Chapter 6 Soil Environmental Factors of Soil Formation
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Soil Chapter 6 Soils, Weathering, and Erosion Environmental Factors of Soil Formation Climate Organic Activity Topographic Relief & aspect Parent Material Time Soil forms from the weathering of regolith The thin layer of weathered bedrock and organic material that supports plant life—but we also call “dirt” or detritus “soil” Weathering Physical and chemical breakdown of bedrock and regolith Physical weathering caused by temperature changes and disruption by plants and animals Chemical weathering include solution, oxydation, hydration, and hydrolysis Rate of Weathering Modes of Physical Weathering Water freezes (9% expansion) Salt crystals form (expansion) Insolation (heating of the sun) Unloading Root wedging Depends on mineral composition of regolith, surface area, and climate Smaller particles weather faster than large masses Iron-rich minerals weather faster than quartz or feldspar 1 Features and Landforms Spheroidal Weathering Exfoliation Domes Residual Soil Developed in place on underlying rock Also known as saprolite Oxisols Laterites Soil Classification Soil Profile Distinguishable layers, or horizons in mature soils Organic-rich O horizon A horizon zone of leaching B horizon zone of accumulation C horizon of weathered parent material Climate influences thickness of horizons and the rate of soil formation Transported Soil Developed on regolith and deposited by wind, glaciers, rivers, or volcanic action Loess Soil Type Distribution Classification of soil into 11 orders by their physical characteristics that reflect soil age and climate 2 Sheet and Rill Erosion Soil Problems-Erosion A major problem because soil determines earth’s carrying capacity Irreparable soil degradation has impacted an area the size of China and India combined U.S. soil losses vary greatly with location Wind Erosion Wind erodes soil on marginal land that was once cultivated and then dried out Dust bowl conditions can develop Expansive Soils Some clay minerals absorb water and expand, exerting high pressure that can crack or destroy structures Sheet erosion by running water removes a thin layer of soil Rill erosion-defined streamlets carved in the soil Mitigation Good agricultural practices Terracing Strip Cropping Crop Rotation Cover Crops Permafrost Permanently frozen ground underlying seasonally thawed soil Climate change is causing melting of permafrost in many regions 3 Settlement Settlement occurs when the applied load is greater than the bearing strength of the soil Other Soil Problems Salinization Contamination 4
