Geoscience Reference
In-Depth Information
Additional soil orders could include the human-affected soils (Anthrosols), an
order combining all of the soils in Aqu- suborders (Gleysols and Stagnosols), soils
with a natric horizon (Natrisols), and possibly soils with a duripan (Durisols). The
WRB has 39 diagnostic horizons and ST has 27 (Table
27.1
). The WRB has
32 reference soil groups that are approximately equivalent to the 12 orders in ST
(Table
27.2
). Some of the existing orders in ST need additional suborders, espe-
cially the Gelisols. An Anhydrel suborder would address soils in hyper-arid regions
of Antarctica.
The use of diagnostic-horizon names at the subgroup level is confusing and
inconsistent. For example, soils in mollic subgroups must (1) meet all of the
requirements of a mollic (JAHE, p. 36, KST, 2010); (2) meet all of the requirements
except for thickness after mixing (JAHH, p. 36); (3) be
18 cm thick and meet the
color requirements after mixing (JADF, p. 43); (4) be
10 cm (unmixed) (JDGS,
p. 74); or (5) be
15 cm and meet the color requirements after mixing (LBHF,
p. 125). The use of Hum- at the subgroup levels allows mollic, umbric, or melanic
epipedons for Andisols and Inceptisols. At the great-group level, Hum- allows
mollic or umbric in Inceptisols and Oxisols.
The NRCS database is easy to work with and offers much potential in under-
standing the geography and genesis of soils. However, it would be useful to be able
to query all of the OSDs simultaneously to identify soil series with specific features,
such as the cambic horizon.
Reference
Webster R (1968) Soil classification in the United States: a short review of the Seventh Approx-
imation. Geogr J 134:394-396