Buying zinc sulphate fertilizer in bulk means settling four things before you sign: the hydrate and form your customers need, the COA values the supplier must meet, the price basis you compare offers on, and how the cargo stays dry on the way to your warehouse. For the wider picture on trace elements, see our [micronutrient fertilizer overview](/blog-article/enhancing-crop-nutrition-with-micronutrient-fertilizers).
What zinc sulphate fertilizer is
Zinc sulphate (ZnSO4) is the zinc salt of sulphuric acid and the most widely used zinc fertilizer worldwide. It supplies two nutrients, zinc and sulphur, in a water-soluble form. Growers use it to correct zinc deficiency through soil application, blends, fortified NPK, fertigation, and foliar sprays. The trade sells it as a monohydrate or a heptahydrate. (International Zinc Association, Zinc Fertilizer Overview)
US suppliers list the same product as zinc sulfate fertilizer.
Monohydrate vs heptahydrate
Zinc sulphate monohydrate (ZnSO4·H2O) carries one molecule of water and contains about 36% Zn. Zinc sulphate heptahydrate (ZnSO4·7H2O) carries seven and contains about 22% Zn (International Zinc Association). The heptahydrate takes up water more readily and is less stable in storage, so its zinc content can drift lower over time (Pacific Fertiliser).
| | Monohydrate | Heptahydrate |
|---|---|---|
| Formula | ZnSO4·H2O | ZnSO4·7H2O |
| Zn content (IZA) | 36% | 22% |
| Zn content (Scapex, theoretical) | 36.4% | 22.7% |
| Water solubility (IZA) | Highly soluble | Highly soluble |
| Storage stability | More stable | Absorbs water more readily |
Sources: International Zinc Association, Scapex Exports, Pacific Fertiliser.
Because the monohydrate packs more zinc into each kg, freight and handling cost less per kg of zinc delivered.
Granular vs powder grades
Both hydrates are traded as granules or powder, and Pacific Fertiliser lists both forms for blending (Pacific Fertiliser).
Granular for bulk blending and direct application
Granular zinc sulphate goes to bulk blenders and distributors who mix it with urea, DAP, MOP, or ammonium sulphate, or who spread it straight onto the field. The granule size needs to match the other blend components, or the zinc will segregate in the spreader. Ask for a size distribution on the COA.
Powder/crystal for NPK, liquid and foliar formulations
Powder and crystal grades go to compound NPK plants that fortify their granules with zinc, and to formulators of liquid, fertigation, and foliar products. These buyers need fast, complete dissolution, so they pay attention to water insolubles and free acid. The heptahydrate is often chosen for foliar sprays and fertigation work.
What grade labels like 33% or 21% mean
A grade label such as "zinc sulphate 33%" is a declared minimum zinc content, expressed as % Zn by weight of product. Scapex describes 21% Zn as typical for fertilizer heptahydrate and 33% or 35% Zn for monohydrate (Scapex Exports). Write the minimum into the contract and check it lot by lot.
Specs to check on the COA
A zinc sulphate COA should state Zn %, S %, water solubility or water insolubles, free acid or pH, moisture, and granule size, plus lead, cadmium, arsenic, and mercury. Each line needs a test method and the issuing lab. Fertilizer grades are controlled for free acid, insolubles, and heavy metals (Scapex Exports).
| Parameter | Why it matters |
|---|---|
| Zn % | The nutrient you pay for; check against the declared grade |
| S % | Second nutrient; often declared on the label |
| Water solubility | Affects how quickly the zinc reaches the crop and how well it dissolves in tanks |
| Free acid / pH | High acid can corrode equipment and cause caking |
| Moisture | Drives caking and lowers Zn per kg |
| Granule size | Blend segregation and spreading |
| Lead | Contaminant often limited by destination rules |
| Cadmium | Contaminant often limited by destination rules |
| Arsenic | Contaminant often limited by destination rules |
| Mercury | Contaminant often limited by destination rules |
| Insolubles | Nozzle blockage in liquid and foliar use |
Packaging, shipping and storage
Bulk zinc sulphate usually moves in 25 kg or 50 kg bags with a moisture-resistant liner, or in big bags (FIBCs) for blenders. State the bag weight in kg, the liner, and the pallet pattern in the contract. Keep the product dry. Moisture causes caking, and the heptahydrate is especially prone to taking up water (Pacific Fertiliser). Check containers for dryness before loading and store bags off the floor.
