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How do irrigation and fertilization cause soil salinity?

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A row of cattle with brown and black coats eat feed from a long trough in a South African feedlot, separated by wooden fencing. — Feed Feedlot cattle eating grain in an intensive animal farm in South Africa.

In the context of agriculture, soil salinity occurs when salts accumulate in the soil profile to levels that inhibit plant growth. This process is primarily driven by the following mechanisms:12

Irrigation: All irrigation water contains dissolved salts. As plants absorb water through their roots, they typically exclude these salts. When the remaining water evaporates from the soil surface or is lost through transpiration, the salts are left behind. In arid regions where precipitation is insufficient to flush these salts downward through the soil, they accumulate over time.234
Fertilization: The use of fertilizers contributes to salinity by concentrating salts in the soil. Furthermore, the application of fertilizers—particularly nitrogen-based ones—can lead to the leaching of excess nutrients into groundwater, which may then be drawn back up into the soil profile through capillary action, further exacerbating salt buildup.42

If not managed through proper drainage and leaching with nonsaline water, this accumulation creates osmotic stress, preventing plants from absorbing water and potentially leading to soil toxicity.124