Sulphate of Potash Magnesia (SOPM), also known as Langbeinite or K-Mag, is a naturally occurring, chloride-free mineral fertilizer supplying potassium (K), magnesium (Mg), and sulphur (S) in a single product. It is especially suitable for chloride-sensitive and high-value crops and improves overall soil nutrient balance.
Product Identification
| Parameter | Specification |
|---|---|
| Also Known As | Langbeinite, K-Mag |
| Chemical Formula | K₂SO₄·2MgSO₄ |
| Fertilizer Grade | 0-0-22-22-11 (K₂O-MgO-S) |
| Category | Chloride-free multi-nutrient potassic fertilizer |
| Nature | Naturally occurring mineral, mechanically refined |
Chemical Composition & Structure
| Component | Typical Content |
|---|---|
| Potassium (as K₂O) | 21 – 22% |
| Magnesium (as MgO) | 10 – 11% |
| Sulfur (as S) | 21 – 22% |
| Chloride (Cl⁻) | ≤ 2.5% |
| Sodium (Na) | ≤ 1.0% |
| Moisture | ≤ 0.5% |
SOPM is a double sulfate salt of potassium and magnesium. The nutrients are present in sulfate form, are plant-available, and provide a neutral to slightly acidic soil reaction. The product is mined naturally and does not require chemical acidulation.
Physical Properties
| Property | Typical Value |
|---|---|
| Appearance | Pinkish-grey crystalline / granular solid |
| Bulk Density | 1.2 – 1.3 g/cm³ |
| Particle Size | 1 – 4 mm (granular grade) |
| Solubility in Water | Moderate (slower than SOP) |
| Hygroscopicity | Low |
| Melting Point | >900 °C (decomposes) |
Mechanical Properties (Granule Handling)
✔ Granule crush strength: 3–5 kg/granule
✔ High abrasion resistance
✔ Very low dust formation
✔ Low caking tendency
📌 SOPM granules are hard, dense, and free-flowing, making them excellent for bulk blending and long-distance transport.
Crystal Structure & Stability
✔ Orthorhombic crystal structure
✔ High lattice energy provides mechanical strength
✔ No metallurgical behavior (ionic mineral salt)
Thermal & Chemical Behavior
Thermal Stability:
Stable under storage and field conditions
No nutrient loss at normal agricultural temperatures
Soil Chemical Behavior:
Gradual nutrient release
Sulfate sulfur readily available
Magnesium improves cation balance and chlorophyll formation
Key Agronomic Characteristics
✔ Supplies three essential nutrients in one product
✔ Potassium improves yield and stress tolerance
✔ Magnesium supports chlorophyll and photosynthesis
✔ Sulfur enhances protein and oil synthesis
✔ Improves nitrogen and phosphorus use efficiency
Processing & Refining Properties
Production Method:
Underground mining of langbeinite ore
Crushing and screening
Washing for impurity removal
Granulation (optional)
Drying and conditioning
Key Process Controls:
Particle size uniformity
Moisture reduction
Chloride control
Available Forms
Granular SOPM (field application)
Crystalline SOPM
Blended formulations with DAP, MAP, or Urea
Applications
Agriculture:
Fruits (banana, grapes, citrus)
Vegetables
Sugarcane
Tea and coffee
Oilseeds and potatoes
Excellent for magnesium-deficient soils, sandy soils, and high-yield cropping systems
Advantages of SOPM
Agronomic:
✔ Chloride-free
✔ Multi-nutrient fertilizer (K + Mg + S)
✔ Improves crop quality and color
✔ Enhances photosynthetic efficiency
✔ Reduces need for separate magnesium fertilizers
Commercial:
✔ Naturally mined product
✔ Strong granules with low dust
✔ Easy storage and blending
✔ Cost-effective compared to separate nutrient sources
Limitations & Considerations
Lower K₂O content than MOP and SOP
Slower solubility – not ideal for fertigation
Limited global sources
Higher cost per unit of potassium
SOPM vs SOP vs MOP
| Parameter | SOPM | SOP | MOP |
|---|---|---|---|
| K₂O (%) | 22 | 50 | 60 |
| Magnesium | Yes | No | No |
| Sulfur | Yes | Yes | No |
| Chloride | Nil | Nil | High |
| Best Use | Soil health | Crop quality | Bulk crops |
| Cost | Medium–High | High | Low |
Why Choose SOPM (Langbeinite)?
✔ Best solution for magnesium and sulfur deficiency
✔ Chloride-free potassium source
✔ Improves crop quality and yield stability
✔ Excellent for perennial and plantation crops
✔ Balanced nutrient supply in one application
Storage & Handling
Store in dry, covered warehouses
Avoid prolonged moisture exposure
Use standard fertilizer bags or bulk storage
Follow FIFO inventory practice
Soil Suitability Summary
| Soil Type | Suitability |
|---|---|
| Neutral soils | Excellent |
| Acidic soils | Very good |
| Sandy soils | Excellent |
| Magnesium-deficient soils | Outstanding |