Potassium Sulfate (SOP 0-0-50)

Potassium sulfate — also written potassium sulphate, and traded as sulphate of potash or SOP — supplies potassium without chloride, and adds sulphur. Those two characteristics decide almost every purchasing decision in its favour.

The chloride question

Chloride sensitivity is real and crop-specific. Table grapes, avocado, tobacco, strawberry and several other high-value crops show reduced quality or visible damage where chloride accumulates. On saline sites, or where irrigation water already carries a chloride load, adding more through the fertilizer programme compounds an existing problem.

Where the crop tolerates chloride and the soil leaches freely, a cheaper chloride-bearing potassium source may be the better commercial decision. Where it does not, this is the product. Our comparison of potassium sources works through that decision in full.

The sulphur point

Atmospheric sulphur deposition has fallen sharply across Europe and North America over the past three decades, and sulphur deficiency now occurs in situations where it once did not. Where a crop needs both potassium and sulphur, SOP covers both in one product.

Practical note on mixing

Its solubility is roughly a third that of nitrate-based potassium sources. It dissolves perfectly well, but under-agitated material settles in the tank and dosing becomes uneven. Allow more water, more agitation and more time, particularly in cold conditions.

For potassium supplied alongside nitrogen during fruit fill, see NPK 11-8-34 + TE.