Specific Problems of Salt-Affected Soils

Salinization, i.e. the accumulation of salts in soils, occurs when evapotranspiration exceeds precipitation. Sodium salts are of major importance, both from a quantitative and qualitative perspective. Sodicity is the accumulation of sodium which, beside other problems, causes soil destabilization and deteriorates soil hydraulic properties such as infiltration rate and hydraulic conductivity. The negative effects are caused by the dispersive character of sodium ions. Several measures of soil management help to overcome the sodicity-caused soil deterioration with calcium application being the most important one. Calcium helps to counteract dispersion by flocculation of clay particles. The most important anion of sodium salts is chloride which acts as a micronutrient of plants but at higher concentrations is toxic to many dicotyledonous species. As a monovalent anion, it is highly mobile in plants and soils. Although similarly mobile in soil as chloride, sulfate can form gypsum with calcium. Gypsiferous soils contain compacted horizons that inhibit plant growth. The oxide anions of selenium, boron, and arsenic may be toxic at higher concentrations and occur in specific soils derived from parent material rich in these anions.