Sulfate of potash

SOP is produced from naturally occurring potassium-sulfate-bearing minerals or through processes that react potassium chloride with sulfate sources, yielding a product with a typical guaranteed analysis of around 50% K₂O and 18% sulfur, and minimal chloride.

Chemical formula

K₂SO₄

Potassium content

About 50% K₂O

Sulfur content

About 18%, as sulfate

Chloride content

Minimal, distinguishing it from muriate of potash

SOP supplies potassium, an essential macronutrient, together with sulfate-sulfur, without the substantial chloride load carried by muriate of potash, making it a two-nutrient product favoured where chloride is undesirable.

• Potassium is water-soluble and readily taken up by roots
• Sulfate-sulfur is supplied as a useful secondary nutrient
• Chloride content is low relative to muriate of potash

SOP is commonly used on chloride-sensitive crops, including many fruit, vegetable, and other quality-sensitive crops, and on crops or soils with a concurrent sulfur need, despite its typically higher cost per unit of potassium compared with muriate of potash.

• Preferred where chloride sensitivity affects yield or product quality
• Supplies sulfur alongside potassium
• Suited to fertigation and foliar programs due to good solubility and low salt burden relative to chloride salts

General practice weighs the additional cost of SOP against its chloride-free benefit for sensitive crops, and considers soil potassium and sulfur status alongside the crop’s overall nutrient program.

As a chloride-free source, SOP avoids the localised chloride loading associated with muriate of potash, though potassium can still be subject to leaching on coarse-textured, low-exchange-capacity soils, and sulfate behaves as a mobile anion in the soil solution.