How bulk zinc sulphate is priced
Zinc sulphate price offers are quoted on a weight basis for the product, usually FOB at the load port, CFR at your discharge port, or DAP (Delivered at Place) for container and regional trades. The main drivers are zinc raw material costs, grade, hydrate, form, packaging, and freight.
Monohydrate and heptahydrate prices are not comparable kg for kg. Convert each offer to cost per kg of Zn landed at your warehouse, including freight, insurance, port charges, duties, and bagging.
Supplier checks for importers
To vet a zinc sulphate supplier, confirm the producing plant, ask what zinc raw material it uses, and request COAs from recent shipments that include heavy metal results. Test a sample in your own lab and appoint an independent surveyor to sample and weigh at loading. Use payment terms tied to inspection.
- Ask whether the plant uses zinc ore concentrate, zinc oxide, or recycled zinc materials, because the source affects which contaminants turn up.
- If the seller is a trader, they should name the producer, and the certificate of origin should match.
- Ask for real shipment COAs, not only a typical spec sheet.
- Test lead, cadmium, arsenic, and mercury against your destination limits.
- Have the surveyor confirm Zn %, moisture, and granule size at loading.
- Avoid large advances to unproven sellers. Letters of credit or staged payments are safer.
For comparable checklists on other products, see our guides to [bulk ammonium sulfate](/blog-article/how-to-buy-bulk-ammonium-sulfate-fertilizer-importers) and [bulk NPK fertilizer](/blog-article/how-to-buy-bulk-npk-fertilizer-importers).
Import compliance
Many markets require fertilizer registration before sale, micronutrient labeling with declared Zn and S content, and limits on heavy metals such as cadmium and lead. Scapex lists the HS code for zinc sulphate as 2833.29 (Scapex Exports). We have not cited specific limits here. Confirm registration, labeling, contaminant limits, and customs classification with local authorities and your customs broker before you ship.
FAQ
What is zinc sulphate fertilizer?
Zinc sulphate fertilizer is a water-soluble salt that supplies zinc and sulphur to crops. It is the most widely used zinc fertilizer worldwide, according to the International Zinc Association. Importers sell granular material to blenders and distributors and powder or crystal to NPK plants and to liquid and foliar formulators, in monohydrate or heptahydrate form.
What is the difference between monohydrate and heptahydrate?
The monohydrate holds one water molecule and contains about 36% Zn. The heptahydrate holds seven and contains about 22% Zn, per the International Zinc Association. The monohydrate packs more zinc into each kg and stores better. The heptahydrate takes up water more readily and is often used for foliar and fertigation products. Compare offers on cost per kg of Zn.
Should I buy granular or powder zinc sulphate?
Buy granular zinc sulphate if your customers are bulk blenders or spread it directly, and match its size to the other blend components. Buy powder or crystal if you supply NPK granulation plants or formulators of liquid, fertigation, or foliar products, since they need fast dissolution. Check water insolubles and free acid on the COA for those buyers.
How is bulk zinc sulphate priced?
Bulk zinc sulphate is quoted on a weight basis for the product, usually FOB or CFR, with DAP terms in some container trades. Zinc raw material costs, grade, hydrate, form, packaging, and freight all move the price. Convert every offer to cost per kg of Zn landed at your warehouse before comparing.
Ready to source or sell zinc sulphate? Post a zinc sulphate buy request on GetFertilizer with your hydrate, grade, COA specs, quantity in kg, packing, and delivery terms, or list your product if you are a supplier.