USDA Soil Taxonomy

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As USDA Soil Taxonomy is called a soil classification system , which the US Department of Agriculture ( US Department of Agriculture , USDA - Natural Resources Conservation Service , NRCS) issued. The Soil Taxonomy was mainly developed by Guy D. Smith. Based on a design from 1960, the first edition of the Soil Taxonomy followed in 1975 and the second edition in 1999. The Keys to Soil Taxonomy, each with minor changes, is published at shorter intervals. The 12th edition of the Keys to Soil Taxonomy from 2014 is currently valid.

In addition to the FAO soil classification that is no longer used and the World Reference Base for Soil Resources (currently: 3rd edition 2014, update 2015), the Soil Taxonomy is one of the most important classification systems for soils in use worldwide.

The Soil Taxonomy divides floors for a combination of soil-forming factors, the climate is given a special meaning, but in many cases even after a purely pragmatic point of view, in twelve orders ( orders ), which are given below:

  • Alfisols show clay enrichment in the subsoil and a high base saturation . Their main area of ​​distribution is in the moderate latitudes.
  • Andisols are soils with allophanes or aluminum-humus complexes. Many were created by weathering from volcanic glass .
  • Aridisols are desert soils that show at least some soil development, often the accumulation of easily soluble salts, gypsum or carbonate.
  • Entisols are very young soils with little noticeable leveling. All soil types that cannot be assigned to any of the other orders are assigned to this category.
  • Gelisols are characterized by permafrost , which begins at the latest at a depth of two meters. The largest permafrost areas are found in the boreal and polar zones of the northern hemisphere.
  • Histosols have powerful organic horizons. These include in particular the moors, which develop specifically in cool, humid climates.
  • Inceptisols are young soils which, however, already show some soil development and occur on young land surfaces all over the world.
  • Mollisols show mineral topsoils that are dark and relatively humus-rich and have a high base saturation . They occur especially in the dry middle latitudes under steppe climates.
  • Oxisols are heavily weathered soils that are dominated by kaolinite and oxides. They are particularly widespread in the tropics, are poor in nutrients and often colored red by hematite .
  • Spodosols show an accumulation of aluminum, iron and humus in the subsoil. They are strongly acidic and typically occur on sandy substrates in cool, humid regions under conifers and dwarf shrubs.
  • Ultisols show clay enrichment in the subsoil and low base saturation . Its main area of ​​distribution is in the tropics and subtropics.
  • Vertisols have high contents of swellable and shrinkable clay minerals and occur in humid climates from the tropics to the temperate latitudes.

The orders received will be hierarchically continue in submissions ( suborders ), supergroups ( great groups ) and subgroups ( subgroups divided). Additional subunits are families ( families ) and rows ( series ). The detailed system can be found in the respective sub-articles.


  • Soil Survey Staff: Soil Taxonomy: A Basic System of Soil Classification for Making and Interpreting Soil Surveys. 2nd edition. Natural Resources Conservation Service. US Department of Agriculture Handbook 436.Washington DC, USA, 1999.
  • Soil Survey Staff: Keys to Soil Taxonomy. 12th edition. Natural Resources Conservation Service. US Department of Agriculture. Washington DC, USA, 2014.

Web links

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