General concepts: pH

pH is a variable factor of between 0 and 14 that indicates the acidity or the alkaline levels of a solution. The substances capable of allowing hydroxide groups (H) are acidic and those capable of allowing hydroxyl (OH) are basic or alkaline.

The importance of pH in crops

The pH of the nutrient solution can affect vegetable growth in two main ways:

1. It can affect the availability of nutrients, given that, with extreme values of pH there is precipitation of certain nutrients remaining in a form that is not suitable for the plants.

2. The capacity of the roots to absorb nutrients. All vegetable species present certain features of pH in which its absorption is ideal, outside this range, radicular absorption becomes difficult. If the imbalance is extreme, the radicular system may deteriorate or toxins may be produced.

The pH in the irrigation system

The pH in fertirrigation solutions, as well as in earth crops like in hydroponie, should be such that it allows all the nutrients to be dissolved without damaging the roots, in this way avoiding the formation of precipitates which could cause stopping in the irrigation systems and prevention of radicular absorption of these nutrients.

The ideal amount of pH is between 5.0 - 6.5 given that the plant assimilates practically all the nutrients. For amounts above pH 6.5 the formation of precipitates can cause serious problems. Below pH 5 can see the deterioration of the radicule system, above all in hydroponical crops.

pH in the ground
The vast majority of irrigation water which we control shows a pH level above the maximum, the quantity of acid to be used depends mainly on the concentration of bicarbonate ion present in the irrigation water, given that this acts as a control against changes in pH in the irrigation water and in elevated concentrations it is necessary to have a higher level of acid for the neutralisation and adjustment of the pH.

pH adjustment
The most generalised case is that the irrigation waters have pH levels superior to 5.8 and normally the presence of bicarbonate ions with a reduced amount of carbonate ions, which are responsible for this. The way of reducing the pH in these irrigation waters consists of eliminating these ions, and this is achieved by the addition of some acid. The neutralisation reaction is the following:



Bicarbonato:










Carbonato:









The acids, which are used most in nutritive solutions for crops inside greenhouses, are nitric acid and phosphoric acid. These acids have the advantage that in addition to helping to adjust the pH, they provide nutritive elements, which are necessary for the plant.