Osmotic pressure in turn affects the ability of plants to absorb water through their roots. Plants can absorb water readily when osmotic pressure is low, but absorption becomes more difficult as the pressure increases. Even if the soil is thoroughly wet, plant roots have difficulty absorbing water when the osmotic pressure is high. When the pressure is unusually high, it may even be impossible for plants to absorb sufficient water for normal plant growth. Under these conditions, plants may actually wilt when the roots are in water.
Salts break down into ions when they go into solution.
The various anions and cations produced when the salts are dissolved in water exert considerably different effects on plants. Calcium carbonate is considered slightly soluble, while calcium sulfate is moderately soluble. Waters from areas where gypsum is prominent are almost always high in calcium sulfate. Examples of areas where this condition occurs are the Pecos Valley, the Tularosa Basin, and at locations in the Estancia Valley. Waters high in calcium or magnesium are considered hard and are not desirable for domestic water supplies, but hard water is considered good for irrigation.