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Classification, Properties, and Management of Aridisols

Suborders and Great Groups

Aridisols Slide 29

In addition to diagnostic horizons and soil moisture regimes, ten soil temperature regimes are very important for classification of soils in Soil Taxonomy. For example, one of the seven suborders of the Aridisol Order is differentiated by the upper boundary of the cryic soil temperature regime, 0º to 8º C. Cryids are Aridisols with soil temperatures between 5º and 8º C, 5º is the lower temperature limit of Aridisols, 8º is the upper limit of cryic soil temperature regime. The Suborders of Aridisols have undergone major changes since the 1975 edition of Soil Taxonomy. Originally there were only two Suborders, Argid which still remains and Orthid which has been deleted, its soils placed into new classes. Argids are differentiated by the presence or absense of horizons having silicate clay enrichment. Argids have argillic or natric horizons. Orthid was a catch-all class that lacked horizons of clay enrichment. For the reclassification of Suborders, many of the diagnostic horizons that were used to differentiate Argids and Orthids at the next lower taxonomic level (Great Group) were elevated to Suborder criteria.

Aridisols Slide 30

The next level of Soil Taxonomy is the Great Group. Great groups represent subdivisions of suborders based on similar kind, arrangement, and degree of expression of horizons. For example, the six Argid Great Groups are differentiated by the amount of clay in the argillic horizon and by the type of associated subsurface diagnostic horizons. Argid Great Groups have also been modified since the 1975 edition of Soil Taxonomy. Two Great Groups have been deleted, Durargids and Nadurargids. Three Great Groups have been added, Petroargids, Gypsiargids, and Calciargids.

Introduction to Aridic Soils | Soil Taxonomy | Introduction to Soil Horizons | The Horizons | Suborders and Great Groups | Argid Suborder | Orthid Suborder | Subgroups | Families | Non-Aridisols | Irrigation | Saline Soils | Sodic and Saline-Sodic Soils | Final Considerations

URL:http://cals.arizona.edu/OALS/soils/aridsoils/suborders.html
Last revised: 29 August 2001
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