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In the USA, most research on soils with calcic and petrocalcic horizons has been
conducted in the southwest, although some research has been conducted in other
parts of the country. There is a debate in the literature as to the relative importance
of aeolian contributions versus weathering of calcareous materials to produce
pedogenic carbonates, and also the extent and distribution of these soils has not
been properly assessed.
12.2 Properties of Calcic and Petrocalcic Horizons
Examples of soils with a calcic and petrocalcic horizon are given in Fig. 12.1 .
Based on the investigation of 201 pedons from the SSURGO database, the
average depth to the calcic horizon was 38 cm but ranged from 0 to 145 cm.
The average thickness of the calcic horizon was 73 cm, with a range of 15
(minimum required) to 229 cm (Table 12.1 ). The mean carbonate stage was 1.8,
indicating the presence of carbonate nodules and continuous coatings beneath
clasts. The mean reaction of calcic horizons to 10 % HCl was very strong
(class 3.2).
The average thickness of the petrocalcic horizon was 60 cm (based on
32 pedons), with a range of 11 to 183 cm (Table 12.1 ). The average depth to the
calcic or petrocalcic horizon was 32 cm, ranging from 3 to 91 cm. The mean
carbonate stage was 4.3, indicating platiness, moderately developed laminae, strong
cementation, case hardening, and some scattered pisoliths. The mean reaction of
calcic horizons to 10 % HCl was violent (class 4).
12.3 Classification of Soils with Calcic and Petrocalcic
Horizons
Soils with calcic and petrocalcic horizons could be taxonomically identified in six
orders, 22 suborders, 46 great groups, 158 subgroups, and about 2,200 soil series
(Table 12.2 ). Soil series with calcic or petrocalcic horizons were most abundant in
the Aridisols and Mollisols. There are also soil series in the Inceptisols, Alfisols,
Vertisols, and Andisols that have calcic or petrocalcic horizons. There are no soil
series in the NRCS database with a calcic horizon in the Gelisols although
such soils are known to exist (Calcic Anhyorthels and Anhyturbels). The criteria
for identifying Entisols, Histosols, Oxisols, Spodosols, and Ultisols (Soil Survey
Staff 2010 ) preclude them from having a calcic horizon.
The mesic, frigid/cryic, thermic soil-temperature regimes accounted for 36 %,
35 %, and 23 % of all soil series with a calcic or petrocalcic horizon (Fig. 12.2 ). The
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