Chapter 5

• Soil Classification & Taxonomy


  The classification and naming of soils

  
• Learning Objectives


  • Explain why there is need to classify soils
  • Discuss and enumerate six hierarchy of soil taxonomy
  • Enumerate and describe the different soil orders
• Humans tend to classify and categorize almost everything we encounter in our natural world
• Classification systems and taxonomic conventions allow us to describe a thing or phenomenon in a way that can then be understood by those in remote locations and without direct experience of the subject
• The soil forming factors of parent material, climate, vegetation (biota), topography, and time tend to produce a soil that describes the environment in which it is formed

  
• Soil


  A natural body comprised of solids (minerals and organic matter), liquid, and gases that occurs on the land surface

  
• Epipedon


  A horizon that forms at or near the surface and in which most of the rock structure has been destroyed
• Soil Taxonomy


  A basic system of soil classification for making and interpreting soil surveys

  
• Soil is not uniformly distributed. Properties of soil vary due to several soil forming factors
• Soil Classification


  The grouping of soils with a similar range of properties (chemical, physical and biological) into units that can be geo-referenced and mapped

  
• The World Reference Base (WRB) is the international standard for soil classification system endorsed by the International Union of Soil Sciences
• Basic Terms


  • alluvium
  • anaerobic
  • B horizon
  • permafrost
  • soil taxonomy
  • USDA Soil Classification System

  
• USDA Soil Taxonomy Hierarchy


  • Order
  • Suborder
  • Great Group
  • Subgroup
  • family
  • Series
• This system of soil classification provides information that can be used by land managers to make inferences regarding a particular soil's utility for plant production, urban/residential usages, waste management, and construction sites

  
• Soil Orders


  • Alfisol
  • Aridisol
  • Entisol
  • Histosol
  • Inceptisol
  • Mollisol
  • Oxisol
  • Spodosol
  • Ultisol
  • Vertisol

  
• Soil Series


  The most used unit of soil classification, determined by studying the horizon characteristics

  
• All soils given the same soil series name would possess the same characteristics across the landscape
• Examples of Soil Series

  • Holdrege
  • Nora
  • Sharpsburg
  • Valentine

  
• A soil series, type and phase name might be, for example: Sharpsburg silty clay loam, 5 to 9 percent slope, eroded

  
• Taxonomic Classification of Soils


  • Order
  • Suborder
  • Great Group
  • Subgroup
  • family
  • Series
• Soil name


  Comparable to a person's given name
• Nan's given name


  Nancy Marie Wilson Johnson
• Valentine soil's given name

  Valentine loamy fine sand, rolling, mixed, mesic, Typic Ustipsamment
• Categories of soil classification


  • Order
  • Suborder
  • Great Group
  • Subgroup
  • Family
  • Series
• Order


  • Differences among orders reflect the dominant soil forming processes and the degree of soil formation
  • Each order is identified by a word ending in 'sol'
  • Example: Alfisols

  
• Suborder


  • Divided primarily on the basis of properties that influence soil formation and/or are important to plant growth
• Great Group


  • Divided on the basis of similarities in horizons present, soil moisture or temperature regimes, or other significant soil properties

  
• Subgroup


  • Each great group has a 'typic' (typical) subgroup
  • Other Subgroups are transitions to other orders, suborders, or great groups due to properties that distinguish it from the great group
• Family


  • Established within a subgroup on the basis of physical and chemical properties along with other characteristics that affect management
• Series


  • Consists of soils within a family that have horizons similar in color, texture, structure, reaction, consistence, mineral and chemical composition, and arrangement in the profile

  
• Soil names are derived from Latin and English
• Soil orders


  • Entisols
  • Inceptisols
  • Aridisols
  • Mollisols
  • Alfisols
  • Spodosols
  • Ultisols
  • Oxisols
  • Gelisols
  • Histosols
  • Andisols
  • Vertisols

  
• Entisols


  • Soils with little profile development
  • Many different parent materials contribute to varied soil properties
  • Often found in very dry or cool locations
  • Widely varied productivity potential
• Inceptisols


  • The beginnings of soil profile development
  • Color differences between horizons starting to show
  • Prominent in mountainous areas, but occur almost everywhere
  • Widely variable productivity potential

  
• Aridisols


  • Soils of arid, desert climates
  • Often have accumulations of lime (CaCO3), sodium, or salts
  • Can be made productive if irrigation water is available
  • Found extensively in tropical latitudes, rainshadows, and arid climates
• Mollisols


  • Mineral soils developed under grassland vegetation
  • Thick, dark-colored 'A' horizon, rich in organic matter
  • Generally very fertile for plant growth due to clay and organic matter content
  • Considered to be among the most fertile soils on Earth

  
• Alfisols


  • Found under forest and savanna vegetation
  • Clay accumulations in subsoil horizons
  • Often are leached below topsoil (E horizon)
  • Generally fertile, with high base saturation%

  
• Soil Taxonomy is the most specific classification for soils

  
• Holdrege silt loam


  Fine-silty, mixed, mesic, Typic Argiustoll
• Based on its taxonomy, the Holdrege soil is a silty grassland soil with some clay, derived from several clay minerals, a thick dark organic-rich surface soil and an accumulation of clay in the subsoil that developed under a relatively cool dry climate with limited rainfall occurring during the spring and summer