The nutritional value of some vegetables may greatly vary depending on the cultivation method and kind of fertilization. In 2007–2009 there was conducted a field experiment to evaluate the effects of nitrogen fertilizers (ammonium nitrate, calcium nitrate, ammonium sulphate, urea, Entec-26) and their doses (80, 160 kgN∙ha^-1) on yielding and biological quality of two spinach cultivars (Spokane F₁, Rembrandt F₁) grown for autumn harvest. The use of Entec-26 fertilizer assured the highest mean marketable yield of spinach (12.25 t∙ha^-1). Comparable results were observed for ammonium sulphate and ammonium nitrate while lower yield was obtained in treatment supplied with calcium nitrate. The highest accumulation of nitrates and vitamin C was associated with the application of calcium nitrate and the lowest one with ammonium sulphate and Entec-26. An increase of the dose of fertilizer from 80 to 160 kg N∙ha^-1 did not significantly affect yielding of spinach and its nutritional value expressed by the content of dry matter, vitamin C and nitrates. Among the two cultivars, Rembrandt F₁ produced higher yield of leaves and showed some tendency to a higher accumulation of nitrates, whereas lower content of dry matter and vitamin C. The levels of P, K, Mg and Ca were not dependent on the cultivar as well as kind and dose of nitrogen fertilizer.

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