Abstract: Swiss chard is recognized as valuable leafy vegetable species with short growing period suitable for cultivation as forecrop and aftercrop in crop rotation .Till now is still a minor crop in Poland and there are not existing any data describing the response of this species to nitrogen fertilization and the effect of this nutrient on plant composition. In a field experiment conducted in 2004–2006, the influence of nitrogen fertilization applied as a single or split dose in the amounts of 50, 100, 100 + 50, 150, 150 + 50 and 200 kg∙ha^-1 on yield and crop quality of Swiss chard was examined. Seeds of Lukullus cv. were sown directly into the field in the half of April in spacing 45 × 25 cm, and single harvest of leaf rosettes was conducted on 8–10 July. In separate samples of leaf blades and petioles there was evaluated the content of dry matter, vitamin C, sugars, total N, nitrates, P, K, Ca, and Mg. Results of the study indicate that the increment of N dose from 50 to 100 kg∙ha^-1 had positive effects on Swiss chard yield but the efficiency of higher nitrogen doses was rather small and not significant. Heavy nitrogen fertilization caused the increment of total N and nitrates in both edible parts and magnesium in leaf petioles, while reduction the sugar content in leaf blades. On the average blades contained higher amounts of dry matter, sugars, total N and Mg, while petioles – calcium and nitrates.

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