Nutrients Iron: Generalities
Iron is a catalytic microelement, considered among the ten indispensable elements for plant life; among those elements, that is, that if one fails, only the plants cannot survive.
In plants it is present mainly in the leaves, accumulated mainly in chloroplasts where it participates in the synthesis of chlorophyll, the very important pigment that colors green plants and in chlorophyll photosynthesis where it transforms light energy into chemical energy. Linked as it is to chlorophyll, it soon becomes clear that in its absence all the green organs, in particular the leaves are bleached by achlorophyllia, that is to say, poor or lack of chlorophyll formation. Iron is an integral part of various enzymes (catalase, peroxidase, various cytochromes, cytochromoxidases, ferridoxine and flavoproteins): these intervene in the oxidation-reduction reactions of photosynthesis, carbohydrate metabolism, nitrate and nitrite reduction, and respiration. Furthermore, iron actively participates in the process of biological fixation of atmospheric nitrogen, also being in the active center of nitrogenase of radical nodules in non-haematic form associated with molybdenum.
The soils contain significant amounts of iron in the form Fe +++ (ferric ion), to be absorbed by the plants and subsequently translocated in the leaves it must be transformed (reduced) to the form Fe ++ (ferrous ion). In soils characterized by high pH (7.8 - 8), with a high content of active limestone, there is no reduction of the ferric ion in ferrous determining the unavailability of iron due to insolubility and therefore not useful for plant nutrition. Chlorosis is also widespread in sandy soils, in the presence of water stagnation, in soils with a low content of organic substance, in soils with the presence of microelements antagonistic to Iron (Mn, Cu, Zn, Mo) or an excess of phosphorus in the ground. Also some weather conditions, such as exceptionally cold weather, frequent sometimes at vegetative growth or shortly after and often linked to stagnation of humidity or, on the contrary, abnormally hot periods. Therefore we can say that almost never the ferric chlorosis manifests itself for a real lack of the element, but it is given by a scarce availability of the element as consequence of external factors or from chemical conditions of the ground that prevent the iron from being not assimilable.
The prevention and treatment of iron deficiencies, today, are carried out mainly using products based on iron chelates that have the characteristic of keeping the iron available even in unfavorable chemical conditions of the ground.
Iron deficiency induces in the plant a typical symptomatology called ferric chlorosis. Chlorosis (from the Greek chlorтs = yellow-green) is manifested by internervale yellowing of the leaves, with basipetal development, that is having progression from the apex (younger leaves) to the base (older leaves). In the most serious cases there is also leaf whitening, apical and marginal necrosis of the leaves up to the total weakening of the plant with little or no production.
The species that are most affected by this deficiency are: the peach tree, the actinidia, the vine, the pear tree grafted on the quince, the citrus fruits, some horticultural and flowering species such as tomatoes, lettuce, gerberas, hydrangeas and roses.