Ammonium sulphate is one of the most widely used nitrogen fertilizers — with 21% nitrogen and 24% sulphur, it delivers two essential nutrients in one product. This guide covers composition, agronomic benefits, application rates, and how it compares to urea.
What Is Ammonium Sulphate?
Ammonium sulphate — (NH₄)₂SO₄ — is an inorganic salt produced as a by-product of caprolactam or coking processes. It appears as white to grey granules, is highly water-soluble, and stable under normal storage conditions.
| Property | Value |
|---|---|
| Chemical formula | (NH₄)₂SO₄ |
| Nitrogen content | 21% (ammoniacal form) |
| Sulphur content | 24% (as sulphate-S) |
| Solubility | 706 g/L at 20°C |
| pH of 1% solution | 5.0–6.0 (slightly acidic) |
| Hygroscopicity | Low — good storage stability |
Ammonium Sulphate vs Urea
| Factor | Ammonium Sulphate | Urea |
|---|---|---|
| Nitrogen content | 21% | 46% |
| Nitrogen form | NH₄⁺ (stable) | Urea → NH₄⁺ → NO₃⁻ |
| Volatilization risk | Very low | High (alkaline/bare soil) |
| Leaching risk | Low (NH₄⁺ held by CEC) | High once converted to NO₃⁻ |
| Sulphur supply | 24% S | None |
| Soil pH effect | Acidifying | Slight acidifying |
| Cost per kg N | Higher | Lower |
| Best soils | Alkaline, sulphur-deficient | Neutral to acidic soils |
Bottom line: Urea wins on cost per unit of nitrogen. Ammonium sulphate wins on efficiency in high-pH soils, low volatilization, and the added value of sulphur nutrition.
Why Sulphur Matters
Sulphur deficiency has become more common since the 1990s as high-analysis, sulphur-free fertilizers displaced sulphur-containing ones. High-demand crops include:
- Oilseeds (rapeseed/canola, sunflower): 20–30 kg S/ha
- Brassicas and alliums (cabbage, broccoli, onion, garlic): 15–25 kg S/ha; sulphur essential for flavour compounds
- Cereals: 10–15 kg S/ha; deficiency causes interveinal chlorosis in young leaves
Sulphate-S in ammonium sulphate is immediately plant-available — unlike elemental sulphur, which must first be oxidized by soil bacteria.
Agronomic Benefits
- Soil acidification: Lowers pH slightly — excellent for alkaline soils (pH 7.5–8.5) where urea volatilization is a major N-loss pathway
- Micronutrient availability: Lower pH increases availability of Fe, Zn, Mn, Cu — valuable in calcareous soils where these are locked up
- Protein quality: Sulphur is a structural component of cysteine and methionine; S fertilization consistently improves grain and seed protein quality
- Slow nitrogen release: NH₄⁺ is held by soil CEC and released gradually, reducing N loss in sandy soils
Application Rates
| Crop Type | Typical Rate | Method |
|---|---|---|
| Wheat / Barley | 100–200 kg/ha | Broadcast + incorporate pre-sowing |
| Maize / Corn | 150–300 kg/ha (split) | Side-dress at planting + V6 stage |
| Oilseed rape | 150–250 kg/ha | Early spring top-dress |
| Vegetables | 100–200 kg/ha (season total) | Fertigation (dissolved in water) |
| Fruit trees | 200–400 kg/ha/year | Split: spring + post-harvest |
| Rice (paddy) | 100–150 kg/ha | Broadcast in standing water |
For fertigation, ammonium sulphate dissolves readily — up to 700 g/L at 20°C. Check compatibility with calcium fertilizers at high concentrations.
Grades and Quality
Agricultural grade: 21% N, 24% S, white to off-white granules (2–4 mm). Standard for bulk fertilizer use. Key quality parameters: N ≥21.0%, moisture ≤0.5%, free acid (as H₂SO₄) ≤0.03%, heavy metals within regulatory limits.
Storage and Handling
- Storage: Dry, cool, well-ventilated warehouse. Avoid contact with concrete floors (hygroscopic caking). Shelf life: 12–24 months when properly stored.
- Packaging: 50 kg woven PP bags or 1,000 kg jumbo bags. 20 ft container ≈ 24–25 MT.
- Compatibility: Do not store or mix with oxidizing agents or alkalis (ammonia release).
Sourcing from China
China is the world’s largest ammonium sulphate producer, primarily from coking and caprolactam by-products. Key sourcing notes:
- HS code: 3102.21; major production provinces: Shandong, Jiangsu, Hebei
- Documents required: COA, MSDS, phytosanitary certificate (if required), fumigation certificate for wooden pallets
- Lead time: 15–25 days ex-works; 4–8 weeks port-to-port depending on destination
Hainan Unifarm Chemical supplies Ammonium Sulphate (21% N, 24% S) in agricultural grade with COA, MSDS, and optional third-party inspection before shipment. See also our Phosphorous Acid, Fulvic Acid, Potassium Humate, and chelated micronutrients including EDTA Fe and EDTA Zn, and trace elements such as sodium molybdate for complete crop nutrition programs. Request pricing via our Contact page.
Frequently Asked Questions
Is ammonium sulphate safe for all soil types?
Ammonium sulphate is best suited to neutral and alkaline soils. In already-acidic soils (pH below 5.5), its acidifying effect can be detrimental over time. Apply at reduced rates with periodic lime applications, or switch to calcium ammonium nitrate (CAN) for highly acidic soils.
What is the minimum order quantity for export?
For bulk agricultural export, typical MOQ is 1 x 20 ft container (approximately 24–25 MT). Smaller trial orders of 1–5 MT are possible for new customers requiring quality verification before full container orders.