Salic Horizon - Soil Geography of the USA: A Diagnostic-Horizon Approach - page 226

The salt-affected areas of these deserts contain the following shrubs: black
greasewood ( Sarcobatus vermiculatus ), creosote bush ( Larrea tridentata ), salt-
bush ( Atriplex spp.), and the following shortgrasses: alkali sacaton grass
( Sporobolus airoides ), inland saltgrass ( Distichlis spicata ), wild rye ( Elymus
glaucus ), western wheatgrass ( Pascopyrum smithii ), and alkali bluegrass ( Poa
secunda ). Soils with salic horizons occur on gentle slopes, averaging between
0 and 3 %. Although 59 % of the soils are derived from alluvium, other common
parent materials include lacustrine (32 %) and marine deposits (6 %).
In the literature, topography is viewed as a very important factor leading to
the development of the salic horizon, including groundwater level and salinity,
slope position, proximity to the edge of playas, the presence of depressions, and the
influence of flooding (Table 20.5 ). Of the soil series in the USA containing salic
horizons, 38 % are somewhat poorly drained and 38 % are poorly drained. Parent
material is important, particularly where evaporites exist and in areas where dust is
deposited. All of the case studies examined occur in semiarid to hyperarid regions.
Humans have played an important role on modifying salic horizons through irrigation
and cropping. Few studies have addressed the time required to form a salic horizon.
Harris ( 1990 ) observed salic horizons forming on deltas in the Yukon Territory,
Canada, in as little as 100 years. In the Negev Desert, Israel, salts began accumulating
in the last one million years due to an increasingly aridic climate (Amit et al. 2011 ).

20.7 Genesis of Salic Horizons

The dominant processes leading to the development of saline soils are salinization,
gleization, and calcification, with silicification, gypsification, and argilluviation
occurring in some soils. The salts in soils with salic horizons in the USA originate
from evaporites, groundwater seeps, and dust deposition. In the USA, soils
containing salts more soluble than gypsum are classified into three broad classes,
sodic, saline, and saline-sodic, based on pH, electrical conductivity (EC), and
exchangeable sodium percentage (ESP) (United States Salinity Laboratory Staff
1954 ). Soils of the latter two classes may contain a salic horizon.
In that 89 % of the soil series with salic horizons in the USA contain an aquic
soil-moisture class, gleization is an important soil-forming process. This is further
evidenced by the masses of Fe or Mn and redox features commonly described in
salic soils of the USA. Calcification is evidenced by the abundance of CaCO 3 (mean
¼

13 %) in the
13 pedons (Table 20.1 ). In addition, five of these pedons have Bkz horizons, 11 %
of the soils with salic horizons occur in calcic or gypsic subgroups (Table 20.3 ), and
23 % of the 96 soil series contain a calcic horizon. Three of the 13 pedons for which
laboratory data are provided (Table 20.1 ) contain either an argillic horizon or have
duric properties; therefore, argilluviation and silicification are processes that only
infrequently accompany salic horizon formation in the USA.

12 %) and gypsum (CaSO 4 +2H 2 O) or anhydrite (CaSO 4 ) (mean ¼