Micronutrient Fertilizers – Zinc Fertilizers

I. Types of Zinc Fertilizers

Zinc fertilizers are materials that provide zinc as a primary nutrient for plants. Commonly used zinc fertilizers in the market include zinc sulfate, zinc chloride, zinc carbonate, chelated zinc, and zinc oxide. Among these, zinc sulfate heptahydrate (ZnSO4·7H2O, containing approximately 23% Zn) and zinc chloride (ZnCl2, containing approximately 47.5% Zn) are commonly used. Both of these are white crystalline substances that are easily soluble in water, and care should be taken to prevent zinc salts from being fixed by phosphorus during application.

II. Forms and Functions of Zinc Fertilizers
Zinc is one of the essential micronutrients for plants, absorbed in the form of the cation Zn2+. The mobility of zinc within plants is moderate. Zinc indirectly influences the synthesis of growth hormones in crops; when zinc is deficient, the content of growth hormones in stems and buds decreases, causing growth to stagnate and resulting in shorter plants. Additionally, zinc acts as an activator for many enzymes, having a broad impact on carbon and nitrogen metabolism in plants, thereby aiding photosynthesis. Zinc also enhances plants’ resistance to stress, increases grain weight, and alters the ratio of seeds to stems.

III. Application of Zinc Fertilizers
When the effective zinc content in the soil is between 0.5 mg/kg and 1.0 mg/kg, applying zinc fertilizers in calcareous soils and high-yield fields can still increase yields and improve crop quality. Application techniques for zinc fertilizers include using them as basal fertilizers, topdressing, and seed fertilizers. Insoluble zinc fertilizers are typically used as basal fertilizers, with an application rate of 1-2 kg of zinc sulfate per acre, which can be mixed with physiologically acidic fertilizers. For fields with mild zinc deficiency, reapplication should occur every 1-2 years; for moderately deficient fields, application can be reduced and conducted every year or every other year. As topdressing, zinc fertilizers are often used as foliar sprays, with a typical concentration of 0.02%-0.1% zinc sulfate solution for general crops, and 0.1%-0.5% for corn and rice. Rice can be sprayed with a 0.2% zinc sulfate solution at the tillering, booting, and flowering stages; fruit trees can be sprayed with a 5% zinc sulfate solution one month before bud break, and after bud break, a 3%-4% concentration can be applied. One-year-old branches can be treated 2-3 times or sprayed with a 0.2% zinc sulfate solution in early summer.

IV. Characteristics of Zinc Fertilizer Application
1. Zinc fertilizers are particularly effective when applied to zinc-sensitive crops, such as corn, rice, peanuts, soybeans, sugar beets, beans, fruit trees, and tomatoes. 2. Application is recommended in zinc-deficient soils: it is beneficial to apply zinc fertilizers on zinc-deficient soils, while they are not necessary in soils that are not deficient in zinc.