Alkali soil

[Sarah]

Any one of various soils found in arid and semiarid regions,containing an unusual amount of soluble mineral salts whicheffloresce in the form of a powder or crust (usually white) in dryweather following rains or irrigation. The basis of these salts ismainly soda with a smaller amount of potash, and usually a littlelime and magnesia. Two main classes of alkali are commonlydistinguished: black alkali, which may be any alkaline carbonate, butwhich practically consists of sodium carbonate (sal soda), which ishighly corrosive and destructive to vegetation; and white alkali,characterized by the presence of sodium sulphate (Glauber's salt),which is less injurious to vegetation. Black alkali is so calledbecause water containing it dissolves humus, forming a dark-coloredsolution which, when it collects in puddles and evaporates, producescharacteristic black spots.