March, 1998 SCSB#391
Soil Mineral Associations Of The Southern United States
Abstract
This publication is the result of a regional research
effort to pool mineralogical data across the region in order to determine
ranges for occurrence of soil mineral suites, develop a classification
system for these mineral associations, and compile a map showing the distribution
of associations of soil mineral classes in the Southern Region.
Each participating state compiled mineralogical data obtained from samples
of control sections of extensive soils throughout the state. A mineralogy
composition code based on mineral dominance was adopted and states used
this code to report mineral composition, form criteria for mineral map
units and develop a state soil mineral map. The highest category
of this soil mineral assemblage classification has two classes, 1:1 dominated
and 2:1 dominated assemblages. The 1:1 dominated assemblages must not have
more than 10% smectite (no smectite detected by routine x-ray methods).
Assemblages dominated by 2:1 minerals without identifiable smectite are
separated. In the 2:1 class, the presence of free calcium carbonates is
considered an important differentiating characteristic. Free calcite in
soils controls mineral stability, nutrient availability, and other soil
reactions. Because of the important role of free calcium carbonate in soils
, it is considered differentiating class criterion at low concentration.
In 1:1 classes, levels of free iron oxyhydroxides and gibbsite are diagnostic.
In addition, weatherable minerals in the coarse fraction are used to form
classes. Nine soil mineral assemblage classes were defined. A nomenclature
was devised using names and elements from various sources. Soil mineral
assemblage map units were designed by using single assemblage names or
by grouping assemblages into associations. Twenty-five mineral map units,
an organic, unclassified and inland water were used.
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Document Prepared by:
Alabama Agricultural Experiment Station
Auburn University