Ch16: Soil

• Soil composition:

  • Mineral matter
  • Air
  • Water
  • Humus
  • Living organisms
• Soil Profile:

  • O-Horizon - the topmost layer of soil that holds plant litter, which provides the humus for soil.
  • A-Horizon - the upper layer of soil, known as the topsoil. The home to most of the living organisms and humus of the soil, making this area darker than the rest of the soil.
  • B-Horizon - the subsoil, lighter than the rest of the soil due to less humus. Has a lot more stones due to the bedrock below it.
  • C-Horizon - the bedrock or parent material of the soil, consisting of solid rock.
• Factors influencing soil formation:

  • Time - it takes 400 years to form 1 centimetre of soil
  • Vegetation - areas with deciduous trees contain more plant litter, making the soil more fertile. Areas with coniferous trees have less plant litter, making the soil more acidic and less fertile.
  • Landscape / relief - soil in upland areas are thin due to mass movement, meaning that the soil will be poorly drained and infertile. Soil in lowland areas are thick and deep, well drained and are usually fertile.
• Brown Earth Soil:

  • The most common soil type in Ireland, found in lowland areas
  • Developed on the boulder clay that was deposited from the last Ice Age
  • Contain an even amount of sand, silt and clay
  • Deciduous forests develop on this soil, and the plant litter from the trees make the soil more fertile
• Influence of soil on vegetation:

  • Depth - deep, fertile soils can support a wide range of vegetation while shallow infertile soils are limited in the range of vegetation they can support
  • Acidity - farmers spread lime on acidic soil to reduce its acidity and increase fertility
  • Drainage - clay soils can become easily waterlogged, becoming difficult to grow vegetation. Sandy soils are well drained so they can support a wide range of vegetation.
• Influence of vegetation on soil:

  • Plant litter - the vegetation provides plant litter for the soil, which becomes humus.
  • Soil erosion - vegetation binds the soil together, preventing soil erosion.
  • Leaching - the vegetation acts like an umbrella, in the way that it reduces the force of the impact of rainfall on soil. This reduces the process of leaching.