Sulphate of Potash (SOP), chemically known as Potassium Sulphate (K₂SO₄), is a premium potash fertilizer supplying two essential nutrients—potassium (K) and sulfur (S). Being completely chloride-free, SOP is especially suitable for fruits, vegetables, tobacco, tea, coffee, and other high-value and chloride-sensitive crops.
Product Identification
| Parameter | Specification |
|---|---|
| Chemical Name | Potassium Sulphate |
| Chemical Formula | K₂SO₄ |
| Fertilizer Grade | 0-0-50-18S |
| Category | Chloride-free potassic fertilizer |
| Nature | Naturally occurring / chemically processed potassium salt |
Chemical Composition & Structure
| Component | Typical Content |
|---|---|
| Potassium (as K₂O) | 50–52% |
| Sulfur (as S) | 17–18% |
| Chloride (Cl⁻) | ≤ 1.5% |
| Sodium (Na) | ≤ 1.0% |
| Magnesium (Mg) | ≤ 0.5% |
| Moisture | ≤ 0.5% |
SOP is an ionic compound composed of potassium (K⁺) and sulfate (SO₄²⁻) ions. It behaves as a neutral salt in soil and is completely free from chloride, making it safe for sensitive crops and light soils.
Physical Properties
| Property | Typical Value |
|---|---|
| Appearance | White crystalline or granular solid |
| Bulk Density | 1.1 – 1.3 g/cm³ |
| Particle Size | 1 – 4 mm (granular SOP) |
| Solubility in Water | ~11 g/100 g at 25 °C |
| Hygroscopicity | Low |
| Melting Point | ~1069 °C |
Mechanical Properties (Granule Performance)
✔ Granule crush strength: 3–5 kg/granule
✔ High abrasion resistance
✔ Very low dust generation
✔ Low caking tendency
📌 SOP granules are strong, dense, and free-flowing, ideal for bulk handling and precision fertilizer application.
Strengthening & Crystallization Behavior
Granule strength is derived from:
✔ Stable orthorhombic crystal lattice
✔ Strong ionic bonding
✔ Controlled crystallization or compaction processes
📌 No metallurgical behavior applies (non-metallic salt)
Thermal & Chemical Behavior
Thermal Stability:
Highly stable during storage and field use
Does not decompose under agricultural temperatures
Melts only at very high temperature (~1069 °C)
Chemical Reactivity:
Non-volatile
Does not significantly increase soil salinity
Sulfate sulfur is immediately available to plants
Key Agronomic Characteristics
✔ Supplies potassium and sulfur
✔ Enhances sugar formation and protein synthesis
✔ Improves oil content in oilseed crops
✔ Improves fruit color, size, and shelf life
✔ Increases resistance to drought and disease
Processing & Refining Properties
Manufacturing Routes:
✔ Mannheim process (KCl + H₂SO₄ → K₂SO₄ + HCl)
✔ Natural SOP mining (langbeinite, kainite)
✔ Double salt conversion processes
Process Controls:
Temperature control
Acid recovery (HCl)
Granule size uniformity
Moisture management
Available Forms
Granular SOP (soil application)
Powder SOP (fertilizer blending)
Water-soluble SOP (fertigation)
SOP-M (Mannheim grade)
Applications
Agriculture:
Fruits (grapes, citrus, banana)
Vegetables (potato, tomato, onion)
Tobacco, tea, coffee
Sugarcane and oilseeds
📌 Especially beneficial for chloride-sensitive crops
Industrial:
Glass manufacturing
Specialty chemicals
Pharmaceuticals
Food-grade potassium salts (after refining)
Advantages of SOP
Agronomic:
✔ Chloride-free potassium source
✔ Supplies sulfur (often deficient in soils)
✔ Improves crop quality and taste
✔ Safe for saline and light soils
Commercial:
✔ High purity product
✔ Premium fertilizer category
✔ Enhances export-grade produce quality
✔ Stable storage and handling
Limitations & Considerations
Lower K₂O content compared to MOP
Higher cost per unit potassium
Limited global availability
Slower dissolution compared to potassium nitrate
SOP vs Other Potassic Fertilizers
| Parameter | SOP | MOP | KNO₃ |
|---|---|---|---|
| K₂O (%) | 50 | 60 | 44 |
| Sulfur | Yes | No | No |
| Chloride | Nil | High | Nil |
| Crop Quality | Excellent | Moderate | Excellent |
| Cost | High | Low | Very High |
Why Choose SOP?
✔ Best potassium fertilizer for quality crops
✔ Essential for chloride-sensitive plants
✔ Dual nutrient supply (K + S)
✔ Improves export-grade produce
✔ Supports sustainable soil health
Storage & Handling
Store in dry, ventilated areas
Avoid contamination with chlorides
Use moisture-proof bags
Follow FIFO inventory management
Soil Suitability Summary
| Soil Type | Suitability |
|---|---|
| Neutral soils | Excellent |
| Acidic soils | Excellent |
| Saline soils | Very good |
| Sulfur-deficient soils | Excellent |