Saline Soils

soils with a high (more than 0.25 percent) content of mineral salts readily dissolvable in water. They are found chiefly in the southern arid regions of many countries (among them Pakistan, India, China, and Egypt), frequently in spots among nonsaline soils. In the USSR, saline soils cover an area of 52.3 million hectares (ha), or about 2.4 percent of all the soils in the country; they occur in the southern Ukrainian SSR, the Volga Region, Middle Asia (about half of all the plowed land is saline), and elsewhere. They contain mainly sulfates (sodium, calcium, and magnesium), chlorides (sodium, calcium, and magnesium), and carbonates (sodium in two forms: sodium carbonate, or normal soda; and sodium bicarbonate, or baking soda). Sometimes sodium and calcium nitrates are found in saline soils. Saline soils are classified into solonchaks (1–3 percent salts or more), solonchakovy (less saline), and solonchakovaty (saline below the plowed layer), according to the amount of salts and the nature of their distribution in the soil horizons. The degree of salinity is determined by adding up the toxic salts bound to chlorine and sulfate ions. Solonetzic soils differ from saline ones in that they contain absorbed sodium: sometimes solonetzicness is combined with salinity. Sodium salts are usually more toxic. Besides being toxic, readily soluble salts increase the osmotic pressure of the soil solution and create so-called physiological dryness, whereby the plants suffer as much as they do from soil drought. An excess of water-soluble salts results in sparseness of vegetation and the appearance of an unusual group of wild plant species, the so-called saltworts, or halophytes, which are adapted to life on saline soils.

Saline soils are formed by the accumulation of salts in soil and groundwater and by the inundation of land with marine saltwater. An arid climate and an impeded outflow of surface and subsoil water are essential factors in the accumulation of salts on dry land and in the salinization of soils. Irrigated lands frequently experience so-called secondary salinization, when many salts appear in the subsoil or groundwater. The irrigation of undrained plains raises the salty groundwater level, producing saline soils. The correct management of agriculture can prevent the unfortunate tendency toward salinization by changing its natural direction. This is achieved by flushing with both an artificial outflow of groundwater and drainage water. Saline soils are best flushed in the fall or winter because evaporation, which encourages salts to return, is reduced at these times.