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Classification, Properties, and Management of Aridisols

Subgroups

Aridisols Slide 45

The next level of soil taxonomy is the Subgroup. Subgroup names are Great Group names modified by one or more adjectives which denote how soils differ from the typical concept of the Great Group. As an example, we will look at a few of eighteen Subgroup classifications of the Haplargid Great Group (originally only four, Typic, Lithic, Ustollic and Vertic, in the 1975 edition).

Aridisols Slide 46

Haplargids are Argids that have weakly to moderately developed argillic horizons. Commonly, the lower parts of the argillic horizon have accumulations of carbonates as seen here. This Haplargid does not differ significantly from the central concept of the Haplargid Great Group. Thus, it is called a Typic Haplargid.

Aridisols Slide 47

Lithic Haplargids are like Typic Haplargids except that they have a lithic or bedrock contact within 50 cm of the soil surface. Lithic Subgroup classifications of Haplargids have been expanded in recent editions of Soil Taxonomy. Now there are also Lithic Ustic Haplargids, Lithic Xeric Haplargids, and Lithic Ruptic-Entic Haplargids classes. These soils are rarely developed for agriculture and are best managed as rangelands.

Aridisols Slide 48

Ustollic Haplargids have been deleted from the taxonomy. They were soils with more organic matter in the ochric epipedon than do soils of the original typic Subgroup and were an intergrade to soils in the Mollisol Order. The soils in this class have been reassigned by their moisture condition—that is transitional from aridic to the moister ustic soil moisture regime—and by other criteria. The new classes include Lithic Ustic Haplargids, Ustertic Haplargids, Arenic Ustic Haplargids, and Ustic Haplargids.

Aridisols Slide 49

Vertic Haplargids have been expanded to include two additional classes, Xerertic Haplargids and Ustertic Haplargids. They differ from Typic Haplargids by having cracks that remain open for 8 months or more in most years. These soils have high clay contents and are an intergrade to the Vertisol soil Order. These Haplargids can be agriculturally productive but, because of their high clay contents, they require special management practices.

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/subgroups.html
Last revised: 29 August 2001
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