Mineral fertilisers in agriculture are key to meeting the food requirements of the predicted 9.8 billion population by 2050. But raw resources of these are finite and their use is beset with problems such cost, access and environmental issues. Furthermore, increases in soil degradation makes it more difficult to meet food demands. This work considers polyhalite, 'POLY4' (K2Ca2Mg(SO4)4.2(H2O)) as a new UK potassium fertiliser resource with the proposal that the base cations it contains, could have additional beneficial effects on soil physical structure. A series of experiments were undertaken to study the effects of POLY4 on soil structural and stability properties and on nutrient behaviour. Initially, small-scale laboratory experiments were used to determine strength and stiffness changes in a wide range of soils after POLY4 addition. Strong responses were found in three of the soil types, with one demonstrating a 156% increase in soil tensile strength. Two soils were selected - Insch series, a sandy loam, and Pow Series, a silt loam, to undergo additional testing after exposure to simulated weathering stresses. Whilst most soil physical properties demonstrated limited evidence of changes from POLY4 or gypsum addition, there were differences in pH and shifts in the availability of the cations between the two treatments. When barley plants were grown, the drying and nutrient uptake from roots had a greater impact than K fertiliser source. Insch soil released soil K+ with application of potash fertiliser. Overall POLY4 did not confer any extra advantage on soil or plant properties over MOP or gypsum use as alternative K, Ca and S sources. POLY4, therefore could provide a suitable alternative K fertiliser. It has the potential to contribute to improving food security, whilst having a similar impact on soil properties to that of current mineral fertiliser options.