Recognising and correcting magnesium deficiency: kieserite, Epsom salt or Patentkali?
As the central atom of chlorophyll, magnesium is essential for photosynthesis – and magnesium deficiency is widespread on light, sandy soils and where potassium fertilisation is high. Correcting it means choosing between three magnesium-sulphur fertilizers: kieserite, Epsom salt and Patentkali. This article explains the differences and the right application.
Recognising magnesium deficiency
Magnesium deficiency shows first on the older leaves, because the plant moves magnesium to the younger leaves. Typical symptoms:
The deficiency is favoured by light, sandy soils (leaching), cool wet conditions, and high potassium or ammonium inputs that antagonistically suppress magnesium uptake.
Kieserite, Epsom salt and Patentkali compared
All three are chloride-free magnesium-sulphur sources, but differ in form, solubility and accompanying nutrient:
| Product | Nutrients | Form | Use |
|---|---|---|---|
| Kieserite (MgSO₄·H₂O) | ~25% MgO + S | granular, slow-release | Soil base dressing |
| Epsom salt (MgSO₄·7H₂O) | ~16% MgO + S | fully water-soluble | Foliar, fertigation |
| Patentkali (K₂SO₄·MgSO₄) | K₂O + MgO + S | granular | Combined potassium + magnesium |
Kieserite and Epsom salt supply pure magnesium plus sulphur. Patentkali (potassium magnesium sulphate) additionally combines potassium – useful when potassium and magnesium are both lacking.
Soil or foliar application?
The choice depends on urgency and goal:
In practice, foliar and soil applications are often combined: kieserite for base supply, Epsom salt for fast correction.
Sourcing through Cerantis
Cerantis supplies magnesium sulphate in both grades – kieserite (granular, ~25% MgO) for soil and Epsom salt (soluble, ~16% MgO) for foliar and fertigation. The minimum order quantity for specialty fertilizers is 1 MT (subject to product availability and delivery location). Patentkali as a combined K+Mg source can be discussed case by case.
