The pH indicates the amount of hydrogen bonds in a solution. Its value is between 0 (acid) and 14 (basic), being 7 pH neutral.
The pH is the negative logarithm in base 10 of the activity of hydrogen ions:
pH=-log10[aH+]
Importance of pH in crops
The pH of the nutrient solution can affect plant growth in two main ways:
- The availability of nutrients, since with the extreme values of pH the precipitation of certain nutrients occurs, remaining in a form not available to plants.
- To the capacity of absorption of nutrients by the roots. All the vegetal species present characteristic characteristics of pH in which their absorption is ideal, outside this range, the root absorption is hindered. If the deviation is extreme, the root system may be damaged or toxicities may occur.
In the following graph we can observe the solubility of the main elements against pH:
Troug diagram
The pH in the fertigation solution
The pH in the fertirrigation solutions, both in soil culture and in hydroponics, must be such that it allows to be dissolved in all the nutrients without damaging the roots, avoiding This way the formation of precipitates that could cause clogging in the irrigation systems and unavailability for the root absorption of said nutrients.
The ideal pH range is between 5.0 and 6.5, since practically all of the nutrients are assimilable by the plant. Above pH 6.5 the formation of precipitates can cause important problems. Below pH5, the root system may deteriorate, especially in hydroponic crops.
The pH in the soil
The vast majority of the irrigation waters that we manage show a pH above optimum, the amount of acid to contribute depends mainly on the concentration of the bicarbonate ion present in the irrigation water , since it acts as a buffer against pH changes in irrigation water and at high concentrations, a greater amount of acid is necessary for its neutralization and pH adjustment.
pH adjustment
The most common case is that irrigation waters have a pH above 5.8 and normally the presence of bicarbonate ions, and somewhat less carbonate ions, are responsible for this . The way to lower pH of this irrigation water is to eliminate these ions, and this is achieved with the addition of some acid.
The most commonly used acids in nutrient solutions for soilless crops are nitric acid and phosphoric acid. These acids have the advantage that in addition to serving to make the pH adjustment, they provide necessary nutrients for the plant.
Our machines are connected in by-pass in the irrigation head, collecting water after the filtering system adding the fertilizers and acid and injecting everything upstream of the filtering system , being responsible for making a homogeneous mixture. Simultaneously they measure the pH value of the mixture, making a continuous adjustment in the doses, resulting in a stable and desired pH value.
