes - 1/25/08 SOIL ENVIRONMENT -What defines a soil?...

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