Part 1 of the Nutrients series; theme pH, EC and precipitation

The EC (electrical conductivity) is a measure of the concentration of ions (salts) in water, soil and substrate moisture. The more ions dissolved in the water, the higher the EC.

When analysing the water or substrate, it becomes clear that the measured EC is determined not only by nutritional elements but also by ballast salts (chloride and sodium). In order to make a good comparison with the target value, the measured EC will therefore first have to be converted to the EC (v), the so-called nutritional EC. The EC (v) is obtained by reducing the measured EC by 0.1 x the highest value of sodium or chloride, or standard with sodium in case chloride is used as fertilizer. The EC(v) can then be used to convert the measured nutrient content to the target EC indicated as EC(c).

The EC is not only a control tool for fertilization, but can also be used as a control agent for crop growth. Due to a high EC around the root, you can control the crop generatively, because you increase the osmotic value in the root environment, so that the plant can absorb water less easily, so that the stretching of the cells (vegetative growth) is inhibited. A low EC, on the other hand, facilitates water absorption and can lead to more root pressure, especially with little evaporation. At the same time, with a low EC, you give fewer nutritional elements, which can cause a nutritional deficiency earlier.

The EC in the substrate is not only determined by the settings on the fertilization unit, the growth rate and thus the absorption of the crop also plays an important role. Because in the summer the plant absorbs more and more water in relation to nutrients, a light reduction on the EC is often used during this period, to prevent the EC from increasing. What is often forgotten is that the EC also influences the absorption of individual elements. For example, potassium is better absorbed at a high EC and calcium is worse. This has to do with an increase in competition (antagonism) in absorption between potassium and calcium at a higher concentration, but also because the calcium absorption, unlike potassium, depends on the water absorption by the plant and this is inhibited at a high EC.

The pH is a scale to indicate acidity and determines to a large extent the solubility of the nutrients. Too high a pH can indirectly inhibit crop growth because nutrients are less easily absorbed, while too low a pH can cause problems with root quality. Phosphate and trace elements get out of so

lution at a high pH or can precipitate with other elements. Magnesium washes out faster at a low pH, causing a shortage earlier. For each of the nutrients, a specific pH range applies within which the solubility is optimal, on average for On average for all elements it is between 5.5-6.5.

Normec Groen Agro Control regularly performs analyses on clogged droppers, in which the elements iron, phosphate, zinc and calcium are often found. ”Research on pollution” is combined with organic pollution so that it becomes clear what is most present.

The pH can be controlled with the fertilization unit, often via a separate pH control. This can in any case prevent nutritional elements from precipitating in the drip hoses. If the pH has to be corrected with a lot of acid at the unit, it is advisable to acidify the water beforehand. This makes the control at the unit more stable.

In the root environment, the pH of the feed water plays a limited role, because the plant itself largely determines the pH around the roots. When cations (K+, Ca2+, Mg2+, etc) are absorbed, acid ions (H+) are excreted by the roots, causing the pH to drop, while when anions (NO3-, PO4-, SO42-) are absorbed H+ so that bicarbonate is formed in the root environment and the pH rises. The balance between the uptake of cations and anions thus determines the pH in the substrate. This balance is not always equal, but can be influenced by the growth phase and growth rate of the crop. More nitrate uptake with rapid growth results in a higher pH and a strong generative development in which more potassium is absorbed gives a lower pH. Finally, bicarbonate in the starting water can also cause the pH in the substrate to rise. A little bicarbonate (up to 0.5 mmol/l) in the drip water ensures that the pH remains more stable and cannot sink at night under the influence of microbiological processes. Our laboratory reports the bicarbonate content based on the total acid buffering effect of the water. This not only looks at the buffer effect of bicarbonate, but also at that of other elements, such as phosphate. This creates a more reliable picture of what the influence of the bicarbonate is on the pH and exactly how much acid is needed to lower the pH to the desired level.