why can’t we use salt water for irrigation?
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The answers so far have not explained why salt is bad for plants. Too much salt makes it impossible for plant roots to absorb water.
Water has a tendency to move from areas with low concentrations of dissolved stuff or solute (such as salt, sugars and other molecules), to areas of high solute concentration. Plants normally take advantage of this to absorb water from the soil. The root cells have higher solute concentrations than the surrounding soil. The membrane around the cell lets water pass through but controlls how much salt passes through. This means water moves from the surrounding soil into the roots. If you irrigate with salt water, the water in the soil will eventually have a higher solute concentration than the plant roots can maintain and water will tend to move out of the plant.
Some plants have adaptations that let them keep higher solute concentrations in their roots, so they can absorb water from salty soil.
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