HPU NCS2200 Soil formation


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HPU NCS2200 Earth Science for elementary education majors summer 2104 online course soil formation lecture

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HPU NCS2200 Soil formation

  1. 1. 10.4 Soil Components • Components of soil – mineral grains (clay, silt, sand, rock fragments), organic matter, water, gas. air 25% water 25% mineral matter 45% organic matter 5%
  2. 2. Soil Profile • Horizons – soils develop a layered structure, the layers are called horizons; (from top) o O horizon – mostly litter and humus • Litter – organic debris on the ground’s surface • Humus – decomposed litter, increases water-holding capacity o A horizon – mixture of humus, sand, silt, clay • O + A = topsoil o B horizon – subsoil, low organics o C horizon – partially weathered rock o Water moves through soil and leaches ions • Water, ions, clay from “A” end up in “B”
  3. 3. Fig. 10.15a, p.241
  4. 4. Fig. 10.15b, p.241
  5. 5. Fig. 10.16, p.244
  6. 6. 10.4 Factors affecting soil development • Rates of plant growth & decay – affects humus and chemistry • Slope aspect & steepness o Aspect – the direction a slope faces • Time – chemical weathering is usually slow • Soil transport – streams and winds move sediments
  7. 7. Soil Texture • Determined by soil particles o Sand – largest o Silt – middle o Clay – smallest • Percentage of each particle within the volume give the soil type • Use the soil triangle to determine soil type
  8. 8. 1) Find Percentage Of each particle Type 2)Follow the lines for each percentage Until they intersect At a point. This give the soil Type.
  9. 9. 1) Find Percentage Of each particle Type 2)Follow the lines for each percentage Until they intersect At a point. This give the soil Type.
  10. 10. Permeability and Porosity• Permeability o The ability to transmit (or release) fluids (water) • Porosity o The volume of spaces between the soil particles Water Water High permeability Low permeability Fig. 10.17, p. 224
  11. 11. Porosity vs Permeability• The larger the particle size the larger the spaces between particles BUT there are fewer spaces o Sand has a high permeability because of large pore SIZE • Gives sand the ability to DRAIN a lot of water o Clay has a high porosity because of the NUMBER of pores • Gives clay the ability to HOLD onto a lot of water https://www.youtube.com/watch?v=39FfOa1gTX4&list=PLXKxye83Oxiy0qHna6eBa 6HMIcQZuJjph&index=6
  12. 12. SOIL EROSION AND DEGRADATION • Soil erosion is the movement of soil components, especially surface litter and topsoil, by wind or water. ►Soil erosion increases through activities such as farming, logging, construction, overgrazing, and off-road vehicles. Figure 13-9
  13. 13. Soil Degradation • Degradation – to degrade or lower the ability of the soil oMechanisms of Degradation • Erosion • Desertification • Salinization • Waterlogging
  14. 14. Soil Degradation • Erosion oMechanisms for erosion • Sliding downhill • Moving water • Wind
  15. 15. SOIL EROSION AND DEGRADATION • Soil erosion lowers soil fertility and can overload nearby bodies of water with eroded sediment. o Sheet erosion: surface water or wind peel off thin layers of soil. o Rill erosion: fast-flowing little rivulets of surface water make small channels. o Gully erosion: fast-flowing water join together to cut wider and deeper ditches or gullies.
  16. 16. Global Outlook: Soil Erosion • Soil is eroding faster than it is forming on more than one-third of the world’s cropland. Figure 13-10
  17. 17. Desertification: Degrading Drylands • About one-third of the world’s land has lost some of its productivity because of drought and human activities that reduce or degrade topsoil. Figure 13-12
  18. 18. Soil Degradation • Causes of Desertification  Overgrazing  Agricultural overuse  Deforestation  Urban development Desertification – the complete loss of topsoil Preventing the remaining soil from retaining water and nutrients creating infertile substanc Moderate Severe Very severe
  19. 19. Soil Degradation • Salinization o Increase in the salt content of the soil due to irrigation • Waterlogging o Impermeable clay layer below soil traps water innundating root systems
  20. 20. Waterlogging of Soils: A Downside of Irrigation • Example of high evaporation, poor drainage, and severe salinization. • White alkaline salts have displaced cops. Figure 13-14
  21. 21. Fig. 13-15, p. 281 CleanupPrevention Soil Salinization Solutions Reduce irrigation Switch to salt- tolerant crops (such as barley, cotton, sugarbeet) Flush soil (expensive and wastes water) Stop growing crops for 2–5 years Install underground drainage systems (expensive)
  22. 22. Case Study: Soil Erosion in the U.S. – Some Hopeful Signs • Soil erodes faster than it forms on most U.S. cropland, but since 1985, has been cut by about 40%. o 1985 Food Security Act (Farm Act): farmers receive a subsidy for taking highly erodible land out of production and replanting it with soil saving plants for 10-15 years.
  23. 23. Summary • Weathering o Two types – Mechanical & Chemical o Factors that affect rate of weathering • Erosion – movement of particles • Porosity vs Permeability • Soil Formation o Soil horizons & types • Problems with soil erosion