Polyhalite As K and S Source to Soybean in Northern São Paulo State, Brazil.

Soybean is the most important crop grown in Brazil. Soybean is the largest user of potassium fertilizers accounting for 35 % of the total K₂O used in Brazil. The objective of the present study was to evaluate, for a second year, polyhalite as a fertilizer for soybean in northern São Paulo State, Brazil, comparing the current 0-18-18 and 4-30-10 blends for soybean made with MOP as the K source with the same blends made with polyhalite+MOP as the K sources. Field studies were conducted within Northern São Paulo State, Brazil on an Oxisol (Typic Hapludox). Grain Zn, Ca, Mg, and S concentration was higher when polyhalite was used as K source for 0-18-18 blend, however, soybean yield was similar to those when 0-18-18 blend made with MOP was used. Also, the results shown for most of variables (leaf petiole nutrient concentration, grain nutrient concentration, amount of nutrients exported by soybean grains, plant biomass, yield) no differences among treatments when 4-30-10 blend, made with polyhalite or MOP, was applied at planting and post emergence K application was applied regardless the K source. In general, the results shown the polihalite can supply K to plants in sufficient quantities compared to MOP. Therefore, it is important to explore polyhalite as new source of K based fertilizers not only to be an alternative for traditional K fertilizers, but also to provide Ca, Mg, S, as well as some micronutrients to soybean.