Soil and Water Salinity

Definitions and forms of salinity All natural waters contain soluble salts. The concentration of the salts determines whether the water is of high quality (drinkable or usable for irrigation without need for special precautions) or of low quality (brackish or saline). Water in the soil also contains soluble salts (sometimes called free or nonattached salts). The amount of salts in the root zone (or the salt concentration in the soil solution) determines whether the soil is “normal” or “salt-affected” (saline, sodic, or salinesodic). Salinity becomes a concern when an “excessive” amount or concentration of soluble salts occurs in the soil, either naturally or as a result of mismanaged irrigation water. Worldwide, salt-affected soils are most abundant in arid regions, and in irrigated lands the formation of salt-affected soils is the most important process of chemical soil degradation. In Hawaii, salinity is more of a concern in irrigated shoreline areas where groundwater supplies are influenced by intrusion of sea water. Sediments dredged from salt-laden deposits are also chronic problems, particularly when used as fill on which vegetation is attempted. In Hawaii, salinity is generally a cyclical problem related to water availability from rainfall; it is aggravated in dry years and relieved in wet years. Fortunately, most of Hawaii’s soils have physical and structural qualities that impart behavioral resilience and prevent salts from imposing irreversible soil degradation. The most common salts in water and soil solutions are composed of the cations sodium (Na), potassium Chapter 17