Kieserite

Kieserite is mined as a natural evaporite mineral and processed into a granular product for fertilizer use. Its guaranteed analysis is typically expressed as roughly 16% magnesium and 22% sulfur, though exact figures vary somewhat between deposits and manufacturers.

Mineral formula

MgSO₄·H₂O

Magnesium content

Approximately 16% elemental magnesium

Sulfur content

Approximately 22% elemental sulfur, as sulfate

Solubility

Dissolves faster than dolomitic limestone; suitable for blending and some soluble applications

Kieserite supplies magnesium, a secondary macronutrient central to chlorophyll structure and enzyme activation, and sulfate-sulfur, a nutrient required for amino acid and protein synthesis, in a moderately soluble mineral form.

• Magnesium is supplied in sulfate form, which is more soluble than carbonate sources
• Sulfur is supplied as sulfate, immediately available to plants
• Contributes negligible change to soil pH compared with liming materials

Kieserite is used to correct or prevent magnesium deficiency on crops such as potato, sugar beet, and grape, particularly on soils where liming is not needed or already adequate, and where a faster-acting magnesium source than dolomitic limestone is preferred.

• Corrects magnesium deficiency without a substantial liming effect
• Supplies sulfur alongside magnesium in a single material
• Can be blended into compound fertilizers or applied as a straight product

General practice is to confirm magnesium deficiency or a magnesium-to-potassium imbalance through soil or tissue testing before application, since excess potassium fertilization can induce or worsen magnesium deficiency independent of the soil’s total magnesium supply.

Sulfate-sulfur from kieserite behaves similarly to sulfate from other fertilizers in soil, remaining mobile and subject to some leaching on sandy or high-rainfall soils, while magnesium is retained on the soil’s cation exchange sites to a degree that depends on the exchange capacity present.