Soil salinization

DEFINITION: Process in which water-soluble salts build up in soil within the root zone of plants

The salinization of soil on agricultural lands can result in poor plant growth and reduced crop yields, and attempts to reduce salinity through increased irrigation can lead to contamination of water supplies.

In the process of soil salinization, water-soluble salts build up in the part of the soil known as the root zone, where the soil comes into contact with the roots of plants, blocking the movement of water and nutrients into plant tissues. Soil salinization rarely occurs naturally. Rainwater is virtually free of dissolved solids, but surface waters and groundwater contain significant quantities of dissolved solids, ultimately produced by the weathering of rocks. Evaporation of water at the land surface results in an increase in dissolved solids in soil that may adversely affect the ability of plant roots to absorb water and nutrients.

In arid regions, evaporation of soil water potentially exceeds rainfall. Shallow wetting of the soil followed by surface evaporation lifts the available dissolved solids to near the surface of the soil. The near-surface soil, therefore, becomes richer in soluble salts. In natural arid areas, soluble salts in the subsurface are limited in quantity because rock weathering is an extremely slow process, and degrees of soil salinization detrimental to plants are uncommon.

The irrigation of arid-climate soils with surface water or groundwater provides a constant new supply of soluble salt. As the irrigation water evaporates and moves through plants to the atmosphere, the dissolved solid content of the soil water increases. Eventually, the increase in soil salt will inhibit or stop plant growth. It is therefore necessary to apply much more water to fields in arid climates than the amount required for plant growth, so that the water flushes salts away from the plant root zone. If the excess water drains easily to the groundwater zone, however, the groundwater becomes enriched in dissolved solids, which may be detrimental.

If the groundwater table is near the surface, or if impermeable soil zones are close to the surface, over-irrigation will not alleviate the problem of soil salinization. Alleviation of this condition requires the installation of subsurface drains to carry the excess soil water and salts to a surface outlet. The problem with this method is that disposing of the salty drain water is difficult. If the drain water is released into surface streams, it degrades the quality of the stream water, adversely affecting downstream users. If the water is discharged into evaporation ponds, it has the potential to seep into the groundwater zone or produce a dangerously contaminated body of surface water, as occurred at the Kesterson National Wildlife Refuge in California, where concentrations of the trace element selenium rose to levels that interfered with the reproduction of resident birds.

Bibliography

Bandak, Soraya, et al. "A Longitudinal Analysis of Soil Salinity Changes Using Remotely Sensed Imageries." Scientific Reports, vol. 14, no. 10383, 6 May 2024, doi.org/10.1038/s41598-024-60033-6. Accessed 18 Sept. 2025.

Blanco, Humberto, and Rattan Lal. Principles of Soil Conservation and Management. Springer, 2008.

Shokri, Nima, et al. “Soil Salinization: A Rising Threat to Ecosystems and Global Food Security.” Eos.org, 21 Oct. 2024, eos.org/editors-vox/soil-salinization-a-rising-threat-to-ecosystems-and-global-food-security. Accessed 18 Sept. 2025.

Vengosh, A. “Salinization and Saline Environments.” In Environmental Geochemistry, edited by Barbara Sherwood Lollar. Elsevier, 2005.