Chapter 15

Water Quality for Irrigating Vineyards

Sodium Hazard

While ECw is an assessment of all soluble salts, sodium hazard is defined separately because of sodium’s specific detrimental effects on soil physical properties—structure and permeability―in a vineyard. Damage arises as sodium displaces calcium and magnesium from soil colloids, causing them to disperse and lose structure.

Measuring and Classifying the Sodium Hazard

The sodium hazard is typically expressed as the sodium adsorption ratio (SAR). The sodium adsorption ratio relates the concentration of sodium to the concentration of calcium and magnesium (See equation below).

Adjusted Sodium Adsorption Ratio

The adjusted sodium adsorption ratio (sometimes symbolized as adj SAR) is a modification of the original SAR calculation. It serves the same purposes, but is modified to include the effects of bicarbonates and carbonates, in addition to calcium and magnesium.

Managing Irrigation Water High in Sodium

Water infiltration problems due to low salt content or high SAR can be improved by injecting calcium into the water. Calcium injection reduces sodium hazard by reducing water SAR, and increasing water EC. Calcium also prevents the formation of sodium bicarbonate (an additional water infiltration hazard).

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