According to investigations in California by Hilgard (1914) and in Hungary by Treitz (1908), these soils are found only upon loess and marl. [Nota de rodapé 2: The formation of the North America soda soils, according to Breazeale, is due ia many cases to the presence of a lime crust in a sodium chloride soil (cf. also Dorsey, 1906).] The deciding factor for their formation is, according to Treitz, whether or not precipitation water drains off from the soil. If the water does not drain off, the alkali salts collect as a residue in the soil depressions. When the sulphates and chlorides in solution penetrate the porous Hme soil (sodium formation is possible only upon soils rich in lime), the calcium goes into solution as bicarbonate; this reacts with the sodium salts forming alkaline salts of carbonic acid, while the lime unites with the sulphuric and hydrochloric acids. (Braun-Blanquet 1932:204)
During the rainy season the sodium carbonate dissolved in the soil water passes from the upper layers of soil to the lower. Here it meets with crystallized gypsum and is changed to sodium sulphate. When the dry season comes on, the soil moisture rises toward the surface again. On reaching the calcium carbonate resulting from the former reaction, the sodium sulphate changes back to carbonate and rises to the uppermost layers of the soil [Treitz, 1908, p. 119]. (Braun-Blanquet 1932:204)
BRAUN-BLANQUET, Josias. 1932. Plant sociology: the study of plant communities. (Trans.: George D. Fuller; Henry S. Conard) New York: McGraw-Hill Book Company.