Fertilization is one of the most important factors which can significantly affect potato tuber quality. The effect of multi-nutrient complex fertilizers (HydroComplex, Nitrophoska Blue Special and Viking 13 representing the nitrophoska group, and Polimag S from the amophoska group), and single-nutrient fertilizers (ammonium nitrate, single superphosphate and potassium sulphate) on tuber quality of very early potato cultivars (‘Aster’, ‘Fresco’, ‘Gloria’) was compared in a three-year field experiment. It was found that the single-nutrient and multi-nutrient complex fertilizers did not affected the dry matter, starch and L-ascorbic acid content in tubers of very early potato cultivars, but they increased nitrate (V) content. Of the multi-nutrient complex fertilizers, only HydroComplex containing most of magnesium and sulphur of all with the nitrophoska group significantly increased nitrate (V) content in tubers, on average by 4.0 mg N-NO₃ kg^-1 of fresh weight and, as result, reduced the ascorbate-nitrate index, compared with the single-nutrient fertilizers. The fertilizers applied in the study had no effect on the content of mineral compounds in potato tubers, except of potassium. The potassium content increased as the result of HydroComplex applied, on average by 0.86 g kg^-1 of dry matter. The kind of fertilizer had a greater effect on the quality of ‘Aster’ and ‘Gloria’ than ‘Fresco’ tubers. Tubers of ‘Aster’ and ‘Gloria’ contained more dry matter and starch, and less nitrates (V) and calcium than ‘Fresco’. The content of L-ascorbic acid, phosphorus, potassium and magnesium in tubers of the examined potato cultivars was similar.

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