APES 4.2 Soil Formation and Erosion

Soil Formation

  • Soil is formed when parent material is weathered, transported, and deposited
  • Parent material is the original rocks that were broken down to form the base of the soil
  • Weathering is the mechanical breakdown of rock

Factors

  • There are several factors that go into and influence soil formation
  • The type of parent material
    • Rocks are broken down by wind and rain
    • Soil tends to retain basic chemistry of these rocks
  • Climate
    • Average temperature and moisture change rate of weathering and leaching (nutrients leaking into water)
    • Wind redistribution as well
  • Topography
    • Slope of the land may affect erosion
  • Biological factors
    • Plants, animals, microorganisms
  • Time
    • Soil formation is continuous, there’s no end

Soil Profile/Horizon

  • Over time, soil layers build up and form common layers
  • These are known as a soil horizon or profile
  • On top is the organic matter, such as grasses, shrubs, trees, and more
  • Under that is the surface horizon
  • The next layer is the subsoil
  • The last layer is the substrata
  • Below this is the bedrock

Soil Erosion

  • Over time, soil erodes due to several factors
    • Water
    • Wind
    • Gravity
    • Human factors
    • These often lead to water contamination

Human Factors

  • The way humans farm influences soil erosion
  • The first problem is deforestation
    • The lack of roots holding down soil leads to soil being washed or blown away easily
    • For agriculture, trees are often replaced with plants that make the erosion worse, like soybean and wheat
  • The second problem is overgrazing
    • Pastureland can lead to cattle overeating and the top layer of soil then erodes with wind and rain
  • The third is pesticides and fertilizers
    • These can change the chemistry of coil, killing important microorganisms
  • The fourth is tillage practices
    • Turning and breaking up soil keeps the top layer from accumulating organic material and roots

Erosion from Water and Solutions

  • Sheet erosion occurs when the surface layer of soil is removed by water
    • This can be avoided by maintaining plant cover
  • Rill erosion is when small channels of water erode the soil and start create larger and larger rivulets
    • Strip cropping or contour plowing can mitigate this
  • Gully erosion is what happens after rill erosion when the little channels widen
    • Diverting water away from the rills and gullies is the best solution