effect of nitrogen levels on water use efficiency, grain yield and yield components of corn under optimum and drought stress conditions

in order to study the effects of drought stress and nitrogen (n) levels on grain yield, yield components and water use efficiency of grain corn (sc.704), a field experiment was conducted in 2009 growing season. the experiment was split-plot based on randomized complete block design arrangement and four replicates. main plots were three irrigation levels included optimum irrigation (i1), moderate stress (i2) and sever stress (i3) (irrigation based on depletion of 50%, 60% and 70% of field capacity soil water, respectively). sub-plots included three levels of nitrogen (n1=120, n2=180 and n3=240 kg n ha-1). results indicated that, drought stress reduced biological yield (by), grain yield (gy) and other yield components, significantly. nitrogen imposed a significant effect on gy and yield components. grain yield reduction in moderate and sever drought stress compared with optimum conditions was 15.4% and 37%, respectively. nitrogen application had a positive effect in gy and by under optimum and moderate stress treatments. gy reduction in sever drought stress and low n rates was due to lower grain per ear and 1000-grain weight. the highest and the lowest water use efficiency (economic and biologic) were in optimum irrigation and sever drought stress, respectively. also the highest water use efficiency was belonged to optimum irrigation and 240 kg n ha-1 treatments.