In the steppes and deserts, evaporation on the average greatly exceeds precipitation and there are many topographic depressions that have no outlet to external drainage systems. Here the products of rock weathering are brought by intermittent flowing streams in times of flood and left behind on the basin floor. Along with clay, silt and sand are the dissolved mineral salts that crystallize out as the water evaporates.
Shallow lake basins, or playas, of extreme flatness are often covered with only a thin film of water, which evaporates rapidly, leaving its salts on the surface. Most persons are familiar with the salt flats of Great Salt Lake in Utah, on which so many automobile speed records have been set. Salts found in the various playa lakes of the southwestern United States are soda (Na2CO3), borax (Na2B4O7), calcium carbonate (CaCO3). Where salts are thick and pure in the inner parts of the playas there is no soil in the true sense of the word. The term halomorphic soil is properly applied to marginal areas where silts and clays make up a large proportion of the body of the soil.
The pedogenic process in the development of halomorphic soils is salinization. Two major groups of halomorphic soils are recognized: saline soils (solonchak) and alkali soils (solonetz). Halomorphic soils are classed as intrazonal because of their poor drainage and limited extent.
Saline soils (solonchak, or white alkali soils) contain chlorides, sulphates, carbonates, and bicarbonates of sodium, calcium, magnesium, and potassium. These soils arc light coloured and show poorly developed horizons. Although there are many species of plants adapted to saline soils the plant cover is at best sparse. Plants, which are salt-tolerant, are known as halophytic plants. They include grasses, shrubs, and some trees. Agriculture is not possible on saline soils unless they are flushed out with large quantities of irrigation water to remove the salts. This has been done to advantage to reclaim much good agricultural land in the southwestern United States.
In the second major group of halomorphic soils, the alkali soils (solonetz or black alkali soils), sodium salts predominate, especially sodium carbonate (NaCO3). The soil profile is characterized by the presence of a dark, hard, columnar layer, i.e., a layer with prismatic structure. Although salts of the alkali soils are of somewhat different chemical properties from salts of the saline soils, both soils occur in the same areas. Alkali soils occupy areas of somewhat better drainage than the saline soils may be derived from the latter by the removal of more soluble salts (desalinization). Grass and shrub vegetation is found on alkali soils, but the species are particularly alkali-resistant.
With improved drainage-whether by man's intervention or by natural processes-solonetz is transformed by leaching of salts, into soloth, a surface layer and a heavy-textured, dark brown B-horizon with columnar structure.
"The world is a book, and those who do not travel read only a page", St. Augustine said. Here at www.travel-university.org we believe that every page must be read and explored. Travel is an avenue of learning that no text or classroom can teach. The world is a living classroom and you the student. We invite you to the www.travel-university.org library where you can read general interest and detail oriented articles.
