Smaller details

• Potassium chloride and potassium sulphate can be mined and be used as a source of potassium.

  Phosphate rock is also mined. However, because the phosphate salts in the rock are insoluble plants can't directly absorb them.

  Reacting phosphate rock with a number of different types of acids produces soluble phosphate.
• Potassium compounds + nitric acid --> phosphoric acid and calcium nitrate
• Potassium compounds + sulphuric acid --> calcium sulphate + single superphosphate (calcium phosphate)
• Potassium compounds + phosphoric acid --> calcium phosphate (triple superphosphate).