The Response of UK Grown Winter Barley to Polyhalite Fertiliser.

Being a natural mineral containing 4 out of the 6 essential macro nutrients, polyhalite (K₂SO₄.MgSO₄.2CaSO₄.2H₂O) offers an extra option to farmers as a fertilizer.  An experiment was conducted in winter barley (Hordeum vulgare L.) at the University of Warwick’s Crop Centre in 2013-14 on a low K (52 ppm) sandy loam soil.  Polyhalite, MOP, MOP + Gypsum (balanced for S content as in Polyhalite) and SOP were compared in a randomized complete block design at 50, 100 and 150 kg K2O ha ^-1 in fall in addition to control (No K and No S).  At the same rates but applied in spring, the first three mentioned treatments were also evaluated for shoot number, normalized difference vegetation index (NDVI), grain yield, and post- harvest residual soil pH and EC.  Due to high (xx mm) fall rainfall, spring application resulted in significantly higher NDVI and grain yields than fall application.  Polyhalite, SOP and MOP + Gypsum were similar for NDVI, above ground biomass and grain yields but out-yielded MOP.  These results show the importance of sulphur since MOP on its own offered no advantage compared to the control despite optimal levels of K being available to the crop.  Polyhalite is an effective source of potassium and sulphur as measured by crop yield, nutrient uptake and fertiliser recovery values.  No significant difference among treatments was observed for residual soil pH and EC.  Based on input costs, barley farmers can consider polyhalite as an option to meet the crop K and S needs.