SOIL SCI 602: Soil Orders

• Gelisols


  Soils of very cold climates that contain permafrost within two meters of the surface
• Gelisols


  • Limited geographically to the high-latitude polar regions and localized areas at high mountain elevations
  • Support only approximately 0.4 percent of the world's population — the lowest percentage of any of the soil orders
  • Frozen condition makes them sensitive to human activities
• Gelisol suborders


  • Histels
  • Turbels
  • Orthels
• Histosols


  Soils that are composed mainly of organic materials, containing at least 20-30 percent organic matter by weight and more than 40 cm thick
• Histosols


  • Bulk densities are quite low, often less than 0.3 g cm3
  • Physical properties restrict their use for engineering purposes, including low weight-bearing capacity and subsidence when drained
• Histosol suborders


  • Folists
  • Wassists
  • Fibrists
  • Saprists
  • Hemists
• Histosols form in settings such as wetlands where restricted drainage inhibits the decomposition of plant and animal remains, allowing these organic materials to accumulate over time
• Histosols are ecologically important because of the large quantities of carbon they contain
• Spodosols


  Acid soils characterized by a subsurface accumulation of humus that is complexed with Al and Fe
• Spodosols


  • Typically form in coarse-textured parent material and have a light-colored E horizon overlying a reddish-brown spodic horizon
  • The process that forms these horizons is known as podzolization
  • Many Spodosols support forest
  • Naturally infertile, require additions of lime in order to be productive agriculturally
• Spodosol suborders


  • Aquods
  • Gelods
  • Cryods
  • Humods
  • Orthods