Ammonium Sulphate (21-0-0+24S) is a dual-nutrient fertilizer providing both nitrogen (21%) and sulphur (24%). While it contains less nitrogen than Urea, its sulphur content makes it uniquely valuable for sulphur-deficient soils and crops with high sulphur demand.
Nutrient Profile
- Nitrogen (N): 21% — Present entirely as ammonium (NH4+), the preferred form for acidic and alkaline soils
- Sulphur (S): 24% — Present as sulphate (SO4-2), immediately available for plant uptake
- Phosphorus (P): 0% — No phosphorus content
- Potassium (K): 0% — No potassium content
Key Agricultural Uses
Alkaline Soil Amendment
Ammonium sulphate has an acidifying effect on soil. When ammonium ions are converted to nitrate by soil bacteria (nitrification), hydrogen ions are released, gradually lowering soil pH. This makes ammonium sulphate the ideal nitrogen source for alkaline soils (pH above 7.0) where it simultaneously provides nutrition and helps correct high pH.
Sulphur-Deficient Crops
Many tropical and subtropical soils are naturally low in sulphur due to high leaching rates and limited organic matter. Crops that respond strongly to sulphur include:
- Oil Palm: Sulphur is essential for oil synthesis; deficiency reduces bunch weight and oil content
- Tea: Sulphur improves amino acid production, enhancing tea flavor and quality
- Coffee: Sulphur increases bean size and cup quality
- Rubber: Sulphur is required for latex production
- Cruciferous Vegetables: Cabbage, broccoli, cauliflower, and mustard have high sulphur demand
- Onions and Garlic: Sulphur compounds create the characteristic flavor and pungency
Top Dressing for Nitrogen
Ammonium sulphate works well as a top-dressing nitrogen source during vegetative growth stages. Its ammonium form is held by soil particles and released gradually, reducing leaching losses compared to nitrate-based fertilizers in high-rainfall environments.
Application Rates
- Oil Palm: 2-4 kg per palm per year, split into 2-3 applications during rainy season
- Tea: 200-400 kg/ha per year, split into 4-6 applications
- Rubber: 100-200 g per tree per year during tapping years
- Vegetables: 150-300 kg/ha incorporated before planting or as side dressing
- Rice: 100-200 kg/ha as alternative to urea in alkaline paddy soils
- Maize: 150-250 kg/ha at planting or early vegetative stages
Advantages Over Urea
While Urea 46-0-0 provides more nitrogen per bag, ammonium sulphate offers specific advantages:
- Sulphur nutrition: Delivers 24% sulphur that urea cannot provide
- Less volatilization: Ammonium is less prone to gaseous loss from soil surface compared to urea
- Soil acidification: Beneficial for alkaline soils where urea has neutral effect
- Lower salt index: Safer for seed placement and sensitive crops
- Compatibility: Can be blended with most other fertilizers without chemical reaction
Limitations
- Lower nitrogen: Only 21% N means more product needed per hectare compared to urea
- Acidifying: Not suitable for already acidic soils (pH below 5.5) where further acidification is harmful
- Cost per kg N: Higher cost per unit of nitrogen compared to urea
Blending with Other Fertilizers
Ammonium sulphate is compatible with most fertilizers and can be blended with:
- DAP 18-46-0 for combined N-P-S nutrition
- MOP 0-0-60 for N-K-S nutrition
- Rock phosphate for long-term P-S nutrition
Do not blend with lime, calcium ammonium nitrate, or alkaline materials as this causes ammonia loss.
Storage and Handling
Ammonium sulphate stores well under normal conditions. It is less hygroscopic than urea and has low caking tendency. Store on pallets in a covered warehouse. Shelf life: 18-24 months in proper storage.
Bulk Supply from Thai Fertilizer
We supply Ammonium Sulphate 21-0-0+24S in 50kg bags, 25kg retail bags, and 1000kg jumbo bags. Contact us for pricing or chat on WhatsApp for recommendations on sulphur nutrition programs.