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For the other part, they show us why, in the field, Vertisols and
Solonetz occur in close association. In both, 2/1 clay minerals are formed
but are degraded by alkalinolysis only in Solonetz. Such association
is seen in Sudan or in the low portion of the glacis of Chad (Paquet
et al
. 1966). We have mentioned this earlier (Chap. 6, ยง 6.6). In this
case, the solodized Solonetz occupy positions a few decimetres lower,
while Vertisols occupy micro-buttes. This is not surprising (descent
of soil surface linked to degradation). Also, the carbonates carried by
runoff waters can spread only in the depressions, where they strengthen
alkalization.
13.5.2 Grouping of Saline Soils in The WRB
The WRB does not have a generic term for saline soils and directly
distinguishes
Solonchak
and
Solonetz
.
tchaks)
The name comes from the Russian
sol
(salt) and
chak
(saline land). The
resemblance to the English
chalk
is, therefore, only fortuitous and a little
annoying for all these soils are not calcareous. These are saline soils in
which the 2/1 clay minerals are stable and in flocculated condition (good
structure). The profile is scarcely differentiated, of AC type. Solonchaks
are characterized by a
salic
horizon. This horizon has an electrical
conductivity of 15 mmhos/cm in the saturated-paste extract; the limit
is lowered to 8 mmhos/cm in the case of very alkaline or very acid
soils. But, as we have said, the threshold is lowered to 4 mmhos/cm in
certain classification systems.
Calcic Solonchaks
and
Solonchaks
Calcaric
are rich in Ca
2+
and often
Mg
2+
. Sodium forms <15 per cent of the CEC in them. In their case,
eventual desalinization does not lead to profound change in physical
properties. These soils are often found in steppe regions or continental
subdesertic regions, where salts are concentrated through evaporation.
They often have a white encrustation on the surface.
Solonchaks
Sodic
are soils poor in Ca
2+
and Mg
2+
, with the proportion
of Na
+
on the exchange complex exceeding 15 per cent. These are,
therefore, saline soils with sodic exchange complex. They are often
linked to the presence of the sea and are, in particular, lagoonal soils
of the European Atlantic coast.
On the Mediterranean coast (Servant 1974), they present a hygroscopic
encrustation based on chlorides on the surface.
Solonchaks (earlier Solon
