Performance of Polyhalite As a Multi Nutrient Fertilizer for Potato in Brazil.

Limited peer reviewed information exist on the effect of polyhalite (K₂SO₄.MgSO₄.2CaSO₄.2H₂O), an emerging multi nutrient fertilizer, alternative or complementary source to KCl (MOP), on potato yield and quality. It is essential to understand the availability of nutrients from polyhalite before its wide usage at field scale in either straight or blended form. We established two trials one at Tapira and another one at Casa Branca in Brazil, on loamy soil in 2015-2016. The treatments were, blends made with potassium chloride (MOP+), potassium sulfate (SOP+), and polyhalite (POLY+) as K source at different K rates (0, 62, 124, 187 and 249 kg ha^-1) besides Control. Control was furnished with N and P but not K, Ca, Mg and S. Blend MOP+ lack Mg nutrient but has non-limiting Ca, and S. Blend SOP+ and POLY+ contain similar K, Ca, Mg and S nutrients. Foliar and petiole nutrient concentrations were determined at three growth stages and tuber yield and quality parameters were recorded besides changes to post-harvest soil nutrient values. At Tapira, both SOP+ and POLY+ recorded 29 tons ha^-1 of tuber yield, an extra higher yield of 4 and 7 tons ha^-1 over MOP+ blend and Control, respectively, indicating the contribution of Mg to tuber yields. At Casa Branca, blends MOP+, SOP+ and POLY+ recorded similar but higher yields than that of Control indicating the contribution of K to tuber yields. Data from foliar, petiole, and tuber nutrient concentrations and its uptake indicate the availability of K, Ca, Mg and S from POLY to the potato under southeast humid tropical conditions of Brazil.