Effect of different times and levels of nitrogen application on growth and grain yield of spring wheat cultivar ‘Ghods’ was studied during 1993-1994 growing season at Karkadj, Agricultural Experiment Station, Collegc of Agriculture, University of Tabriz, by using a split plot design with three replications. Main plots were assigned to five levels of N. fertilizers(0, 40, 80, 120, and 160 kg/ha) and sub plots to five times of applications [all of N fertilizer at planting time(T0), 1/2 at planting time + 1/2 during tillering stage (T1), 1/2 at plantig time +1/2 during heading stage (T2), 1/3 at planting time + 1/3 during tillering and 1/3 at heading stages (T3) and 1/4 at planting time
+1/4 at tillering +1/4 at stem elongation and 1/4 at heading(T4). Evaluation of results showed that No. of spikes/rn2, No. of kernel/spike, number of kernel/rn2, grain yield, biological yield and straw yield were increased significantly when higher levels of N. fertilizer were applied, but thousand kernel weight and harvest index decreased, though insignificantly. The effect of split application of nitrogen on number of kernel/spike, grain yield, biological yield, straw yield, and harvest index was non-significant. The effect of times levels interactions of nitrogen application on all traits under study were not significant. As a whole, application of 160 kg of nitrogen fertilizer/ha produced highest yield (5005.5 kg/ha), while its difference with 120 kg of nitrogen fertilizer/ha was not statistically significant. T1, produced highest grain yield (4391,88 kg/ha), while it did not differ from T0 , T2 and T3 significantly. Higher grain yield, due to higher level of nitrogen fertilizer application, can be accounted for increased number of spike/rn2 and number of kernels/spike.
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