Commercial diammonium phosphate is sold in several colors — grey, brown, black, amber and yellow — and a number of markets specify one appearance over another by long-established buying convention. Yellow DAP is one such presentation. The compound inside the granule is unchanged: the same (NH₄)₂HPO₄, the same alkaline reaction zone, the same seed-placement rules. This page exists to set out clearly where the color comes from, and to state plainly what it does and does not tell a buyer.
Substance identity
| Field | Value |
|---|---|
| Active compound | Diammonium hydrogen phosphate, (NH₄)₂HPO₄ |
| CAS | 7783-28-0 |
| PubChem CID | 24540 |
| Molar mass | 132.06 g/mol |
| Grade | most commonly supplied as [CAS?] (64 % total nutrient) |
Specification
Typical — verify on certificate of analysis:
| Parameter | Typical |
|---|---|
| Total nutrient (N + P₂O₅) | ≥ 64 % (most common); lower tiers also offered |
| Nitrogen (N), ammoniacal | 18 % |
| P₂O₅, total | 46 % |
| Moisture | ≤ 2.0 % |
| Particle size | ≥ 90 % within 2 – 4 mm |
| Appearance | yellow to amber granules |
| Colorant | where a colorant is used, its identity and inclusion rate should be stated on the specification |
Properties
All chemical and physical properties are those of diammonium phosphate: alkaline solution reaction near pH 8, free ammonia at the dissolving granule, high water solubility, decomposition with ammonia loss on heating, critical relative humidity around 82.5 % at 30 °C.
Where the color comes from. Two distinct mechanisms, and they should not be confused:
- Intrinsic color from raw materials and process route. Wet-process phosphoric acid carries iron, aluminium and organic matter from the source phosphate rock. The type and quantity of that carry-over sets the natural color of the finished granule, which is why product from different rock sources and different plants looks different at identical analysis.
- Added colorant. Where a market has a firm appearance preference, a colorant may be applied to the granule surface to meet it. This is a cosmetic finishing step.
Both mechanisms produce a yellow granule, and they are not distinguishable by eye. If it matters to the buyer whether a colorant has been added, it must be asked and answered on the specification.
Applications
Agronomic use is identical to standard DAP: basal N + P for cereals, maize, rice, cotton, oilseeds and sugarcane; drilled or broadcast and incorporated; blended with urea, ammonium sulfate and potash. Best suited to neutral and acid soils; on strongly calcareous soils MAP is generally the better phosphate. The seed-placement caution applies in full — free ammonia from the alkaline granule reaction injures germinating seed, so side-band rather than seed-place, and use MAP where seed-placed phosphate is required.
The one genuinely practical use of granule color: visual differentiation in the field and in the store. A distinct color makes it easy to confirm at a glance which product went into a spreader or a blend hopper, and to detect mixing of two products in a shared bin. That is a stock-control benefit, not an agronomic one.
Handling and storage
As for standard DAP: dry covered ventilated storage, sealed packaging, stock rotation, strict segregation from lime and other alkaline materials, away from strong acids and heat, ventilation in bulk storage. One additional point: surface colorants can transfer to hands, packaging and equipment, particularly on damp product. Where a colorant is present, confirm that it is handled and disposed of in line with its own safety data sheet.
Notes
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Color is not a grade. A yellow granule may be 64 % total nutrient or a lower tier. The analysis is on the certificate, not on the granule.
-
Color is not a purity claim. A lighter or brighter granule does not evidence lower impurity, particularly where a colorant has been applied.
- The only documents that establish what is in the product are the declared analysis and the certificate of analysis for the lot.