Coloured granular ammonium sulphate is compacted granular product to which a pigment or dye has been added during granulation. The colour serves identification — distinguishing one supplier’s product from another, marking a specific blend component so that field mixing errors are visible, or meeting a market convention. It is a cosmetic addition, applied at a very small dose, and it changes nothing about nutrient content or availability.
Substance identity
Ammonium sulfate · (NH₄)₂SO₄ · CAS 7783-20-2 · PubChem CID 6097028 · 132.14 g/mol · dyed granules, typically blue, green, red, yellow or black depending on the market convention; 2–4 mm.
Specification
— typical commercial ranges
| Parameter | Typical range | Note |
|---|---|---|
| Total nitrogen (N) | 20.5 – 21.0 % min | pigment dose is too small to change the assay materially |
| Sulfur (S) | 23 – 24 % | |
| Moisture (H₂O) | ≤ 0.5 % | |
| Particle size, 2 – 4 mm | ≥ 90 % | |
| Crushing strength | 2 – 3 kgf typical | as base compacted granule |
| Colourant | present at well below 0.1 % of product mass | identity of the colourant is contract- and market-specific |
| Bulk density | ≈ 1.0 – 1.1 t/m³ |
Properties
Physically and chemically the granule behaves as uncoloured compacted granular ammonium sulphate: same solubility, same critical relative humidity near 79–81 % at 30 °C, same acidification on nitrification. The one behaviour introduced by dyeing is colour transfer. Surface-applied pigment can mark hands, gloves, hoppers, conveyor belts and standing water, especially when the product is damp. Colour fastness varies with the colourant and with whether it is surface-applied or incorporated into the compaction feed.
Applications
Product identification in markets where multiple nitrogen sources are handled through the same yard, visual verification that a bulk blend contains the intended sulfur component, and brand differentiation in bagged trade. Agronomically the product is used exactly as uncoloured granular ammonium sulphate: broadcast, banded, or blended with granular DAP, MAP, MOP or granular urea in matched particle sizes.
Handling and storage
As for compacted granular ammonium sulphate — dry, covered, away from strong alkalis. Additionally: expect staining of wet surfaces, and avoid using dyed product in glasshouse or high-value ornamental situations where residue on foliage or hard surfaces would be objectionable. Rinse handling equipment before switching to a light-coloured product.
Notes
Two honest points. First, colour is not a quality mark — a dyed granule can be made from any feed, including coke-oven crystal, and the dye can mask the natural colour that would otherwise indicate the route. Judge the product from the certificate of analysis, not the shade. Second, the acceptability of a specific colourant is a regulatory question in the destination market, particularly for crops entering food chains and for products sold as EU fertilising products. Confirm that the colourant used is permitted for the intended market and crop before committing to a shade.