NRES 201 Lecture 6 Outline of Last Lecture I The Pleistocene Ice Age II Parent materials a Glacial drif b Eolian deposits III Climate Outline of Current Lecture IV Organisms V Topography VI Time VII Weathering Current Lecture Organisms o Plants have a huge role in forming soil o Vegetation Plant growth generates organic matter Photosynthesis fixes atmospheric CO2 Organic C deposition in roots and residues Supplies energy for microbes that o Decompose organic substrates o Contribute to humus formation o Bring about many chemical changes o Promote aggregation Plant roots alter the parent material by o Attacking minerals o Generating acidity o Mobilizing nutrients o Stimulating microbial activity Plant shoots initiate surface stratification by o Litter deposition o Nutrient enrichment o Building granular structure o Enhancing water infiltration The natural vegetation affects what type of soil forms o Higher organic matter content under grass than forest These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute o o o o Grasses deposit all of their fixed C in the soil Trees store most of their C in wood A drier climate for grass reduces leaching losses Greater soil acidity under coniferous than deciduous trees Animals o Burrowing animals can have a positive or negative effect on soil formation o Positive effects Increased exposure of subsurface material and surface weathering Greater air and water movement Digestive activities of earthworms improve structure and enhance nutrient cycling o Negative effects Mixing impedes horizontal development Increased erosion hazard Human activities have important effects on soil formation o Negative Soil has no legal protection Burning natural vegetation Tillage or construction activities Irrigation o Positive Roofop gardens Topography Defined as landscape position as characterized by elevation slope and direction and angle Elevation affects precipitation temperature and vegetation Time Soil formation is a very gradual process Young differentiated from mature soils on the basis of profile development not chronological age Weathering o Physical process Rocks are reduced in size and do not undergo any chemical changes Disintegrated by temperature Differential expansion When heated by sunlight or fire some minerals expand more than others This creates stresses that eventually fracture the rock o Chemical processes Primary minerals decomposed and new minerals formed Chemical binding of intact water molecules to minerals Increases mineral size and decreases mineral stability Hydrolysis Most important chemical weathering process Involves dissociation of water and mineral decomposition by ion replacement Dissolution Due to its polar nature water is an excellent solvent for ionic solids such as minerals Acidic Dissolution Acidity enhances mineral solubility
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