What is SOP and How Does It Differ from MOP?
Potassium Sulphate (SOP, K₂SO₄) and Muriate of Potash (MOP, KCl) are the two main potassium fertilizers available to Indian farmers. Both supply potassium, but they differ critically in the accompanying anion. MOP supplies chloride (Cl⁻) — an ion that many high-value horticultural crops are sensitive to in excess. Chloride accumulation in the root zone can reduce fruit quality, lower brix (sugar content), shorten shelf life, and — in severe cases — cause leaf tip burn and reduced yield. SOP supplies sulphate (SO₄²⁻) instead, which acts as a secondary nutrient (sulphur is a macronutrient) and does not cause these adverse effects. SOP also has a much lower salt index than MOP, making it safer for use on light soils and in fertigation systems where fertilizer concentration in the root zone can be high.
Benefits of SOP for Horticultural Crops
Potassium is the nutrient most strongly linked to fruit quality parameters — and SOP is the form that delivers potassium without the penalties of chloride. Key benefits of SOP application in horticultural crops include: increased fruit size and weight (potassium drives cell expansion and water uptake in developing fruit); improved brix and sweetness (potassium activates sucrose synthase enzymes, increasing sugar accumulation in fruit); better fruit colour (potassium improves anthocyanin biosynthesis in grapes and pomegranate, and lycopene in tomato); extended shelf life (potassium strengthens cell walls and reduces water loss after harvest); improved drought tolerance (potassium regulates stomatal opening, reducing water loss under heat stress); and reduced disease susceptibility (adequate potassium improves cell wall integrity, making plants harder for fungal pathogens to penetrate).
Dosage by Application Method
For drip fertigation — the most efficient delivery method — apply SOP at 3–5 kg per acre per application. Fertigate through the drip system in the morning when soil moisture is optimal, and flush lines with plain water after. For foliar spray, dissolve SOP at 1–2% concentration (10–20 grams per litre of water) and spray in the early morning or evening to minimise leaf burn. Foliar SOP is effective for a rapid potassium boost during fruit fill or when soil application is not practical. For broadcast application before the season, apply 15–25 kg SOP per acre (depending on soil test results and crop demand) and incorporate into the soil before planting or at the start of the irrigation cycle.
Best Crops for SOP Application in India
SOP is the preferred potassium source for the following crops in India: grapes (particularly chloride-sensitive table and wine varieties); pomegranate (where fruit colour and brix are key quality parameters for export); banana (high potassium demand, sensitive to chloride at high rates); tomato (for lycopene content and firmness); chilli (for capsaicin content and fruit weight); strawberry (for brix and shelf life); onion and garlic (for bulb size and dry matter content); leafy greens (spinach, lettuce — where chloride accumulation can cause tip burn); and cucurbits (cucumber, melon — where fruit sweetness and firmness are market quality parameters). MOP remains appropriate for most field crops (wheat, maize, sugarcane) that are not chloride-sensitive and where cost is the primary consideration.
Application Timing for Fruit Crops
Potassium demand in fruit crops peaks from fruit initiation through maturation — this is when cell division, cell expansion, and sugar loading require the highest potassium supply. In grapes, the most critical SOP applications are from berry set through véraison (colour change onset). In pomegranate, apply from 30 days after fruit set through colour development. In tomato and chilli, begin SOP fertigation from first fruit set and continue every 10–14 days through harvest. Avoid heavy SOP application during active vegetative growth (nitrogen is the priority then) or in the post-harvest period. In drip-irrigated orchards, SOP can be included as a standard component of the fertigation programme throughout the fruiting season.
SOP vs MOP Price Difference — Explained
SOP consistently costs more than MOP — in India, MOP is typically available at ₹12–15 per kg, while SOP ranges from ₹25–35 per kg. The price difference exists because SOP production is more complex: most SOP is manufactured by reacting MOP with sulphuric acid (Mannheim process) or derived from natural mineral sources like langbeinite and polyhalite, which require additional processing. However, for high-value horticultural crops, the economics strongly favour SOP. A 5% increase in fruit brix or a 1-week extension in shelf life can far exceed the additional fertilizer cost in premium markets. For export-quality grapes or pomegranate, using MOP instead of SOP risks downgraded produce and price penalties that dwarf the input cost saving. Prodo (SOP from No Brands) starts at ₹250 per kg — significantly below branded SOP products at equivalent purity.
Price of Prodo SOP in India
Prodo (Potassium Sulphate) from No Brands is available starting from ₹250 per kg for standard pack sizes. Branded SOP products from major fertilizer companies are typically priced ₹320–380 per kg for the same nutrient composition (K₂O content 50%, sulphur 17–18%). For a grape vineyard requiring 20–25 kg SOP per acre per season, choosing Prodo over branded SOP saves ₹1,400–3,250 per acre per season without any compromise in nutrient quality. Available in 1 kg, 5 kg, and 25 kg packs on Farmkart, with delivery to major grape and pomegranate growing regions in Maharashtra, Rajasthan, and Karnataka.