Water-soluble Sulphate of Potash (0-0-50) in paddy

Sulphate of Potash (SOP), chemically potassium sulphate (K2SO4), is a chloride-free potassium fertiliser carrying approximately 50% K2O along with 17-18% sulphur. The water-soluble grade is used as a foliar potassium source in paddy at booting and panicle initiation to improve grain weight and panicle development without the chloride loading of granular Muriate Of Potash.

Composition

Grade: 0-0-50 (K2O), plus ~17-18% S
Form: water-soluble crystalline solid
Chloride content: nil (chloride-free)
Indian suppliers: SPIC, IFFCO and importers; notified under the FCO water-soluble fertiliser (WSF) schedule

Mode of action

Foliar-applied potassium sulphate dissolves into K+ and SO4(2-) ions in the spray solution. Both ions are absorbed through the cuticle and stomata and translocated systemically. The K supports cell turgor, photosynthate transport and grain filling, while the S contributes to amino acid and protein synthesis. The absence of chloride avoids leaf-tip burn in sensitive varieties and avoids the chloride loading that limits MOP use in chloride-sensitive crops such as tobacco and grapes.

Target use and dose

In paddy, foliar SOP sprays are typically given at:

Booting / panicle initiation (around 50-60 DAT, see Paddy Third Dose Fertilizer): 0.5-1% solution (5-10 g per litre), to support grain filling and improve test weight.
Mid-grain-fill: optional second spray to address visible K deficiency or to push test weight under heat stress.

Soil-applied SOP can substitute MOP entirely where the chloride load must be avoided, but at substantially higher cost per unit K. In paddy, foliar use is the standard cost-effective entry point.

Safety and regulatory status

Notified under the FCO water-soluble fertiliser schedule. Non-toxic at field rates. The water-soluble grade should be stored dry; humidity causes caking and reduces solubility.

References

Water Soluble Fertilizers. SPIC.
Water Soluble Fertilizers. Gujarat State Fertilizers & Chemicals.