SOP — Sulphate of Potash (0-0-50)
The premium, chloride-free potash. On quality-sensitive fruit and vegetables it earns its higher price; on a bulk field crop, MOP is the sensible choice.
- Composition
- 50% K₂O, 18% Sulphur, no chloride
- Form
- White powder / granules
- Price
- Premium (dearer than MOP)
- Best for
- Fruit, veg & chloride-sensitive crops
Overview
SOP supplies about 50% potassium (K₂O) plus 18% sulphur, and crucially it contains no chloride. Potassium drives fruit size, colour, sugar and shelf life, and for crops sensitive to chloride — grapes, potato, tobacco, chilli, many vegetables and fruit — the chloride in ordinary MOP can dull quality and, in salty soils, add to salt stress.
That is what SOP is for: the same potassium job, done without chloride and with a bonus of sulphur. It costs meaningfully more than MOP, so the rule of thumb is simple — use MOP on bulk, chloride-tolerant field crops, and pay the SOP premium where produce quality, or a chloride-sensitive crop, justifies it.
What it is and when to reach for it
- A chloride-free potassium source with sulphur — reach for it on grapes, tobacco, chilli, potato and quality-driven fruit and vegetables.
- Use it where chloride would hurt produce quality or on salty soils where extra chloride adds to salt stress.
- On bulk, chloride-tolerant cereals and sugarcane, MOP does the same potassium job for less.
How to apply it well
- Apply as basal, or split with a top dressing at the fruit/tuber development stage on high-potash crops.
- It is also available in a water-soluble grade for drip fertigation on fruit and vegetables.
- Because it adds sulphur too, it can cover part of a sulphur requirement at the same time.
Common mistakes
- Paying the SOP premium on a bulk cereal or sugarcane crop that tolerates chloride perfectly well.
- Skipping potash altogether on quality crops because SOP looks expensive — under-potassed fruit loses size and shelf life.
- Treating it as a complete fertiliser — it carries no nitrogen or phosphorus.
Organic alternative
Wood ash
Wood ash is a chloride-free potash source for organic systems, though far weaker and more variable than SOP; use on acidic soils, sparingly.
Crops it is used on
Open a crop for its full nutrient schedule.
Common questions
MOP or SOP — what is the difference?
Both supply potassium, but MOP (0-0-60) contains chloride and is cheaper, while SOP (0-0-50) is chloride-free and adds sulphur, at a higher price. Use MOP on bulk, chloride-tolerant field crops; use SOP on chloride-sensitive, quality-driven crops like grapes, tobacco, chilli, potato and many fruit and vegetables.
Why is SOP better for fruit and vegetables?
Because it carries no chloride, which can reduce quality in sensitive crops, and it supplies sulphur alongside potassium. The potassium improves fruit size, colour, sugar and shelf life without the chloride load that MOP would add.
Is SOP worth the extra cost?
On quality-sensitive or chloride-sensitive crops — grapes, tobacco, chilli, potato, many vegetables — yes, the quality gain justifies the premium. On bulk cereals, sugarcane and other chloride-tolerant crops, MOP delivers the same potassium for less and SOP is not worth it.
Composition and doses follow ICAR / Soil Health Card guidance; prices are the notified subsidised rates for the season shown and are guidance, not a quote. A soil test for your field always beats a general rate. See our editorial policy.