Zinc sulfate

Zinc sulfate is a hydrated zinc salt supplied mainly as the monohydrate (around 36% zinc) or the heptahydrate (lower zinc content). Both forms are fully water-soluble and supply zinc together with sulfate-sulfur, and the monohydrate’s higher analysis makes it common in dry blends.

Chemical formula

ZnSO₄ (as mono- or heptahydrate)

Zinc content

About 36% in the monohydrate; lower in the heptahydrate

Sulfur content

Supplied alongside zinc as sulfate

Solubility

Fully water-soluble

Zinc sulfate supplies zinc, a micronutrient essential for enzyme function and growth-hormone metabolism, together with sulfate-sulfur. Once in soil, zinc availability falls as pH rises and can be reduced on calcareous, high-phosphorus, or heavily leached soils, which is why deficiency is common in those conditions.

• Zinc is immediately available on dissolving but can be fixed at high soil pH
• Sulfate-sulfur is supplied alongside the zinc
• Deficiency is common on calcareous, sandy, or high-phosphorus soils

Zinc sulfate is used to correct or prevent zinc deficiency in responsive crops such as maize, rice, citrus, and pecan. It can be broadcast or banded into soil, applied as a seed coating, or sprayed on foliage; foliar sprays give a fast response where soil-applied zinc is quickly fixed.

• Soil, seed, and foliar application are all practised
• Foliar sprays give a quick response on high-pH soils where zinc is fixed
• Responsive crops include maize, rice, and citrus

Zinc is needed only in small amounts, and excessive application can be toxic to plants and can accumulate in soil, so it should be applied only where deficiency is confirmed. Soil-applied zinc is readily fixed on high-pH soils, which can favour foliar or banded placement for efficient correction.