How to interpret water analysis for irrigation

How to interpret water analysis for irrigation

The reading of an analysis of water for irrigation and therefore of its bulletin is an activity that needs particular professional skills (belonging to the Agronomists and Forest Doctors) and that allows us to understand, sometimes in a preventive way, the suitability for use of that water and compatibility with crops and soil.
The following is a bulletin of analysis, to understand how to interpret water analysis for irrigation, with some of the most important determinations in order to understand the most salient features of the water. In this case the following parameters and values ​​were determined: pH, Electrical Conductivity, calcium ions, sodium, magnesium, chlorides and sulfates as well as the Total Hardness and Sodium Adsorption Ratio (SAR “Sodium Adsorpion Ratio”). More details or investigations can determine other parameters that may concern potassium, other elements and microelements or parameters that help us to understand possible characteristics of our waters for irrigation.

In the case of our bulletin we are in the presence of water with subacid pH, with an electrical conductivity in μS of 1,897; this value gives an indication of the electrical conductivity of the water which in turn is linked to the salts dissolved therein. Water for irrigation should never exceed the indicative value of 800 μS but this parameter can fluctuate greatly depending on the quality of dissolved salts. Sodium (Na) plays a fundamental role among dissolved ions. Waters with high contents of this ion are absolutely unadvisable for irrigation use; in this case our bulletin is already quite high; take into account that the high sodium presence has two negative actions: with regard to the absorption of the elements (and microelements) in the plants with induced chlorosis determination and with regard to the soil with deconstruction of the same; consider that many of the landslide phenomena of our soils diagnosed are due to the high contributions of this element both with water and with fertilizers and pesticides. Ioni Calcium and Magnesium and the chlorides and sulphates, if not present in high concentrations, are however interesting in their ratio by characterizing the qualities and characteristics of the water in relation to the soil and the absorption of the elements.
Finally, a special mention should be given to the SAR, which is a function relationship between three elements (Ca, Mg and Na), which gives us a very immediate indication of the ability of soils to absorb Sodium with respect to calcium and magnesium. SAR values ​​below the unit characterize waters with a better balance of the three elements with respect to the soil’s absorption capacity; increasing SAR value indicates a danger of water to “release” sodium in the soil with all the negative phenomena we have mentioned.
In the bulletin in question a further classification is made (EC-S), which relates the Electrical Conductivity with the SAR and that classifies the characteristic to the irrigation of our water.
As usual, the fundamental thing of analysis reports is that they show a minimum classification of the same in addition to the main quantitative and qualitative parameters.

Guido Bissanti

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