Sodium Hazard Irrigation water containing large amounts of sodium is of special concern due to sodium's effects on the soil and poses a sodium hazard . Sodium hazard is usually expressed in terms of SAR or the sodium adsorption ratio. SAR is calculated from the ratio of sodium to calcium and magnesium. The latter two ions are important since they tend to counter the effects of sodium. Continued use of water having a high SAR leads to a breakdown in the physical structure of the soil.
Sodium is adsorbed and becomes attached to soil particles.
The soil then becomes hard and compact when dry and increasingly impervious to water penetration. Fine textured soils, especially those high in clay, are most subject to this action. Certain amendments may be required to maintain soils under high SARs. Calcium and magnesium, if present in the soil in large enough quantities, will counter the effects of the sodium and help maintain good soil properties. A water with a SSP greater than 60 percent may result in sodium accumulations that will cause a breakdown in the soil's physical properties.