The article presents results of a field experiment involving Blue Congo, an edible potato cultivar with purple-flesh tubers, which is not very common on the Polish market but which may become an alternative to ordinary potatoes owing to its aesthetic and healthful properties. The experiment has proved that more intensive nitrogen fertilisation favours more efficient production and desirable economic output, with a dose of
120 kg N ha-1 being an optimal one, at which the technological effectiveness index equals 20.41. Regarding potassium fertilization, it is not justifiable, neither for production nor for economic results, to exceed a dose of 120 kg K ha-1. Any dose higher than that leads to severe deterioration of the effectiveness indicators. The economic parameters can be improved if market prices are higher, which seems possible when potato tubers are of other colours than the ordinary one.