Chapter 7 section 3 (soil erosion)


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Chapter 7 section 3 (soil erosion)

  1. 1. Soil Erosion<br />Chapter 7 Section 3<br />
  2. 2. I. Soil: An Important Resource<br />Erosion<br />The process of carrying away sediment from one place to another. <br />Soil Erosion is harmful because plants do not grow well when topsoil has been removed. <br />
  3. 3. II. Causes and Effects of Soil Erosion<br />Water or Wind Erosion<br />Erosion occurs as water flows over Earth’s surface or when wind picks up and transports sediments. <br />Erosion is generally more severe on steep slopes than on gentle slopes. <br />Erosion is more severe in areas where there is little vegetation. <br />
  4. 4. II. Causes and Effects of Soil Erosion<br />A. Water or Wind Erosion<br />Trees protect the soil from erosion; when forest is removed, soil erodes rapidly.<br />Under normal conditions soil erosion occurs at the same rate as soil production. <br />Humans sometimes cause erosion to occur faster than new soil can form. <br />When people remove ground cover erosion increases. <br />
  5. 5. B. Agriculture Cultivation<br />Topsoil contains many nutrients, holds water, and has a porous structure that is good for plant growth. <br />If topsoil erodes rapidly, the nutrient balance might be negative. <br />Fertilizer may be needed to compensate for nutrient loss. <br />The remaining soil might not have the same open structure and water holding ability that topsoil does. <br />Plowing is the mechanical turning and loosening of the soil. <br />Plowing increases the rate of erosion because the soil can now be moved more easily. <br />
  6. 6. C. Forest Harvesting<br />When forests are removed, soil is exposed and erosion increases. <br />Creates problems, especially in tropical regions. <br />Soils in tropical rain forests appear rich in nutrients but are almost infertile below the first few centimeters. <br />Soil is only useful to farmers for a few years. <br />Farmers/lumber jacks then clear new land, repeating the process and increasing the damage to the soil. <br />
  7. 7. D. Overgrazing<br />Increases soil erosion.<br />In some arid regions of the world, sheep and cattle raised for food are grazed on grasses until almost no ground cover remains to protect the soil. <br />In these regions plants grow back slowly because they receive little rain. <br />Without protection the soil is carried away by wind, and the moisture in the soil evaporates. <br />
  8. 8. E. Excess Sediment<br />If soil erosion is severe, sediment can damage the environment. <br />Severe erosion occurs where land is exposed. <br />Examples: <br />Strip Mined Areas<br />Construction Sites<br />Eroded soil is moved to a new location where it is deposited. <br />If the sediment is deposited in a stream the stream channel might fill<br />
  9. 9. III. Preventing Soil Erosion<br />Manage Crops<br />Farmers work to slow soil erosion. <br />Plant shelter belts of trees to break the force of the wind. <br />Plant crops to cover the ground after the main harvest. <br />In dry areas instead of plowing under crops, many farmers graze animals on the vegetation.<br />
  10. 10. A. Manage Crops<br />No-Till Farming<br />Usually famers till or plow their fields one or more times each year. <br />Using no-till farming farmers leave plant stalks in the field over the winter months. <br />Seed crops without destroying stalks and without plowing the soil. <br />Provides year-round cover for the soil, which reduces water runoff and soil erosion. <br />
  11. 11. A. Manage Crops<br />Chisel Plowing<br />Instead of turning over a complete field, chisel plows cut small furrows between previously planted and harvested crops<br />Previous crop roots hold soil, decaying plants fertilize the soil<br />Newly loosened area is planted<br />
  12. 12. A. Manage Crops<br />Cover Cropping<br />Farmers plant two crops that can grow together, harvest one & leave the other to continue growing<br />Ex: Grains with Grasses<br />Grains get combined off in early summer,<br />Grasses continue to grow and can be cut as hay<br />
  13. 13. B. Reduce Erosion on Slopes<br />On gentle slopes, planting along the natural contours of the land, called contour farming, reduces soil erosion. <br />This practice slows the flow of water down slopes and helps prevent the formation of gullies. <br />
  14. 14. B. Reduce Erosion on Slopes<br />Where slopes are steep, terracing often is used. <br />Terracing is a method in which steep sided, level topped areas are built onto the sides of steep hills and mountains so that cops can be grown. <br />These terraces reduce runoff by creating flat areas and shorter sections of slope. <br />Terracing has been used in the Philippines, Japan, China, and Peru for centuries. <br />
  15. 15. C. Reduce Erosion of Exposed Soil<br />Variety of methods used to control erosion of exposed soil. <br />During construction water is sometimes sprayed onto bare soil to prevent erosion by wind. <br />When construction is complete topsoil is added and trees are planted. <br />At strip mines, water flow can be controlled so that most of the eroded soil is kept from leaving the mine. <br />After mining is complete the land is reclaimed . <br />This means that steep slopes are flattened and vegetation is planted. <br />