SOLONCHAK

one of the 30 soil groups in the classification system of the Food and Agriculture Organization (FAO). Solonchaks are defined by high soluble salt accumulation within 30 cm (1 foot) of the land surface and by the absence of distinct subsurface horizonation (layering), except possibly for accumulations of gypsum, sodium, or calcium carbonate or layers showing the effects of waterlogging. Solonchaks are formed from saline parent material under conditions of high evaporationconditions encountered in closed basins under warm to hot climates with a well-defined dry season, as in arid, Mediterranean, or subtropical zones. Occupying about 2.6 percent of the continental land surface on Earth, they are found principally in Chad, Namibia, Australia, Paraguay, and Uruguay. Owing to their high soluble salt accumulations, Solonchaks require irrigation and drainage if they are to be used for agriculture. They are similar to the salinized soils in the Aridisol order of the U.S. Soil Taxonomy. Related FAO soil groups originating in arid climates and subject to limited leaching are the Solonetz, Durisols, Gypsisols, and Calcisols.