Geoscience Reference
In-Depth Information
Solonchaks are poorly drained soils having low hydraulic conductivity and high
concentrations of soluble salts within their profi les. Their existence is restricted to
arid and semiarid climatic zones, and they appear only exceptionally in coastal
areas. The high concentration of salts is refl ected by their name from the Russian
sol
which means salt. The parent rocks of these soils are unconsolidated materials.
Since the potential evaporation is substantially higher than the average annual pre-
cipitation, the dominant direction of water fl ow is upward and the fl owing water
simultaneously carries dissolved salts - the products of weathering. As the water
evaporates, those salts remain in the topsoil horizons, some of which eventually
precipitate as a whitish powder just on the surface. The salinization process is con-
ditioned by the depth of the groundwater table. When the water table is below the
bottom of a soil profi le, salinization is relatively slow. On the other hand, saliniza-
tion is accelerated when the water table rises into a soil profi le that eventually devel-
ops distinctly visible gleyic marks within its horizons. Greater accumulations of salt
occur in low-lying topographic areas owing to their transport from shallow water
tables. If soils of arid and semiarid regions are irrigated, salinization is a potential
hazard even in the absence of a groundwater table. Carefully performed sprinkler
and drip irrigation methods have the potential to restrict or completely avoid salini-
zation and Solonchak development. Using irrigation water containing low amounts
of salts is also an important prevention of salinization. Certain plants evolved in arid
and semiarid zones, like cotton, resist soil salinity, and even thrive up to a threshold
value. But for even these plants, their yields decrease whenever the soil salt content
rises permanently above this threshold value. Solonchaks are excluded from agri-
cultural use after their salt contents cross a critical value defi ned for a group of
selected plants in a specifi c, local environment. A traditional weapon against salini-
zation is fl ush irrigation - the repetitive application of excessive amounts of water
to create a vertical downward fl ux during a selected time period to adequately fl ush
deleterious salts out of the soil profi le. The weapon has to be used judiciously, i.e.,
it has to be accompanied with intensive drainage, allow an aftermath of the ground-
water table being at a desired critical depth below the root zone, and connect with a
successful method of transporting the salty drain water to another acceptable loca-
tion at or below the surface of the landscape. In old national systems we could fi nd
Alkaliböden or Weissalkaliböden, Saline Soils, White Alkali Soils, or Salt-Affected
Soils. They belong to Orthids in the order of Aridisols and to several taxons of low
taxonomic level of Entisols in the US Taxonomy.
Solonetz is soil with a high content of exchangeable Na
+
and Mg
2+
ions that cre-
ate an alkaline pH reaction of about 8.5. The name again derived from the Russian
sol
which means salt and coupled with
nec
which means expression of a negative
property obviously refers to unfavorable soil physical characteristics for cultural
plants, e.g., destruction of soil structure, strong swelling and shrinkage, and an
extremely low hydraulic conductivity within the horizon having a high percentage
of exchangeable Na
+
and Mg
2+
. The concentration of soluble salts in top horizons is
substantially lower than that in Solonchak because they were washed out. This con-
dition could be an alternative nuance of the Russian
nec
indicating that there are no
more soluble salts of high concentration, i.e., a negative of salts. Na
+
and Mg
2+
were
