The experiment was founded in the spring of 1999 on the grey brown podzolic soil created from boulder clays. The trees of ‘Golden Delicious’ were planted on rootstock M 26 at 3.5 ×  1.2 m spacing (2381 trees ha^-1). The first factor in the experiment consisted the levels of potassium in the arable soil layer: 12, 16 and 20 mg K∙100 g^-1 of soil d.m., on the basis of annual chemical analyses. The second factor of the investigation was three forms of potassium fertilizers: potassium chloride (KCl), potassium sulphate (K₂SO₄) and potassium nitrate (KNO₃). Each year the analyses of macro- and microelements in the soil and leaves were made. The controlled of potassium fertilization made the possible to maintain the planned potassium levels in the soil. Different potassium levels did not cause the significant differences in yielding of the trees. Different potassium levels and fertilizer forms did not cause any significant changes in flesh firmness, soluble solids, in the weight loss of fruit after harvest as well after storage. The using of fertilizer in the form of potassium sulphate caused an increase of the participation of fruit with bitter pit.

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