MKP or SOP? Choosing the Right Potassium Fertilizer for the Stage You're At

Two bags on the same shelf can both promise potassium and still serve completely different purposes. NPK 00:52:34, commonly called MKP (mono-potassium phosphate), and NPK 00:00:50, commonly called SOP (sulphate of potash), are a good example. Both are nitrogen-free, both dissolve fully in water, and both are popular in fertigation programs — but growers reach for them at different points in the season, for different reasons.

MKP — potassium with a phosphorus partner

MKP carries potassium alongside a substantial dose of phosphorus, and no nitrogen at all. That combination makes it a common choice around the flowering and fruit-set stage, when a crop benefits from both nutrients together — phosphorus to support flower and root activity, potassium to support the fruit that's just beginning to form — without adding more nitrogen, which at that stage can sometimes push vegetative growth at the expense of flowering.

SOP — potassium on its own

SOP, by contrast, supplies potassium and sulphur with no phosphorus and no nitrogen. It tends to come into the schedule later, during fruit development and maturity, when the crop's phosphorus needs have already tapered off but potassium demand is still high — potassium plays a direct role in fruit size, sugar content and overall quality as the crop matures.

One more practical difference: SOP is chloride-free, sourced as a sulphate rather than a chloride salt. For crops that are sensitive to chloride — tobacco, certain fruits and some vegetables — sulphate-based potassium sources like SOP are generally preferred over chloride-based ones for this reason.

• MKP (00:52:34) — phosphorus + potassium, used around flowering / fruit-set
• SOP (00:00:50) — potassium only, used around fruit development / maturity
• Neither carries nitrogen, so both fit late-stage schedules where nitrogen is being tapered down
• SOP is chloride-free, which matters for chloride-sensitive crops

So which one do you actually need?

It usually comes down to where the crop is in its cycle and what else it needs alongside the potassium. If phosphorus is still wanted for flowering, MKP does double duty. If phosphorus has already been applied and the crop just needs a potassium push through fruit maturity, SOP is the more direct choice. Many nutrition schedules actually use both, one after the other, rather than picking a single grade for the whole season.

Sunraj Fertilizers stocks both grades under the Meridian brand — MERIDIAN 00:52:34 and MERIDIAN 00:00:50 — in 1 KG and 25 KG packs. If you're not sure which stage your crop is at or which grade to start with, message us on WhatsApp with your crop and current stage, and we'll help you figure it out.