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Chapter 7 section 3 (soil erosion)

Chapter 7 section 3 (soil erosion)






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    Chapter 7 section 3 (soil erosion) Chapter 7 section 3 (soil erosion) Presentation Transcript

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