In field experiments during years 2003-2005 potato cultivars were tested at two different levels of soil fertilization to determine the effect of Sonata Z foliar application on the yield and quality features. The lower level of soil fertilization resulted in the marketable yield increase by 13.7%, at the amount of large tubers increased by 13.3%, and the amount of seed tubers by 11.8%. Significantly higher yields were obtained when Sonata Z was applied with urea buffer; total yield increased by 17.2%, and seed potato yield by 24.5%. The microelement contents in Sonata Z, when accompanied by lower fertilization levels, resulted in longer tuberization period and propagation coefficient higher by 14.7%. Foliar fertilization of Sonata Z showed no significant effect on tuber quality and disease infection, however.