Sodium in irrigation water will affect the productivity of your primary production enterprise.
Sodicity is the concentration of Sodium (Na+) ions in the water. The balance of sodium ions relative to calcium and magnesium ions is called the sodium adsorption ratio.
Areas in Australia adversely affected by sodicity and acidity are much more extensive than the areas adversely affected by salinity. Sodicity and acidity affect 23% and 4.5% of agricultural land respectively. Sodicity is largely naturally occurring and the condition can be corrected by gypsum.
There is a classic test for sodicity in soils- take a handful of soil in a jar and add water. Stir and allow to settle. The turbidity (cloudiness) of the water indicates the level of sodicity (from Jar one on the left -low turbidity, to jar three - high turbidity). The turbidity does not generally settle out of the water. By placing a white spatula in your jar, visibility of sodicity is easier.
High Sodium Adsorption Ratio (SAR) levels in water cause poor water penetration through the soil, poor drainage and low aeration levels in the soil. Soils often develop a hard, blocky structure and become crusted at the surface.
There are a number of general guidlines for using sodic water:
- Low sodicity water (SAR<3) can be used for irrigation on most soil types with little risk of aggravating a soil sodicity problem.
- Medium sodicity water (SAR 3-12) may cause problems in both sodic and non-sodic clay soils but can be used on coarse textured soils ands and loams) and organic soils. Applications of gypsum promote the leaching of sodium in clay soils.
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High sodicity water (SAR>12)is unsuitable for irrigation except if you have medium salinity levels. However, the salinity level needed to counteract the sodicity would badly affect crop yield in most crops and pasture species. Adding gypsum to the water can reduce the impact of the high concentration of sodium.
