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Chapter 6 Section 2 Notes

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Chapter 6 Section 2 Notes

  1. 1. The Nature of Soil<br />Chapter 6: Section 2<br />
  2. 2. I. Formation of Soil<br />Weathering gradually breaks rock into smaller and smaller fragments. <br />Does not become high quality soil until plants and animals live on them. <br />Plants and animals add organic matter to the rock fragment. <br />Remains of plants and animals including leaves, twigs, roots and dead worms and insects. <br />Soil is a mixture of weathered rock , decayed organic matter, mineral fragments, water, and air. <br />
  3. 3. II. Five Factors of Soil Formation<br />
  4. 4. III. Factors of Soil Formation<br />Comparing the Factors<br />Discussion Points<br />Tropical vs. Polar<br />Steep vs. Flat<br />Limestone vs. Coal<br />Trees vs. Desert<br />New Soil vs. Old <br />
  5. 5. C. Visualization of Soil Formation<br />It may take thousands of years to form but soil is constantly evolving from solid rock. <br />
  6. 6. IV. Visualization of Soil Formation<br />Soil enters the cracks providing some nutrients for plants, weeds, etc. to grow.<br />
  7. 7. IV. Visualization of Soil Formation<br />These organisms provide nutrients, mechanical, and chemical weathering.<br />
  8. 8. IVVisualization of Soil Formation<br />Over time the soil becomes more fertile and allows more growth; which reduces the erosion rate. <br />
  9. 9. V. Composition of Soil<br />Most organic matter in soil comes from plants. <br />Leaves, stems, and roots all contribute organic matter to soil.<br />Animals and microorganisms provide additional organic matter when they die. <br />After plant and animal material gets into soil, fungi and bacteria cause it to decay. <br />The decayed organic matter turns into a dark-colored material called HUMUS. <br />Animals and insects mix the humus with the fragments of rock. <br />Good quality surface soil has approximately equal amounts of humus and weathered rock material. <br />
  10. 10. V. Composition of Soil<br />Water Filtration<br />Soil has many small spaces between individual soil particles that are filled with water or air. <br />When soil is moist, spaces hold water needed for plants. <br />During a drought, the spaces are almost entirely filled with air. <br />When water soaks into the ground, it infiltrates the pores.<br />Infiltration rate is determined by calculating the time it takes for water sitting on soil to drop a fixed distance. <br />
  11. 11. VI. Soil Profile <br />Horizons<br />Different layers of soil are called horizons. <br />All the horizons of a soil form a SOIL PROFILE. <br />Most soils have three horizons-labeled A, B, and C. <br />Most plant roots grow in the top layer of soil. <br />
  12. 12. VI. Soil Profile <br />The A Horizon<br />Top layer of soil; in a forest may be covered with litter. <br />LITTER consists of leaves, twigs, and other organic matter that can be changed to humus by decomposing organisms. <br />Litter helps prevent erosion and evaporation. <br />A Horizon is known as topsoil. <br />Generally dark and fertile and has more humus than the other horizons.<br />Dark color is caused by the humus, which provides nutrients for plant growth. <br />
  13. 13. VI. Soil Profile <br />The A Horizon<br />Since dark color absorbs solar energy more readily, soil color can greatly affect soil temperature. <br />Darker color may also indicate a higher content of soil moisture, which is important in determining seed germination for plants and the vitality of decomposing organisms. <br />
  14. 14. VI. Soil Profile <br />The B Horizon<br />Also known as subsoil. <br />Less organic matter is added so it is lighter in color than the A Horizon. <br />Less fertile than A Horizon. <br />Contains material moved down from the A Horizon by the process of LEACHING.<br />
  15. 15. VI. Soil Profile <br />The B Horizon<br />Leaching is the removal of minerals that have been dissolved in water. <br />Resembles making coffee in a drip coffeemaker. <br />Water seeps through the A Horizon and reacts with humus and carbon dioxide to form acid. <br />The acid dissolves some of the of the minerals in the A Horizon and carries the material into the B Horizon. <br />
  16. 16. VI. Soil Profile <br />The C Horizon<br /> Bottom horizon; consists of partially weathered rock. <br />Does not contain much organic matter and is not strongly affected by leaching. <br />Composed of coarser sediment than the above soil horizons.<br />Bottom of C Horizon is the rock that gave rise to the soil horizons above it. <br />Called the parent material of soil. <br />C Horizon is the soil layer that is most like the parent material. <br />
  17. 17. VII. Soil Structure<br />Four Classes of Soil Structure <br />Affect pore space and will affect a plants ability to penetrate roots. <br />Natural clumps of soil are called peds. <br />Granular<br />Granular structures are common in surface soils with high organic content that glues minerals together. <br />Earthworms, frost, and rodents mix the soil, keeping the peds small, which provides good porosity and movement of air and water. <br />
  18. 18. VII. Soil Structure<br />Platy Structures<br />Often found in subsurface soils that have been leached or compacted by animals or machinery. <br />Blocky Structures<br />Common in sub-soils or surface soils with high clay content which shrinks and swells, producing cracks. <br />
  19. 19. VII. Soil Structure<br />Prismatic Structures<br />Found in B Horizons<br />Dense and difficult for plant roots to penetrate.<br />Vertical cracks result from freezing and thawing, wetting and drying, and downward movement of water and roots. <br />Soil Consistency<br />Ability of peds and soil particles to stick together and hold their shapes. <br />
  20. 20. Section 2 Mini Lab (15 minutes)<br />
  21. 21. Section 2 Mini Lab (15 minutes)<br />Use the information on the previous slide to answer the questions below. <br />Calculate the percentage of sand in the sample. <br />Convert the percentage sand to degrees. <br />Calculate the percentage of silt in the sample. <br />Convert the percentage of silt to degrees. <br />Convert the percentage of clay to degrees. <br />
  22. 22. VIII. Soil Types<br />Soil types vary in color, depth, texture, fertility, pH, temperature, and moisture content. <br />Soil Types and Climate<br />Soil temperature and moisture content affect the quality of soils. <br />Desert soil contains little organic material and are also thinner than soils in wetter climates. <br />Prairie soils have thick, dark A Horizons because the grasses that grow there contribute lots of organic matter.<br />Temperate forest soils have less organic matter and thinner A Horizons than prairie soils. <br />Other regions such as tundra and tropical areas also have distinct soil. <br />
  23. 23. VIII. Soil Types of the United States<br />
  24. 24. IX. Other Factors for Soil<br />Parent Rock<br />Affects vegetation that grows. <br />Affects how soil is weathered. <br />Soil pH<br />Controls many chemical and biological activities that take place in soil. <br />Activities of organisms, acid rain, or land management practices could affect soil quality. <br />Time<br />If weathering has only been occurring for a short time the parent rock dominates the landscape. <br />Slope<br />On steep slopes, soils are often poorly developed. <br />In bottomlands, sediment and water are plentiful; and are often dark, thick, and full of organic material. <br />
  25. 25. IX. Other Factors for Soil<br />The slope of the land affects soil development. Thin, poorly developed soils form on steep slopes, but valleys often have thick, well developed soils. <br />Why does this happen?<br />

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