Salic Horizon - Soil Geography of the USA: A Diagnostic-Horizon Approach - page 217

Silt was the dominant particle-size fraction in salic horizons, averaging 42 % of
the fine-earth ( 2 mm) fraction (Table 20.1 ). The mean bulk density was 1.4 g/cm 3 .

Salic horizons in dominant soil series of the National Soil Survey Laboratory
(NSSL) database are strongly alkaline due to the presence of calcium or sodium
carbonate. The mean pH of the salic horizon is 8.5, with values ranging from 7.4 to
10.5. The mean SAR is 161, and the mean EC of the salic horizon is 40 dS/m. In the
salic horizon, calcium carbonate and gypsum average 12 and 13 %, respectively.
Cation-exchange capacity of the salic horizon is moderate, reflecting the abundance
of clay (mean ¼ 25 %) and organic C (mean ¼ 0.5 %). The base saturation (data not
shown) is 100 % for all pedons, with Ca and Na dominating the exchange sites.
Mineralogy of soils with salic horizons are reported for the

<

2 m clay fraction

< μ

(seven soil series), the 50-20 m coarse-silt fraction (three soil series), and the 100-

μ

50 m very-fine-sand fraction (one soil series). The clay fraction contains primarily

illite group minerals, kaolinite, smectite, and quartz; glass and sponge spicules are
common in the coarse-silt fraction; and a variety of minerals are present in the very-
fine-sand fraction (Table 20.2 ). These data are corroborated by the fact that the
mineral class is commonly mixed. The dominant salts are halite (NaCl) and trona
(NaHCO 3 +Na 2 CO 3 -2H 2 O), with carbonate flecks and gypsum fibers also being
common.

μ

20.3 Classification of Soils with a Salic Horizon

Soils with a salic horizon occur in two orders, two suborders, three great groups,
11 subgroups, and 96 soil series (Table 20.3 ). Soil series with a salic horizon are
most abundant in the Inceptisols (62), followed by the Aridisols (35). Soils with a
salic horizon are recognized in the Alfisols (Salidic Natrustalfs), Gelisols (Salic
subgroups of Anhyorthels, Aquorthels, and Anhyturbels), Inceptisols (Salidic
Sulfaquepts), Mollisols (Salidic subgroups of Calciustolls and Haplustolls), and
Vertisols (the surborders Salaquerts, Salitorrerts, and Salusterts), but no soil series
have been officially recognized in these orders. However, it is likely that soil series
included in these orders contain a salic horizon but that the horizon is secondary in
the classification of the series.
Of the 96 soil series with a salic horizon 50 % have a mesic and 19 % have a
thermic soil-temperature class, 89 % have an aquic soil-moisture class, 79 % have
a mixed mineralogy class, 52 % have a calcareous reaction class, 59 % have a
superactive cation-exchange activity class, and 24 %, 24 %, and 19 % have a fine,
fine-loamy, or fine-silty particle-size class, respectively.
Soils with a salic horizon predominantly contain an ochric epipedon (98 % of
pedon descriptions); subsurface horizons present in soils with a salic horizon
included the calcic (24 % of pedons), cambic (18 %), gypsic (11 %), and duric
(7 %), argillic (4 %), and natric (2 % of pedons).