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The most common engineering classification system for soils in North America is the Unified Soil Classification System (USCS). The USCS has three major classification groups: (1) coarse-grained soils (e.g. sands and gravels); (2) fine-grained soils (e.g. silts and clays); and (3) highly organic soils (referred to as "peat").
The Soil Taxonomy Forum is an online discussion site for the soil classification system. It is sponsored by USDA-NRCS and hosted by Virginia Tech University. The Forum encourages open discussion of topics related to soil classification, soil description, diagnostic soil properties and qualities of soil, taxonomic classes, and ideas to improve Soil Taxonomy.
Soil Genesis. Soil genesis or pedogenesis is the study of the origin and formation of soil. Pedologists conceptualize soil as a natural, three-dimensional body on the Earth's surface (Figure 2). This three-dimensional body, the pedon, is large enough to include all of the properties of the soil individual.
- Overview
- Soil classification
- U.S. Soil Taxonomy
The two principal systems of soil classification in use today are the soil order system of the U.S. Soil Taxonomy and the soil group system, published as the World Reference Base for Soil Resources, developed by the Food and Agriculture Organization (FAO) of the United Nations. Both of these systems are morphogenetic, in that they use structural properties as the basis of classification while also drawing on the five factors of soil formation described in the previous section in choosing which properties to emphasize.
Central to both systems is the notion of diagnostic horizons, well-defined soil layers whose structure and origin may be correlated to soil-forming processes and can be used to distinguish among soil units at the highest level of classification (see the table of primary diagnostic horizons). Diagnostic horizons may be found very near the land surface (epipedons) or deep in the soil profile (subsurface horizons); they need not correspond to the horizon letter designations.
The two principal systems of soil classification in use today are the soil order system of the U.S. Soil Taxonomy and the soil group system, published as the World Reference Base for Soil Resources, developed by the Food and Agriculture Organization (FAO) of the United Nations. Both of these systems are morphogenetic, in that they use structural properties as the basis of classification while also drawing on the five factors of soil formation described in the previous section in choosing which properties to emphasize.
Central to both systems is the notion of diagnostic horizons, well-defined soil layers whose structure and origin may be correlated to soil-forming processes and can be used to distinguish among soil units at the highest level of classification (see the table of primary diagnostic horizons). Diagnostic horizons may be found very near the land surface (epipedons) or deep in the soil profile (subsurface horizons); they need not correspond to the horizon letter designations.
The U.S. Soil Taxonomy classifies soils within a hierarchy of six categories. Only the highest-level category, order, is discussed here. Soil orders are named by adding the suffix -sol to a root word, as shown in the table of the U.S. Soil Taxonomy. The resulting 12 soil order names thus represent a classification based either on parent material or on processes related to the five factors of soil formation as reflected in diagnostic horizons.
The soil orders associated with specific kinds of parent material (Andisol, Histosol, and Vertisol) account for less than 5 percent of Earth’s continental areas covered by soil. Soils that show little development because they are too young (Entisol) or lie in an adverse weathering environment (Inceptisol) represent nearly 33 percent of the land area. Soils that are likely to exhibit natural toxicity to agricultural plants because of accumulations of salts (Aridisol) or of acidity and aluminum (Spodosol, Oxisol, and Ultisol) make up almost 40 percent of the total. This leaves essentially only the Alfisols and Mollisols—with about 15 percent of the total land area—as the inherently more fertile soils of the world. They occupy a strategic belt at middle latitudes in the Northern Hemisphere and in South America.
- Garrison Sposito
Soil” as well. State soils are soils with a special historical or agricultural significance for the state. Some are also named because of their extent or special location in the state. Poster produced by the Soil Science Society of America 5585 Guilford Road, Madison, WI 53711-5801 | www.soils.org Photos: Soil Profiles, USDA-NRCS.
Aug 5, 2016 · The names Atterberg, Casagrande and Terzaghi are well versed in the soil mechanics industry. Back in the fall of 2014, Tracy Barnhart wrote a wonderful article on the ‘ Three Musketeers in Soils Testing: Atterberg, Casagrande, and Terzaghi ’. This summer, we have decided to expand on the works of one individual in particular, Casagrande ...
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USDA Soil Taxonomy. This original “national” USA soil classification system - Keys to Soil Taxonomy, Twelfth Edition (2014) - has found widespread international acceptance particularly in countries in Latin America and Asia. The principles that were developed by Soil Taxonomy were taken up by WRB and the FAO Legend to set international ...
