Salic Horizon - Soil Geography of the USA: A Diagnostic-Horizon Approach - page 224

20.5 Comparison of Salic Horizon Properties in USA
with Other Areas

There are only scattered pedons with salic horizons reported in the literature, with the
exception of Spain (Table 20.4 ). The depth to the salic horizon ranged from 0 cm in
Iran and Israel to 26 cm in Somalia, as compared to a value of 5 cm for the USA. The
thickness of the salic horizon ranged from75 to 170 cm and averaged 83 cm for soils

with salic horizons in the USA. Clay concentrations ranged from 7.2 % to 42.0 % and
averaged 25.4 % in the USA. The low clay values in the Negev desert of Israel can be
attributed to the sandy eolian and fluvial materials. Silt concentrations ranged from
20.0 % in Israel to 72.0 % in Hungary and averaged 42.4 % in the USA. The abundant
clay and silt in soils with salic horizons is due to the fact that these soils often form in
playas. The mean bulk density of salic horizons in USA soils was 1.4 g/cm 3 ,whichis
lower than the 1.58-1.60 g/cm 3 values reported in salic soils of Israel and Hungary,
reflecting the maintenance of ped structure.
The mean pH of soils with salic horizons generally varied from 7.3 to 8.9 and
was 8.5 for US soils (Table 20.4 ). The low value (5.0) for soils with a salic horizon
in Ghana can be attributed to the existence of pyrites in the sediments. The high
values (10.0) in Russia are related to the sodicity of the soils. Soil organic C values
ranged from 0.11 % to 1.0 %, as compared to a mean value of 0.52 % for salic
horizons in the USA. Cation-exchange capacities ranged from 15.8 to 48.3 cmol(+)/
kg soil, with values for salic horizons in the USA toward the low end of the range at
17.1 cmol(+)/kg soil. The SAR of soils with a salic horizon ranged from 38 to
132, as compared to a mean value of 161 for US salic soils. The EC ranged from 5.1
to 53.9 dS/m, with a mean value of 40.2 for salic soils in the USA. Calcium
carbonate ranged from 11.5 % (Hungary) to 40.0 % (Iran); CaCO 3 was toward
the low end of the range in salic soils of the USA, averaging 12.3 %. There was
minimal data for gypsum concentrations; however, salic soils in the USA had
higher values (13.2 %) than salic soils in Spain and Iran. In general, salic horizons
in the USA were comparable with those of Hungary.

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20.6 Factors Influencing the Formation of Salic Horizons

In the USA, soils with salic horizons occur in variety of climates. The soil-
temperature class is dominantly mesic, but soils with thermic and frigid soil-
temperature regimes are common. The mean annual precipitation (MAP) averaged
300 mm/yr, but values ranged widely between 100 and 1,015 mm/yr (data not
shown). The mean annual air temperature (MAAT) averaged 12 C, but ranged
from 6 to 24 C (data not shown). The western USA is divided into four desert
regions based on rainfall distribution and amount, elevation, and other factors: the
Chihuahuan (southeastern AZ, southwestern TX), the Sonoran (southern CA and
southwestern AZ), the Mojave (southeastern CA), and the Great Basin (NV, UT,
OR, and portions of adjoining states).