The present work gives the results of studies from 1997–2000 whose aim was to specify the influence of varied organic fertilization on the chemical composition of potato tubers. The experiment examined following combinations of organic fertilization: control object (without
organic fertilization), farmyard manure, birdsfoot trefoil, italian ryegrass, birdsfoot trefoil + straw, Italian ryegrass + straw. The underplant crops were sown into spring barley cultivated for seed. After the harvest of spring barley, on the fields with straw, the straw was left crumbled, and on those without straw, it was picked and taken out of the field. The whole biomass of underplant crops was appropriated for the green fertilizer. In the first year after organic fertilization, table potatoes were cultivated. During the potato harvest, from each field average samples of tubers were taken to make the chemical analysis. In the fresh mass of potatoe tubers there were marked: the content of starch, reducing sugars and total sugar, and in the dry mass the content of macroelements. Fertilization of potato with underplant crops in combinations with straw or without it, and also with farmyard manure, increased the content of starch and macroelements, and decreased the content of reducing sugar and total sugar in comparison to control object only with mineral fertilization. The highest content of starch was characteristic of potatoes fertilized with Italian ryegrass and Italian ryegrass + straw, and the highest content of nitrogen was characteristic of the potatoes fertilized with birdsfoot trefoil and with birdsfoot trefoil + straw.