Soils

• What is soil

  Soil is a mixture of organic matter, minerals, gases, liquids, and organisms that all support life
• Soil Horizons

  • Weathering leads to the creation of soil horizons
  • Soil formation is an open system
  • There are multiple horizons in soils, with forest soils being the most diverse
  • Soil production experiences a wide range of biological, chemical and physical processes
  • Soil horizons vary by country or system, despite this they all provide essential nutrients for primary life
• Formation of Soil


  • Soil is formed through decomposition; this includes processes of mineralisation and humification.
  • Mineralisation- Oxidation of organic matter to inorganic forms of nutrients
  • Humification – Transformation of organic matter into stable organic compounds
  • Formation of soil is only possible if the formation of soil rate is faster than the erosion rate
  • Global average rate of formation of soil = 144mm per 1,000 years
• Drivers of Soil formation

  • Humans, lithology, climate, vegetation, time and topography all influence soils
  • Due to this the chemical and physical properties of soils change over time:

  o   Thickness

  o   Horizons

  o   Colour

  o   Biology

  o   Chemistry
• Forest Soil horizons

  In forest and grassland environments- precipitation, dust, flood deposits and organic matter are added to the soils to provide diverse horizons
• Arid and semi-arid horizons


  • In arid and semi-arid environments- dust and precipitation are the additions to soil. Due to the lack of organic matter, carbonate horizons are formed
  • Subsurface enrichment of carbonate via dust, rainwater and vegetation contributes to soil formation
  • Rainwater carries this carbonate further into the soil where it precipitates
  • This forms duricrusts which exhibit rock properties despite being a soil horizon
• Preservation of Soils

  • Soils are formed and preserved in intermediate zones which experience low levels of active processes
  • The formation of new soil is useful in preserving old soils (paleosols)
  • Paleosols Allow for environmental and landscape reconstruction as they reflect a window of past time. E.g., in a rainforest environment soil gets well preserved and is a great window into past pollen, micro fossils or phytolith information