Greenhouse Management: What are pH and EC?
Isabelle Gagné: Your soil’s pH is the measure of its alkalinity (basicity) or its acidity. An acidic soil has a lot of hydrogen ions (H+), while a basic soil will have a lot of hydroxide ions (OH-). On a pH scale of 0 to 14, 7 represents neutrality (same amount of H+ and OH- ions). Under 7, the pH is acidic and above, it’s alkaline. Each crop has an optimal range, but most of the time the target pH Is between 5.4 and 6.2. It’s important to know that the soil’s pH works according to a logarithmic scale. This means that when a pH measurement varies by one unit, the acidity/alkalinity is 10 times higher/lower. That is the reason why even slight variations in pH can have a huge impact on production.
On the other hand, electrical conductivity (EC) is the measurement of all the soluble ions that are present in a soil. In other words, it measures the quantity of nutrients, which are dissolved charged ions, in the growing media.
GM: Why are pH and EC important to crops?
IG: Plants are very sensitive to pH changes as the acidity of the soil influences the solubility of nutrients. Nutrients can be present in a substrate, but they may not be available to the plant if the pH is not at the right level. As you can see in the image below, for most crops the optimal pH is 5.5-6.0 as it allows maximum nutrient availability in a growing media. Although certain species have particular pH preferences and tolerances, a range of 5.4 to 6.2 is appropriate for the large majority of crops.
This is why the EC is also important. You can view it as a snapshot of the nutrients that are currently available in your growing media. EC measurements can be done easily and regularly. However, you want to make sure you are making informed decisions through reliable data, therefore we recommend you calibrate your equipment frequently and establish a standardized testing methodology. Sending samples to an external laboratory will allow you to confirm that your calibration is adequate.
“You can view it (EC) as a snapshot of the nutrients that are currently available in your growing media ... measurements can be done easily and regularly.” — Isabell Gagné
GM: How can I manage pH and EC?
IG: Three things can influence the pH and the EC of a crop: water alkalinity, fertilizers and the plants themselves. Therefore, to manage both pH and EC properly, you will have to pay careful attention to these three factors.
It is important to know that when we talk about the alkalinity of the irrigation water, we are actually talking about the buffering capacity of the water, or its capacity to resist acidification. Irrigation water quality plays an important role in regulating the substrate’s pH and EC.