Saline, Sodic, and Saline-Sodic Soils
Saline Soils
All soils contain some water-soluble salts, but when these salts occur in amounts that are harmful to seed germination and plant growth, they are called saline. Salt-affected soils are most common in arid and semiarid regions where evaporation exceeds precipitation and dissolved salts are left behind to accumulate, or in areas where vegetation or irrigation changes have caused salts to leach and accumulate in low-lying places (saline seeps).
Salinity Effects on Soil Physical Properties
Although excessive salts can be hazardous to plant growth, low to moderate salinity may actually improve some soil physical conditions. Calcium and magnesium ions have a tendency to “flocculate” (clump together) soil colloids (fine clay and organic matter particles), thus, increasing aggregation and macroporosity. In turn, soil porosity, structural stability and water movement may actually be improved in saline soils.
Salinity Effects on Plant Growth
The primary effect of excessive soluble salts on plants is to limit the ability of plant roots to absorb soil water even under wet soil conditions. Soil water flows from higher osmotic potential (low salt concentration) to lower osmotic potential (high salt concentration). A soil solution with low osmotic potential due to the higher concentration of soluble salts compared to the plant cells, will not allow plant roots to extract water from soil, causing drought-like symptoms in the plants. This is referred to as the osmotic or water-deficit effect of salinity. Effects of soil salinity are manifested in loss of stand, reduced plant growth, reduced yields, and, in severe cases, crop failure.
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