Soil salinity is caused by several factors. Soils may become saline as a result of land use, including the use of irrigation water with high levels of salt. Seawater is also a source of salts in low-lying areas along the coast through tidal estuaries or when rainfall in coastal regions mixes with sea spray. Saltwater intrusion into freshwater aquifers may occur when wells are close to the coast and water is pumped to the surface for various purposes, including irrigation. Irrigating from salt-impacted wells or saline industrial water may lead to the formation of saline soils.
Soil sodicity, on the other hand, is caused by high sodium levels in soils at concentrations greater than 15 percent of the cation exchange capacity. Sodic soils tend to have poor structure with unfavorable physical properties such as poor water infiltration and air exchange, which can reduce plant growth.