Iron

This element is critical for chlorophyll synthesis, although it is not part of the chlorophyll molecule itself. Without sufficient available iron, pigment biosynthesis is blocked, leading to a sharp decrease in photosynthesis intensity and suppression of the plant's overall development.

In plant tissues, iron participates in atmospheric nitrogen fixation in legumes. It acts as an important component of enzyme systems responsible for nitrate reduction to ammonia, directly influencing the quality and protein content of the yield.

The biological availability of iron in the soil depends heavily on pH levels and aeration. In alkaline soils, the element turns into poorly soluble forms, becoming inaccessible to roots, which necessitates the use of special chelated compounds for plant nutrition.

Unlike macronutrients, iron is required in extremely small doses, yet it lacks the ability to be remobilized within tissues. This means that deficiency symptoms always appear first on young leaves, which cannot "extract" the element from older organs.

The main sign of iron deficiency is interveinal chlorosis — yellowing of the leaf blade while veins remain green. In severe cases, leaves become almost white, and the edges may suffer from necrosis.

High-risk groups include crops grown on carbonate soils with high pH, as well as plants sensitive to micronutrient deficiency: apple trees, grapes, raspberries, tomatoes, and citrus.

Iron excess is extremely rare, occurring mostly in highly acidic soils or due to unjustified over-application of fertilizers. It manifests as bronze spotting on leaves and stunted root system growth.

Iron toxicity is often accompanied by a secondary deficiency of manganese and phosphorus, as iron in high concentrations blocks their uptake. The plant visually appears stiff, and shoot growth slows down significantly.

Iron application is carried out primarily through foliar feeding, as soil application of iron sulfate is ineffective due to rapid element fixation. It is recommended to use chelated forms (Fe-EDTA, Fe-EDDHA), which are stable across a wide soil pH range.

Application rates for foliar sprays typically range from 0.5 to 2 kg of product per hectare, depending on the active ingredient concentration and crop condition. Treatments should be performed during periods of intensive growth when the need for photosynthesis is highest.

For fertigation (root irrigation), Fe-EDDHA iron chelate is used, which remains available to plants even at pH above 7.5. This is the most expensive but economically justified way to combat chlorosis in perennial plantations.

Timing of application is linked to phenological phases: the first treatment occurs at the beginning of leaf emergence, with subsequent ones upon the appearance of the first chlorosis symptoms. The frequency of application depends on soil acidity and field history.

It is strictly recommended not to mix chelated iron forms with copper-based fungicides, as this leads to the destruction of the chelate bond. Another limitation is high irrigation water hardness, which can precipitate the element.