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Why can highly salty soil make it difficult for plants to grow?

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Cluster of translucent, white salt crystals with sharp cubic shapes viewed under a microscope at high magnification against a dark background. — salt Salt crystal magnified.

Highly salty soil inhibits plant growth primarily by disrupting the plant's ability to absorb water and nutrients. Under normal conditions, water moves into plant roots through osmosis. However, when the concentration of salt in the soil is too high, it creates an osmotic imbalance that can cause water to flow out of the roots and back into the soil, leading to dehydration.1

Furthermore, as the salt concentration in the soil increases, the energy required for a plant to extract water rises, making it increasingly difficult for the plant to obtain the moisture it needs to survive. In addition to these water-uptake issues, excess salinity can cause a lack of nitrogen uptake and, in some cases, the dissolved salts can be directly toxic to the plant when absorbed through the roots.21

Beyond these physiological effects, high levels of sodium can alter the physical structure of the soil, making it sticky when wet and hard when dry, which can render the soil nearly impervious to both water and root penetration.2