Fertilization of horticultural plants significantly contributes to increased yield but also affects yield quality. Nitrogen, potassium, and sulphur, which belong to the main macronutrients, can have a large effect on the chemical composition of edible parts of plants. The aim of the present study was to determine the effect of the rate of nitrogen as well as of the rate and form of potassium on the accumulation of dry matter, N-NH₄, N-NO₃, Fe, Zn, Mn, and Cu in the leaves of garden rocket grown in a greenhouse during the spring period. These macronutrients were applied at the following rates (in g ^. dm^-3 of medium): 0.3 and 0.6 N in the form of Ca(NO₃)₂; 0.3, 0.6, and 0.9 K in the form of K₂SO₄ and KCl; 0.4 P; 0.2 Mg; as well as the following micronutrients (in mg ∙ dm^-3 of medium): 8.0 Fe (EDTA); 5.1 Mn (MnSO₄ ∙ H₂O), 13.3 Cu (CuSO₄ ∙ 5H₂O), 0.74 Zn (ZnSO₄ ∙ 7H₂O), 1.6 B (H₃BO₃); 3.7 Mo (NH₄)₆Mo₇O₂₄ ∙ 4H₂O). The increased rates of nitrogen and potassium caused significant changes in dry weight (DW) of rocket plants; its higher proportion was found when the lower rate of N was applied, compared to the higher rate. The increased rate of N increased the content of N-NH₄ and N-NO₃, whereas the rising amount of K in the medium resulted in a decrease in the amount of N-NO₃ in the plant material studied. Plants fertilized with the lower rate of nitrogen accumulated more iron and zinc as well as less manganese than plants that received more of this nutrient. Plants fed with the highest rate of K accumulated the largest amount of iron, while the largest amount of manganese was found in plants that received the lowest amount of this nutrient. The application of K₂SO₄, as a source of potassium, contributed to an increased accumulation of iron, whereas the application of KCl resulted in an increased concentration of manganese in rocket leaves.

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