This work as a factorial based on randomized complete block design was carried out with three replications in Mohaghegh Ardabili University’s research Field in 2006.First factor was nitrogen fertilizer (0, 80, 160 and 200 kg/ha net Nitrogen) and second was tuber size (<40, 40-80 and >80 gr). Results showed that incrimination of tuber size accelerated complete germination and onset of appearance of tubers and incrimination of nitrogen application led to delay in time of complete germination, appearance of stolons and onset of tubering in field. The most tuber yield, number of tuber, mean tuber weight and tuber dry weight were achieved in medium tuber size, Also, the most tuber yield, mean tuber weight and tuber dry weight were gained at 160 kgha-1net nitrogen. So, utilization of 160 kgha-1 nitrogen with medium tuber size in order to achieving most yields and planting usages is recommended.