Zinc micronutrients: properties and applications

Zinc micronutrients are a group of substances that provide plants with available zinc — a trace element that plays a critical role in enzymatic processes, pigment synthesis and growth regulation. Zinc deficiency is widespread on calcareous, limed and neutral soils and leads to reduced yields, deterioration of product quality and increased plant susceptibility to diseases. Zinc fertilizers are used for pre-sowing seed treatment, foliar feeding and basic soil application.

Chemical Nature and Range

The main representative of zinc micronutrients is zinc sulfate (zinc vitriol, ZnSO₄·7H₂O), containing 22% zinc. It is colourless crystals or white powder, readily soluble in water. Zinc sulfate is widely used due to its high solubility and rapid release of zinc ions upon application. In addition to sulfate, other forms are used in agriculture: powdered zinc-containing products (18–22% Zn), poly micronutrients, frits and zinc chelates (Zn-EDTA, Zn-DTPA). Chelated forms have high bioavailability and are especially effective on calcareous and alkaline soils, where zinc ions can bind into compounds unavailable to plants.

Modern producers offer zinc fertilizers in various forms: crystalline, powder and liquid (concentrates). Liquid forms are convenient for precise dosing during foliar feeding, while crystalline and powder forms are used for pre-sowing seed treatment and basic application.

Regulatory Framework

Requirements for zinc vitriol as a fertilizer and technical product in Russia and CIS countries are regulated by GOST 8723-82. According to the standard, the product must contain at least 21.8–22.5% zinc and comply with impurity standards (iron, copper and others). For chelated forms of zinc, manufacturers' technical specifications and international quality standards apply.

Agronomic Value and Applications

Zinc is a cofactor of more than 300 enzymes involved in the synthesis of proteins, carbohydrates and auxins (growth hormones). It is necessary for pollen formation, seed development and stress resistance. With zinc deficiency, plants exhibit small leaves, rosetting, chlorosis of young leaves, shortened internodes and reduced yields. Zinc fertilizers allow these disorders to be eliminated, increase yields and improve biofortification of products (zinc content in grain and fruits).

Main methods of applying zinc fertilizers:

• Pre-sowing seed treatment. Spraying seeds with 0.1% zinc sulfate solution (2–4 L/c) or dusting with zinc-containing powder (200–500 g/c). This improves germination and initial growth.

• Foliar feeding. Spraying plants with 0.05–0.1% zinc sulfate solution (100–300 L/ha) during the growing season. Feeding is carried out in phases of intensive growth and fruit formation.

• Basic soil application. Zinc sulfate or zinc chelates are applied before digging or cultivation. Application rates depend on soil zinc availability and crop biological characteristics.

The most responsive crops to zinc are fruit and vegetable crops, sugar beet, cotton, corn, and cereals. Zinc fertilizers are especially effective on sod-calcareous, limed sod-podzolic soils, calcareous chernozems and serozems with neutral or near-neutral reaction.

Safety and Storage

Zinc sulfate belongs to substances of moderate hazard. When working with it, personal protective equipment (respirator, safety goggles, gloves) is recommended to prevent irritation of mucous membranes and skin. Storage is carried out in dry, well-ventilated areas, in hermetically sealed containers, away from food products and feed. The shelf life of zinc fertilizers under proper storage conditions is several years.

Conclusion

Zinc micronutrients remain an important tool for combating zinc deficiency and increasing crop productivity. The variety of forms — from traditional zinc sulfate to modern chelated complexes — allows the optimal product to be selected for specific soil and climatic conditions and cultivation technology. Organising supplies of zinc fertilizers, including the selection of form and concentration, requires an individual approach.