In order to study of the effect of Nitrogen fertilizer on yield and yield components and determination the best level of this fertilizer for Agria cultivar of potato (Solanum tuberosum L.), a factorial experiment was conducted based on a Randomized Complete Block Design (RCBD) with tree replications in Ghorveh, Kordestan, Iran. In this research the effects of tree levels of nitrogen fertilizer, 4 different of application times of the fertilizer and interaction of these treatments were studied. The results of variance analysis showed that there are significant differences (P≤0.01) between main treatments and interactions between them. In this study the maximum number of tubers (25.55), the maximum weight of tubers and the maximum number of stems obtained after application of 200 Kg/ha N fertilizer. The maximum tuber yield, the maximum tuber number and the maximum dry weight of tubers were observed in condition that third part of Nitrogen fertilizer used at first and the rest of fertilizer used after Earthling up.
