Saline and Sodic Soils

Abstract

According to different estimates, there are 831 to 932 million hectares of salt affected soils – saline soils, saline-sodic soils and sodic soils. The measure of salinity is the electrical conductivity of the saturation extract (ECe) and the measure of sodicity is the exchangeable sodium percentage (ESP) or the sodium adsorption ratio (SAR). Saline soils have ECe > 4 dS m−1 (decisiemens per meter) at 25° C and ESP 15 (low soluble salts and high exchangeable Na+). Saline-sodic soils are characterized by ECe > 4 dS m−1 and ESP > 15 (both salts and exchangeable sodium are high). These soils mainly occur in arid and semi-arid regions where precipitation to evapotranspiration ratio is low. These soils also develop in coastal regions because of the flooding of sea water, and in irrigated areas due to the rise of the groundwater table and in some impermeable soils of the humid regions due to lack of leaching. Salts adversely affect plant growth and crop yield. Crop failures are common occurrences although some plants may have some degree of tolerances. Salt tolerant crops can be grown in some low to moderately saline soils, but soil salinity may be so severe in some cases that cropping becomes impossible. Management of saline soils involves selecting salt tolerant crops, salt scraping, salt flushing, and leaching with irrigation and artificial drainage. Usually, chemical amendments are not necessary for the reclamation of saline soils, but chemical treatment is needed prior to leaching for managing sodic soils. Substances that contain soluble calcium such as gypsum and CaCl2, and sulfuric acid or substances that produce sulfuric acid after application to soil such as sulfur, pyrite, ferrous sulfate, aluminium sulfate etc. are used as amendments for sodic soils. Phytoremediation of sodic soils has also been successful on some occasions.