Every granular fertilizer is sold against a size specification, and most size specifications are weaker than they appear. This page explains what a particle size figure controls in practice for granular agricultural ammonium chloride, and what it fails to control. Blend compatibility is covered on the granular agri-grade page in the main fertilizer products section; this page is about the size specification itself and about distribution uniformity in the field.
Substance identity
| Chemical name | Ammonium chloride |
| Synonyms | Sal ammoniac, muriate of ammonia |
| Formula | NH₄Cl |
| CAS | 12125-02-9 |
| Molar mass | 53.49 g/mol |
| Appearance | White to off-white angular granules |
Specification
| Parameter | Value | Basis |
|---|---|---|
| NH₄Cl content | ≥ 94–96 % | Typical commercial range |
| Nitrogen (N) | ≥ 25.0–25.4 % | Typical commercial range |
| Moisture | ≤ 0.5–1.0 % | Typical commercial range |
| Nominal size band | 2–4 mm is the common cut; 1–2 mm and 3–5 mm are also produced | Typical commercial cuts |
| Percentage within band | State a minimum, e.g. a defined percentage by mass between the two screen sizes | To be agreed — the figure is the specification |
| Oversize above the upper screen | State a maximum | To be agreed |
| Fines below the lower screen | State a maximum, and state whether measured at production or at delivery | To be agreed |
Properties
Chemical properties are unaffected by size: solubility approximately 37 g per 100 g water at 20 °C, endothermic dissolution, 5 % solution pH 4.5–6.0, dissociation on heating with apparent sublimation near 337.6 °C. Size affects rate — dissolution, moisture uptake and caking all scale with surface area, and all three therefore improve as granules get coarser and worsen as fines accumulate.
Applications
What the specification controls. A nominal “2–4 mm” tells you almost nothing on its own. Two products both correctly labelled 2–4 mm can differ substantially: one tightly clustered near 3 mm, the other spread across the full band with material piled at both edges. They spread differently, they segregate differently in a blend, and they cake differently. The useful specification names the screens, the minimum percentage between them, and separate maxima for oversize and for fines.
Why uniformity matters in the field. A spinner spreader sorts by particle mass. Heavy particles fly furthest, light ones fall short, and fines are carried by wind. A product with a wide size spread is therefore separated in flight, and the outcome is a transverse application pattern in which nitrogen rate varies across the working width. The bag analysis stays correct; the field does not receive it uniformly. Narrowing the size distribution is the single most effective way to improve spread uniformity for a given spreader.
Where the fines came from. Fines in a compacted product are generated by attrition during handling, not only produced at the plant. A specification measured at production and a measurement taken at the farm gate can differ substantially, and only the second one describes what will be spread.
Handling and storage
Dry, sealed storage; limit drop heights and transfer points to preserve the distribution. Re-screen where the size specification is critical and the material has been handled repeatedly. Fines concentrate at the base of a heap or bag and cake first, so a partly caked delivery is often a size-distribution problem showing itself rather than a storage failure. No contact with alkaline materials; protect copper alloys and steel in humid conditions.
Notes
Calibrate the spreader with the actual product. Angular compacted granules do not fly like rounded prills, and settings carried over from another fertilizer will not reproduce the same pattern. A tray test at the working width is the only reliable check.