Potato Response to Polyhalite Blends Compared to Other Sources of Potassium in Brazil.

Polyhalite is a new fertilizer as source of potassium; it has a low chlorine content (2.5 - 2.8% Cl) and still supply other nutrients to plants (calcium, magnesium and sulphur). However, there is not information about the response of potato to polyhalite in Brazil. Two experiments were carried out to compare the effects of polyhalite (POLY), to muriate of potash (MOP), sulfate of potash (SOP) and sulfate of potash magnesia (SOPM), on potato grown in two sites located in São Paulo (Experiment 1) and Minas Gerais States (Experiment 2), Brazil. The treatments were arranged in a complete randomized block design for both studies with four replicates. Fertilizers were applied as blend (4-14-08) at rates of 0, 200, 300, 400 and 500 kg K2O/ha (Experiment 1). For experiment 2, the blends (4-14-08, 4-14-06, 4-14-04 and 4-14-02) supplied the same rates of N and P2O5 and 0, 75, 150, 225 and 300 kg K2O/ha. Nutrient concentration and uptake by tubers, yield, tuber dry mass percentage and soil analysis before planting and after harvest were analyzed for both studies. For experiment 1, POLY was similar to MOP and increased the N, P, K and Mg uptakes by potato tubers as compared to control. Although POLY has increased 3.7% and 5.5% the total and commercial yield as compared to MOP, these values were not statistically significant. POLY increased the Mg and S contents in the soil as compared to MOP and control. For experiment 2, the nutrient uptakes by tubers were not affected by the sources of fertilizers. The total yield and S content increased 15.1% and 42%, respectively, with POLY as compared to MOP, at rate of 300 kg K2O/ha. The sources of K2O did not affect statistically the commercial yield, although it was 9% higher with POLY as compared to MOP.