Geoscience Reference
In-Depth Information
13
Saline Soils: Solonchaks and
Solonetz
INTRODUCTION
Saline salts contain salts more soluble than gypsum, that is, those liable
to enter the soil solution in quantities large enough to restrict plant
growth. Consequently, calcareous soils are not saline soils, although
calcium carbonate is chemically a salt like any other.
Salinization is spreading. In eighteen centuries, Mesopotamia has
lost most of its capability to produce wheat. Pakistan is losing 100 ha of
cultivable land a day. In India, one-tenth of the irrigated area is affected.
In all, ten million ha will be rendered sterile by salt every year in the
world (Szabolcs 1994)! But scientists give different global balance sheets.
According to FAO, soils already salinized represent two per cent of the
world land surface, or nearly 300 million ha. Other specialists suggest
double or triple this number. Salinization will affect 20 to 50 per cent of
the irrigated land in the world (Kovda 1977). The arid countries (Egypt,
West Asia, Australia, etc.) are threatened.
It is therefore essential to examine saline soils and the problems
relating to them. This time around, we modify the timescale. It is
necessary to think in terms of the year and, sometimes, of the season
and give up almost completely the arguments that we earlier applied
and which came within the scope of thousands or even millions of
years.
13.1 EXPRESSION OF SALINITY
The quality of irrigation water depends on many factors, particularly
(USDA 1954):
