Summary:

The aim of the study was to determine the effect of supplementary irrigation and nitrogen fertilization and storage on chosen parameters of chemical composi-tion of early potato cultivars. Field experiment was carried out at Kruszyn Krajeń-ski nar. Bydgoszcz in 2005-2007 on the very light soil. The experiment was estab-lished as the three-factorial trial with three replications. The first order factor were cultivars – ‘Dorota’ and ‘Gracja’, the second order factor was sprinkler ir-rigation applied in two variants: W0- without irrigation (control), W₁ - sprinkler irrigation according to indications of tensiometers (the soil water potential higher than -0,03 MPa). The third order factor was differentiated nitrogen fertilization: N₀ = 0 kg N∙ ha^-1 , N₁ = 40 kg N∙ ha^-1, N₂ = 80 kg N∙ ha^-1 , N₃ = 120 kg N ∙ha^-1. It was found that the dry matter and starch content was significantly differ-entiated for the investigated cultivars, irrigation and nitrogen doses, after harvest and after storage. Irrigation decreased significantly the content of dry matter and starch as well as this factor increased slightly the content of vitamin C, reduc-ing sugars and total sugars. Increasing nitrogen doses (to 80 kg N∙ ha^-1) caused the significant increase of dry matter and starch as well as (to 120 kg N ∙ha^-1) the significant increase of reducing sugars. Storage of tubers caused the increase of the content of dry master, reducing sugars and total sugars, but it caused the decrease of the starch and vitamin C contents. Optimum nitrogen dose for the tested cultivars ‘Dorota’ and ‘Gracja’ was 80 kg N ∙ha^-1.