Trials to compare the effect of NPS and NPKS fertilisers on spring barley in Sweden have shown surprisingly large yield benefits for NPK, even when grown on potassium rich clay soils. This has been puzzling, and attempts to explain the effect, such as being due to a low K/Mg ratio in the soil, have been discounted.
In a series of trials conducted during 2010-2011 by Yara Sweden we investigated the effect of both potassium chloride and calcium chloride. Compared to combi drilled NPS we gained the same yield increase with MOP based NPKS, and also with NPS + Calcium chloride.
In leaf analysis carried out at Growth Stage 31, calcium chloride did not affect any other analysed nutrient except for the chloride content, while MOP also affected N, P, K, Cl, Ca and Mg.