One of the very important determinate methods in order to better use of nitrogen fertilizers is considering the differences belonging to growth period length in early and late maturing varieties. Surly, two different groups of potato including early and late maturing varieties would have different needs from the aspect of the optimum use rate of nitrogen fertilizer aspect. This experiment carried out in 2004 crop year in agriculture research station of Ardabil city, stated in 10kilometer far from this city in the east (Alarug village). The factors included four levels of nitrogen fertilizer (0, 80,160, and 200kg net nitrogen per hectare) in main plots and two varieties of potato including Agria (late maturing) and Satina (early maturing) in secondary plots. The experiment was conducted as split plot with randomized complete block design with four replications. The results of variance analysis, demonstrated that the main effects of nitrogen and variety was significant in most of the measured traits such as tuber yield per plant. By increasing fertilizer use to 160kg net nitrogen per hectare, tuber yield increased significantly in Agria variety comparing to Satina, and the most tuber yield in final harvest of late maturing Agria variety with 160kg nitrogen per hectare was estimated about 39.43tons per hectare. By increasing nitrogen use to 200kg nitrogen per hectare, tuber yield decreased significantly in both varieties. Results demonstrated that early maturing Satina variety has more tuber and shoot nitrogen percentage and uptake value compared to late maturing Agria variety. Protein percentage in Satina variety and protein yield in Agria variety had the highest value. By increasing nitrogen fertilizer levels, we observed a significant increase in the traits including nitrogen percentage and uptake value of tuber and shoot and also protein percentage.
