If you look in the dictionary, you will see that iron (Fe) is a micronutrient, i.e. crops need less of it compared to macronutrients, whether primary or secondary.
But as they say, it is not the quantity that matters but the quality. So it can be said that iron is essential for the health and proper development of plants because, despite being a micronutrient, it is an essential element of vital importance for the nutrition of any plant.
The presence of iron in the soil is not determined by the quantity; it has been described that iron accounts for 5% of the weight of the earth’s crust.
The solubility of iron in soil is extremely low compared to the total iron content. The uptake and its availability for crops depends mainly on the pH of the soil.
Functions of Iron
- Iron performs key functions in the processes involved in photosynthesis. It is a cofactor for more than 100 enzymes that catalyse unique biochemical reactions in processes such as photosynthesis and respiration.
- It maintains the chloroplast structure and enzyme activity.
- It is a constituent of several enzymes and some pigments.
- It helps reduce nitrates and sulphates and aids in energy production within the plant.
- It has a redox capacity, which means it can give up and gain an electron. This makes it essential in processes that require this capacity; for example, iron forms part of some antioxidant enzymes, which participate in the neutralisation of oxygen free radicals to prevent cell damage.
Symptoms of its deficiency
Iron deficiencies are striking, as they are characterised by a failure to produce chlorophyll, which is reflected in a loss of green colouring in the leaf. Gradually, the green colour of the leaf will turn yellow, although the nerves will remain green. The loss of green colour always occurs in the young leaves, as iron is not mobile in the plant. This is the most characteristic factor of iron deficiency compared with deficiency of other micronutrients.
Iron Deficiency
Iron deficiency is always a problem of availability and assimilation for the plant.
The solubility of inorganic iron is highly dependent on soil pH.
Soluble or fully available inorganic iron in the soil is achieved at pH 3. By increasing the pH just to 4, only 1% of the iron needs of the crop can be covered. Therefore, at normal soil pHs (5, 5-7), the levels of assimilable inorganic iron for plant roots are non-existent.
Therefore, calcareous soils with a pH above 7 are iron deficient. In this type of soil, in addition to the influence of the pH, there are high amounts of carbonate ions. The carbonate ion affects the uptake of iron and its translocation in the plant, inducing severe iron chlorosis.
Toxicity
Iron toxicity is especially problematic in flooded soils. This type of toxicity is common in crops such as rice. The symptoms of iron toxicity are known as “bronzing”. First the leaves are covered with tiny brown spots, which then turn a uniform brown colour.
As you have just seen in this article, the use of fertilisers with microelements such as iron are necessary for optimal crop development and biochemistry. If you have any doubts about which product is required and how and when to use a fertiliser with iron, we are at your disposal. Please contact us,we will be delighted to talk to you!
