pH is a logarithmic measure of the concentration of H⁺ ions in a solution: pH = − log [H⁺]
This means that a difference of 1 pH unit corresponds to a factor of 10, while a difference of 2 pH units corresponds to a factor of 100.
Example: A solution at pH 4 therefore contains 100 times more H⁺ than a solution at pH 6, in other words, it is 100 times more acidic.
This is why pH should never be considered a secondary parameter in fertigation management.
For most crops, excluding acidophil plants, the following ranges can be used as reference values for the irrigation solution:
- Optimal range: pH 5.3–6.3
- Acceptable range: pH 5.0–6.6
- Risk zone: < 4.9 or > 6.7
- pH < 4.0 or > 8.0: significant risk of plant damage and major disruption of nutrient uptake
Why is regular monitoring so important?
An abnormally low pH does not only cause a temporary nutritional imbalance. Excessive acidity around the roots can damage root tissues and root hairs, with effects that may persist even after the pH has been corrected.
The safety of the fertigation system is therefore essential.
A modern fertigation unit should ideally be equipped with two pH sensors, allowing continuous cross-checking of the measurements. In the event of an abnormal reading or a significant discrepancy between the two sensors, the system should have a high-priority alarm capable of stopping irrigation, rather than allowing a potentially harmful solution to be supplied to the plants for several irrigation cycles.
These sensors should also be calibrated regularly, ideally once a week, using suitable buffer solutions.
Finally, even with a fully automated system, an independent pH meter remains an excellent field-control tool for carrying out daily manual measurements of both the irrigation solution pH and the drainage pH.
Modern fertirrigaion unit (on the left) and Wireless substrate monitoring probe (on the right)
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