Effects of Salts on Soils and Plants

Sodic (black alkali) soils are a particularly difficult management problem. The water permeability of these soils to water is very slow. The pH of sodic soils is commonly greater than 9 or 9,5, and the clay and organic fractions are dispersed. Dispersed organic matter accumulates at the surface of poorly drained areas as water evaporates and imparts a black color to the surface, hence the name black alkali. Sodic soils are found in many parts of the western United States. In some locations they occur in small patches, slick spots, less than 0.5 ha in extent. Such patches occupy slight depressions, which become accentuated as surface soil particles disperse and are blown away by wind erosion. The percolation of insufficient water to satisfy plants and to control salinity is the main problem associated with sodic soils. In addition, their relatively low soluble-salt concentrations and high pH values can result in direct Na toxicities to the most sensitive plants. 

The relative growth of plants in the presence of salinity has been termed their salt tolerance. Earlier data were summarized by separating plants into several salt-tolerant groups. Subsequent listings were in terms of relative plant growth at various salinity levels (EC) of the soil s saturation extract (Table 11.2). Some recent listings 

Tall wheatgrass (Agropyron elongation (Host) Beauv.) 11 15 18 

Crested wheatgrass (Agropyron desertonm (Fisch. ex Link) Schult.) 6 11 18 

Narrow-leaf birdsfoot trefoil (Lotus temiifolius CL.) Reich) 6 8 10 

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