Effect of Different Nitrogen Levels on Grain Yield, Grain Protein Content and Agronomic Nitrogen Use Efficiency in Wheat Genotypes under Optimum and Post-anthesis Heat Stress Conditions

To study effects of different nitrogen levels on grain yield, grain protein content and agronomic nitrogen use efficiency in wheat genotypes under optimum and post-anthesis heat stress conditions, two separate field experiments were conducted in optimum and delayed sowing dates in Ahwaz, Iran in 2007 and 2008 crop cycles. The experimental site had a mild winter and dry and hot summer. Plants in delayed sowing date experienced heat stress during post-anthesis. Split-plot arrangement were corried out in a randomized complete block design with three replications in each experiment. The N application rates; 50, 100, and 150 KgNha-1 assigned to the main-plots. Sub-plots consisted of six bread and durum wheat genotypes. Results indicated that in both optimum and post-anthesis heat stress conditions, grain yield (GY) decreased significantly as nitrogen level decreased. High temperature during grain filling period reduced the average of grain yield and TGW, 24% and 31%, respectively. Agronomic nitrogen use efficiency (ANUE) reduced as the N level decreased. In post-anthesis heat stress conditions reduction in ANUE was 47.8% as compared with optimum conditions. The average grain protein content (GPC) was between 11-12.6% under optimum and between 12.6-13.8% under post-anthesis heat stress conditions. Higher rates of N fertilizer and also post-anthesis heat stress led to higher GPC. Grain protein yield per unit area increased by 9% under heat stress conditions as compared to optimum conditions. Low GY was associated with high GPC and low protein yield under post-anthesis heat stress conditions.