Soil salinization
Soil salinization is a process where water-soluble salts accumulate in the soil, particularly within the root zone of plants, negatively impacting plant growth and agricultural productivity. This condition often arises in arid regions where evaporation rates exceed rainfall, causing salts to rise to the surface as water evaporates. While natural occurrences of soil salinization are rare, human activities such as irrigation can exacerbate the issue by introducing additional soluble salts into the soil. Increased irrigation may seem like a solution; however, it can lead to water contamination and further salinization if excess water is not managed properly.
Efforts to mitigate soil salinity include applying more water to leach out salts from the root zone. However, this can lead to high salt concentrations in groundwater, which poses risks for both agricultural and environmental health. When excessive irrigation is used without effective drainage, it can hinder plant growth and degrade water quality in nearby streams and ecosystems. Addressing soil salinization requires comprehensive management strategies, such as installing subsurface drainage systems, though these solutions must also consider the long-term effects on surrounding water bodies. Understanding the delicate balance of water and salt in soil is crucial for sustaining agricultural practices, especially in vulnerable arid regions.
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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 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 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 or groundwater provides a constant new supply of soluble salt. As the 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, overirrigation 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 23 July 2024.
Blanco, Humberto, and Rattan Lal. Principles of Soil Conservation and Management. New York: Springer, 2008.
Vengosh, A. “Salinization and Saline Environments.” In Environmental Geochemistry, edited by Barbara Sherwood Lollar. Oxford: Elsevier, 2005.