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World’s Soil Resources

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GYPSISOLS (Gypsids)<br />

Gypsisols are characterized by a significant secondary accumulation of calcium sulphate. Accumulation<br />

of gypsum takes place initially as crystal aggregates in the voids of the soils. These aggregates grow<br />

by accretion, displacing the enclosing soil material. When the gypsic horizon occurs as a cemented<br />

impermeable layer, it is recognized as the petrogypsic horizon. These soils occur in the driest part of the arid<br />

climatic zone in unconsolidated deposits of base-rich weathering material on level land and in depressions.<br />

Natural vegetation on these soils is sparse and limited to xerophytes and ephemeral grasses and herbs<br />

(Figure A 24).<br />

The worldwide extent of Gypsisols has been estimated at about 100 million ha, exclusively occurring in<br />

desert areas. Major occurrences are found in the Near East, Kazakhstan, Turkmenistan, Uzbekistan, the<br />

Libyan and Namib deserts, in southern and central Australia and in the southwest of the United States.<br />

Large areas of Gypsisols are used for extensive grazing. When irrigation water is available these soils can<br />

be very productive, but the dissolution of gypsum results in the irregular subsidence of the land surface,<br />

caving in canal walls, and in the corrosion of concrete structures (FAO, 2014).<br />

Status of the <strong>World’s</strong> <strong>Soil</strong> <strong>Resources</strong> | Main Report Annex | <strong>Soil</strong> groups, characteristics,<br />

573<br />

distribution and ecosystem services

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