Soil Classification

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Soil classification is the process of categorizing soils into different groups or classes based on their properties and characteristics. It is essential for understanding and managing soil resources, agricultural practices, and environmental conservation. Various soil classification systems exist worldwide, each tailored to specific purposes and regions. The two most widely used soil classification systems are the United States Department of Agriculture (USDA) Soil Taxonomy and the World Reference Base for Soil Resources (WRB). Let's briefly explore these two systems:

USDA Soil Taxonomy:

The USDA Soil Taxonomy is primarily used in the United States and is based on soil properties, including soil texture, mineral composition, color, structure, and other diagnostic criteria. It classifies soils into six hierarchical categories called soil orders, suborders, great groups, subgroups, families, and series. Each level represents a more specific classification based on increasing similarities in soil properties. The six soil orders in the USDA Soil Taxonomy are:

  • Entisols: Young, poorly developed soils with little or no horizon development.
  • Inceptisols: Moderately developed soils with some horizon development but not enough to be classified as other soil orders.
  • Andisols: Soils formed from volcanic materials, rich in amorphous materials like allophane and imogolite.
  • Gelisols: Soils with permafrost within two meters of the surface.
  • Histosols: Organic soils with high organic matter content, typically found in wetlands.
  • Aridisols: Soils found in arid regions with limited horizon development due to dryness.

World Reference Base for Soil Resources (WRB):

The WRB is an international soil classification system developed by the International Union of Soil Sciences (IUSS). It is designed to be applicable worldwide and considers soil properties, soil genesis, and environmental conditions. The WRB classifies soils based on diagnostic horizons, soil properties, and other characteristics. The WRB recognizes 32 reference soil groups, which are then grouped into higher-level categories based on similarities.

Both the USDA Soil Taxonomy and the WRB provide a systematic approach to soil classification, facilitating communication among soil scientists and professionals worldwide. These classification systems help in soil mapping, land use planning, and sustainable soil management practices. It is important to note that soil classification is an evolving field, and new information and research may lead to updates and refinements in classification systems over time.