Contrasting Effects of MOP and Polyhalite As a Source of Potassium on Corn Grain Yield Under Southern Highlands of Tanzania.

Recent works on the effect of Muriate of potash on crop grain yields coupled with exploration of new multi nutrient potassium fertilizers such as polyhalite motivated establishing six corn trials at  in southern highland region of Tanzania under rainfed conditions in 2015. The objective is to know whether 20 Kg of K2O from two different sources beyond the recommended practise of 120-60-0 kg ha-¹ N, P₂O₅ and K₂O respectively helps in increasing corn grain yields.  Tested treatments were: 1) Control in which no fertilizer was applied 2) Recommended practise 120-60-0, 3) NPK-MOP, receiving 120-60-20, 4) NPK – Polyhalite, receiving 120-60-20 5) NPK-synthetic polyhalite, receiving 120-60-20  kg ha-¹ N, P₂O₅ and K₂O, respectively. Synthetic polyhalite was prepared by mixing MOP and Kieserite. Variables measured include grain yield, stover weight, number of cobs, vigour and test weight. Treatments of interest were compared by using single degree freedom linear contrasts. As expected all treatments significantly outperformed control at five out of six locations. Recommended practise, NPK-polyhalite and NPK-synthetic polyhalite recorded significantly higher grain yields than NPK-MOP at one, two and two out of six locations respectively and recorded numerically higher grain yields at four, five and five locations out of six. On an average across the six locations they recorded a higher grain yield of 357, 621 and 662 kg ha ^-1 respectively.