In order to study the effect of seed deterioration, plant density and nitrogen fertilizer application on yield, yield components and somequalitative traits of wheat, a field experiment was conducted in Golestan province of Iran, as split factorial in the randomized completeblock design, with four replications in two growing seasons, 2014-2015 and 2015-2016. The experimental treatments included seedquality at 4 levels (control, 15, 30, and 45 hours of accelerated deterioration), plant density at two levels (350 and 420 plants/m) and nitrogen consumption at 3 levels (recommended rate, 15 and 30 percentages higher than the recommended rate, i.e., 125, 143.75, and162.5 kg N fertilizer ha, respectively). All quantitative traits (plant height, spike length, number of seeds per spike, number of spikeletsper spike, weight of 1000 seed, grain yield, straw yield, biological yield and harvest index) and quality traits (yield and protein content,nitrogen content, yield and starch content) were significantly different in different years. Application of recommended rate of nitrogenfertilizer in the first and the second year resulted in the highest average of number of seeds per spike and spike length. The highestgrain yield was achieved in the recommended and 30% higher than the recommended application rate of nitrogen fertilizer (4061.9 and4166.3 kg/ha, respectively) in the second year. Seed deterioration caused a significant reduction in yield and the yield components, sothe highest level of seed deteriorations in the first and the second years decreased 34.11 and 22.63% of the grain yield compared tothe control treatment. The highest protein content was achieved in the second year with the application of nitrogen 30% higher than therecommended rate (with a mean of 623.6 kg/ha), which increased by about 23% compared to the overall average. Seed deteriorationreduced the starch content, so that the highest mean was in non-deterioration in the second year (68.13%), which increased by 10%compared with that of the overall average. The lowest starch content was achieved at the highest level of deterioration (45 hours) in thefirst year (55.63%). In general, the results indicated that seed deterioration had negative effects on quantitative and some qualitativetraits, but the application of more nitrogen fertilizer and higher plant density reduced the negative effects of deterioration and improvedgrain yield and quality.
