The Influence of Polyhalite Calcium on Selected Club Root and Aspects of Soil Structure.

Polyhalite is an evaporate mineral comprising hydrated sulphates of potassium, calcium and magnesium K₂SO₄.MgSO₄.2CaSO₄.2H₂O.  The importance of K, Mg and S in crop mineral nutrition is well accepted and polyhalite is becoming established as a fertilizer. The objective of these studies was to demonstrate the additional value of calcium to the soil environment from polyhalite above its nutrient value in use as a fertilizer material.

Existing knowledge indicates the effects of conventional fertilisers on soil flora and soil inhabiting disease organisms. Trials in the UK characterised the response of Plasmodiophora brassicae (clubroot disease) populations to application of Polyhalite. Results indicate the potential of polyhalite to supress disease in use as a fertilizer plan component.

Changes to soil physical structure by gypsum driven due to its calcium content are recognised. Resultant effects were found to vary between soils, with calcium poor and mechanically weak soil of 23 kPa from NE Scotland having a linear trend for increased tensile strength with polyhalite applications up to up to 50t/ha from 59.16 kpa. A hard-setting (1500 kpa) Iraqi soil, showed decreasing soil shrinkage following polyhalite amendment.

Polyhalite also contains potassium and magnesium which will likely alter how it interacts with soil. A second trial in this series assessed the response difference between gypsum and polyhalite applied for equal calcium. A calcium rich sandy loam and a potassium rich sandy loam showed differing responses in sorptivity, macroporosity and unconfined compression strength depending on soil type and applied treatments.

Work continues to evaluate the additional benefits of polyhalite beyond its use as a fertilizer.