Over 1995-1997 a two-factor experiment was carried out which aimed at defining whether and, if so, to what extent magnesium fertilisation affects the content of organic acids and potato tuber blackening right after reaching full maturity and after autumn-winter storage. ‘Mila’ table potato cultivar was researched. The experimental factors included: 2 evaluation dates (after harvest and after 6 months of storage) and 5 magnesium fertilisation rates (15, 35, 50, 70, 85 kg MgO·ha^-1) against fixed nitrogen, phosphorus and potassium fertilisation. In the experiment the degree of raw and cooked tuber blackening was evaluated as well as the content of organic acids which cause blackening. Magnesium fertilisation shows a significant effect on the content of organic acids in tubers. The most favourable effect on the content of chlorogenic and citric acid was recorded for 70 kg MgO·ha^-1, while a concentration of ascorbic acid was the highest for 50 kg MgO·ha^-1. Magnesium fertilisation, to the satisfaction of consumers, decreases tuber blackening.

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