NRES 201 Lecture 6 Outline of Last Lecture I. The Pleistocene Ice AgeII. Parent materialsa. Glacial drifb. Eolian deposits III. Climate Outline of Current Lecture IV. OrganismsV. TopographyVI. TimeVII. Weathering Current Lecture- Organismso Plants have a huge role in forming soilo 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 formationo Bring about many chemical changeso Promote aggregation- Plant roots alter the parent material by:o Attacking mineralso Generating acidityo Mobilizing nutrientso Stimulating microbial activity - Plant shoots initiate surface stratification by:o Litter depositiono Nutrient enrichmento Building granular structureo Enhancing water infiltration - The natural vegetation affects what type of soil formso Higher organic matter content under grass than forestThese 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 Grasses deposit all of their fixed C in the soilo Trees store most of their C in woodo A drier climate for grass reduces leaching losses. o Greater soil acidity under coniferous than deciduous trees. - Animalso 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 Irrigationo 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. - Weatheringo 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 thanothers. 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 ionicsolids such as minerals. Acidic Dissolution - Acidity enhances mineral
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