Polyhalite is a multi-nutrient mineral ore containing potassium (K), calcium (Ca), magnesium (Mg) and sulphur (S). Historically, it has enjoyed minor use as a fertilizer, but the opening of a new mine in the UK will make larger quantities available. Therefore, an examination of the performance of crops fertilized with polyhalite, or selected commercial alternatives, was pertinent and is reported here.

Four field trials were carried out between 2013 and 2016 to investigate the response of winter barley (Hordeum vulgare L.) and forage maize (Zea mays L.) to different application rates of polyhalite, potassium chloride (muriate of potash, MOP) and potassium sulphate (sulphate of potash, SOP) fertilizers. Potassium and S nutrition were the focus of these trials as they limit field production more often than Mg and Ca.

Polyhalite was found to be an effective source of both K and S for crop production. In three out of four trials, application of polyhalite resulted in similar or greater K offtake compared with both MOP and SOP; MOP application resulted in greater K offtake in one trial. In three out of four trials, application of polyhalite resulted in similar or better S offtake compared with both MOP and SOP; SOP application resulted in greater S offtake in one trial. Polyhalite and MOP treatments produced similar total dry weight in all four trials, but were slightly inferior to SOP treatment.