Carbonates & bicarbonates hazard of irrigation water
Bicarbonate hazard of irrigation water
High carbonate (CO3=) and bicarbonate (HCO3-) increases SAR index (around >3-4mEq/L or >180-240mg/L). Let's explain why:
The concentration of Ca and Mg decreases relative to sodium and the SAR index will be bigger. This will cause an alkalizing effect and increase the PH. Therefore when a water analysis indicates high PH level, it may be a sign of a high content of carbonate and bicarbonates ions.
The RSC has the following equation:
It is another alternative measure of the sodium content in relation with Mg and Ca. This value may appear in some water quality reports although it is not frequently used.
If the RSC < 1.25 the water is considered safe
If the RSC > 2.5 the water is not appropriate for irrigation.
Some practices to solve problem of carbonates and bicarbonates in irrigation water
- Injection of sulfuric acid to dissociate the bicarbonate ions (PH around 6.2) giving off carbon dioxide. It allows the calcium and magnesium to stay in solution in relation with the sodium content.
- Add gypsum when soils have low free calcium plus leaching.
- Add sulfur to soils with high lime content plus leaching