one of the 30 soil groups in the classification system of the Food and Agriculture Organization (FAO) (soil). 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 evaporation—conditions 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.