Response of Bread Wheat Varieties to Application of Nitrogen Fertilizer under Different Irrigation Treatments

The assessment of water deficit stress and timing of nitrogen fertilizer application effects on seed yield and its components in bread wheat cultivars were carried out in a an split split plot experiment based on RCB design with three replications was carried out. Experimental factors consisted of different levels of irrigation (full irrigation, stopping irrigation at heading and anthesis stages) that were assigned to main plots, and four levels of nitrogen fertilizer applications (F1: 20 and100 kg/ha at sowing and tillering stages respectively, F2: 20 and 100 kg/ha at sowing and booting stages respectively, F3: 20, 50 and 50 kg/ha at sowing , tillering and booting stages respectively, F4: 20 , 50 and 50 kg/ha in sowing, tillering and heading stages, respectively) to sub plots and five bread wheat cultivars (Zarrin, Pishgam, Urum, Zare and Mihan) to the sub sub plots. The results showed that mean yield of cultivars was 7.5 t/ha and it was decreased to 6.5 t/ha at stopping irrigation. The highest and lowest yield belonged to Mihan (8.1 t/ha) and Zarrin (5.7 t/ha) cultivars, respectively. Highest yield belonged to Mihan cultivar (9.4 t/ha) under full irrigation and F4 fertilizing treatments. Under deficit water stress condition at heading and flowering stages, the Mihan cultivar produced the highest yield with 8.3 and 8.6 t/ha at F3 and F4 treatments, respectively. Pishgam, Zare and Mihan cultivars responded properly to F2, F3 and F4 fertilizing treatments when irrigation stopped at heading stage, in comparison with F1 fertilizing treatment. Based on drought tolerance indices, Mihan and Pishgam identified as high performance cultivars under both stress and non-stress conditions.