What is Sulphate of Potash (SOP)?

SOP (Potassium Sulphate, (K2SO4),) is an essential fertiliser for high-value, chloride sensitive crops such as fruit, vegetables, avocados, coffee beans, grapes, tree nuts, cocoa, anything grown under glass and in arid and acidic soils. It provides plants with the essential nutrients of potassium (K) and sulphur (S). It can also be known as Potassium Sulphate and has the chemical formula (K2SO4),.


  • Essential for all living things
  • Promotes resistance to disease, drought and frost
  • Improves quality, taste and appearance
  • Required in large quantities for proper plant growth and optimal crop yields


  • Necessary for the formation of chlorophyll and plant proteins
  • Increases crop yields and produce quality

What does Sulphate of Potash (SOP) do?

SOP is a mineral fertiliser and a valuable tool in crop management by positively influencing crop yield and quality. SOP nutrients play an important role in the development of proteins, enzymes and vitamins, as well as improving plant photosynthesis and growth.

It improves nutritional value, taste and appearance (size, colour, and scent), fruit’s resistance to deterioration during transport and storage and its suitability for industrial processing. SOP can improve the uptake of phosphorus, iron, and other micronutrients and helps the plant to be more resistant to drought, frost, insects and many diseases. In sandy soils it can also reduce leaching of cations such as calcium and potassium.

Why Sulphate of Potash?

  • Potassium is essential for life – it’s needed in all living cells
  • It is an essential fertiliser for high-value chloride sensitive crops – vegetables, fruit, tree nuts, coffee, avocados and any crops under glass
  • The world cannot produce enough SOP for current demand from primary sources
  • Primary SOP is generally the lowest-cost of production – harvesting solar evaporation
  • Global demand is ~7 million tpa and growing
  • Australia currently imports all its potash needs
  • Increasing global demand for organic and environmentally friendly Australian grown produce


SOP has little to no chloride and a low Salt Index when compared to alternatives, such as Muriate of Potash (MOP) which contains 45% chloride, making it particularly important in semi-arid regions with salinity problems and for those crops sensitive to chloride such as:

  • Fruits (almonds, apricots, avocados, bananas, citrus, grapes, mangoes, peaches)
  • Berries (including strawberries)
  • Vegetables (lettuces, onions, sweet peppers)
  • Field crops (potatoes, tobacco)
  • Coffee and
  • Flowers

In these crops, SOP cannot be substituted with MOP, making demand inelastic.

Global Arable Land Chart


Growing Global Demand Driven By Global Mega Trends

“SOP is considered one of the most important specialty fertilisers due to its properties and beneficial effects in soil and plant systems.”

Production Methods

There are three principle methods of producing SOP:

1. Natural Brines

About 35% of the world’s SOP production is produced from natural brines via solar evaporation. It is a relatively low-cost primary production method, although there are a limited number of operations where geological endowment, logistics and environmental factors align.

Natural brines, such as that being explored for by Trigg Mining, are the only source of SOP to be certified as organic. For organic certification SOP must come from natural sources with little or no processing, such as solar evaporation.

2. Sulphate Salts Reaction

Potassium chloride (MOP) can be reacted with various sulphate salts, such as sodium sulphate, to produce a double salt and then decomposed to yield potassium sulphate (SOP). Around 20% of the global SOP production comes from this process.

3. Mannheim Process

With little over one half of the world’s SOP requirements produced from brines (35%) and reacted salts (20%) a synthetic process is required to meet total demand. The process to synthetically manufacture SOP is known as the Mannheim process. In this method, potassium chloride (MOP or KCl), is reacted with sulphuric acid (H2SO4) by heating in a furnace at temperatures of approximately 800oC to produce SOP and hydrochloric acid (HCl). A secondary process is then required to produce a soluble grade product.

The cost of production  is highly dependent on the input costs of MOP, sulphuric acid and energy.