Role of calcium in plants
Calcium (Ca) is an alkaline-earth metal and is the fifth most common element on the earth’s crust (about 3%).
In soils, calcium is always found in the combined form in the form of carbonate, phosphate, silicate and in organic matter, combining with other nutrients, reducing the solubility both in itself and in the other element.
The role of calcium in plants and in the soil-plant system is not just nutritious. Calcium acts on the pH and exerts a “flocculant” action on colloidal micelles of humus and clay, contributing to the improvement of the soil structure. The action is carried out as calcium carbonate (CaCO3) contributing to the creation of a soil structure more suitable for nourishment and root development.
Calcium becomes part of the proto pectine, where it is a fundamental element, constituting the cell wall. For this reason it is responsible for the mechanical resistance of the tissues and the cellular turgidity, prolonging also the maturation times and the senescence of the fruits, keeping intact the structure of the walls and cell membranes.
For this reason calcium acts in improving the general vigor of the plant, the consistency of the stems and influences the assimilation of other nutrients, also neutralizing some toxic substances that are produced in the plant.
Among other functions, the presence of calcium in plants induces the production of salicylic acid, which promotes all those reactions that help the plant to defend itself against external attacks.
Calcium, therefore, by controlling the synthesis of salicylic acid, plays the role of activating cell health, directing incoming information and helping the defense ability of plants against various dangers, such as pathogen attacks. A defensive action typical of the production of salicylic acid is to cause death (necrosis) of the cells around a wound or tear to avoid infection of the whole plant.
Ordinarily, calcium is present in the soil in sufficient quantities for all the physiological needs of the plants. On the other hand, the excess of this element in the soil is more problematic, as it determines, beyond certain levels, the insolubility of phosphorus (retrogradation) and other microelements, causing the so-called “ferric chlorosis”, which is an iron deficiency in the tissues. plants, not so much and only due to the lack of iron in the soil but to an immobilization of the iron in the soil caused by the calcium-based compounds.
This phenomenon is more evident in so-called acidophilous plants, which tolerate the presence of this element in extremely low quantities.
For this reason the calcium inputs to the soil must always be justified by real and proven (with chemical analysis) deficiencies. Its contribution may be necessary in excessively acidic soils (where it corrects the pH towards neutrality) or for plant crops that have specific needs for this element. However, the contributions should be carefully evaluated because, if it is easy to enrich the soil in calcium, it is complicated then, in case of excess of intake, to eliminate it from the ground.
As calcium is present in some chemical fertilizers, especially those containing nitrogen, phosphorus and potassium, often involuntary excesses of this element are created with secondary consequences of difficult solution. Among the fertilizers that are based on calcium we remember: calcium nitrate, calcium cyanamide, mineral superphosphate, Thomas slag. The soil improvers that instead bring calcium to correct the acidity of the soils are based on: calcium carbonate coming from limestone, marl, dolomite: agricultural lime alive and off.