Chapter 3

Soil Classification

(book excerpts)

To identify, understand, and manage soils, soil scientists have developed a soil classification or taxonomy system. Soil classification concerns the grouping of soils with a similar range of properties (chemical, physical, and biological) into units that can be geo-referenced and mapped. The most widely-used classification system is the Soil Taxonomy system that was made known by the United States Department of Agriculture (USDA). Soil Taxonomy classifies a soil according to its observable and measurable properties. The properties that are observed and measured include morphological, physical, chemical, and mineralogical properties. The morphological properties are horizon differentiation, soil depth, etc.; the physical properties include color, texture, structure, compaction, etc.; and the chemical and mineralogical properties include organic matter, pH, base saturation percentage, clay, iron and aluminum oxides, and silicate clays of different horizons or layers. The soil-forming factor “climate” has a predominate role in Soil Taxonomy classification, followed by parent material, and soil biota; topography and time are not utilized in defining taxa. Unlike taxonomy for plants and animals, soil classification is not universal. While the USDA’s Soil Taxonomy can be universally applied to the soils of the globe, outside the United States, many nations employ their own systems to serve their own purposes. A common application of soil classification (the act of identifying the taxonomic classification for a given soil) is to develop models of how soils of different classifications associate with one another within a landscape, which can eventually be used in soil mapping.

Click on the following topics for more information on soil classification.

Topics Within This Chapter:

  • Soil Taxonomy System
  • Soil Orders
  • Alfisols
  • Andisols
  • Aridisols
  • Entisols
  • Gelisols
  • Histosols
  • Inceptisols
  • Mollisols
  • Oxisols
  • Spodosols
  • Ultisolss
  • Vertisols
  • Suborder, Great Group, Subgroup, Family, and Series
  • Soil Surveys
  • Soil Survey Components
  • The Pedon, a Unit of Sampling
  • Limitations of Soil Surveys
  • Web Soil Survey
  • Soil Maps
  • Land Capability Classes
  • Capability Classes