Although its exact role is not known, zinc is one of the micronutrients plants need to grow efficiently. It is an essential component of enzymes involved in metabolic reactions. Zinc deficiency symptoms differ among plant species, but common characteristics include striped bands of tissue on the midrib of plant leaves, usually occurring within two to three weeks of germination. Deficiencies can lead to significant decreases in crop productivity and nutritional quality.
Zinc sulfate is the most commonly used source of zinc in granular fertilizers because of its high solubility in water and its relatively low cost of production. Zinc sulfate heptahydrate and zinc sulfate monohydrate have the highest solubility and are suitable for use in all types of soils. A single application of 15 to 30 pounds per acre of zinc sulfate, containing 36 percent Zn, will usually last for two to three years of crop production. Zinc deficiency can also be treated during the growing season by spraying crops with a 0.5 percent zinc sulfate solution at a rate of 20 to 30 gallons per acre.