This experiment was conducted in Agricultural Research Center of Hamedan to study the effect of nitrogen fertilizer on the growth and yield of potato as well as the relationship between nitrogen application rate and nitrate accumulation in tubers of potato varieties. Two potato varieties (Diamant and Marfona) and six nitrogen rates (based on soil analysis and including 86.2, 129.4, 172.5, 215.6, 258.7 and 345 kgN/ha ) were taken to be arranged factorially in a Randomized Complete Block Design of three replications. During the growth season, date of emergence, flowering, tuber formation as well as complete soil coverage, and at harvesting time, the number of tubers and stems per plant, tuber weight and finaly yield were measured. After harvest, nitrate rate in tubers was determined. Results showed that with increase in nitrogen rate, dates of flowering and tuber formation were delayed, whereas complete soil coverage was accelerated. Nitrogen fertilizer had no significant effect on the number of tubers and stems per plant but the effect of variety was significant. The effects of variety and nitrogen fertilizer on tuber weight and yield were significant. Tuber weight and yield in Marfona ( 72.5 gr and 34004 kg/ha respectively ) was higher than in Diamant. Nitrate concentration in tubers increased with increasing nitrogen application and was the highest (239 mg/kg ) with 345 kgN /ha. The results in this experiment showed that nitrogen application based on soil analysis leads to suitable tuber yield with acceptable levels of nitrate concentration .
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