Summary:

We evaluated how organic manures (farmyard manure, dung water and poultry slurry), different doses of mineral fertilizers (three treatments), combinations of manures with mineral fertilizers (three treatments), and potato varieties (four varieties) influenced potato tuber yields in our long-term fertilizer experiment in Prague, established in 1954.
According to our crop rotation, potatoes were planted every ninth year, starting in 1962. Four potato varieties were used since then (Krasava, Radka, Korela, Dita), all of them were medium-maturing and consumable.
The average potato yield was 19.1 Mg ha-1 at the beginning of our experiment (1962, var. Krasava) and 37.5 Mg ha-1 in 2007 (var. Dita), showing low suitability of the experimental site for potato production. The mean tuber yield of varieties Krasava, Radka, Korela and Dita was 18.5, 17.1, 30.2 and 37.5 Mg ha-1, respectively. The effect of organic manures was principally comparable with mineral fertilizers. Increasing doses of mineral fertilizers were not related to appropriate increase in tuber yield. Therefore, application of N, P and K around 50, 50 and 144 kg ha-1, respectively, gives fair yields in such non-optimal production area, as is our experimental site. In the case of warm and dry seasons, even high doses of the mineral fertilizers can't ensure usual potato production.