عنوان مقاله [English]
To study the nitrogen use efficiency (NUE) and change the attributes associated with it, the field experiments were conducted at the Gorgan University of Agricultural Sciences Research Farm, Gorgan, Iran in the growing seasons of 2007-2008 and 2008-2009 under well watered conditions. The 16 cultivars were sown in a randomized complete block design with three replications. The results showed that during breeding activities to improve wheat yield, NUE and nitrogen utilization efficiency (NUtE) increased 0.28% and 0.31% per year, respectively; while for nitrogen uptake efficiency (NUpE) no changes was observed. Because NUE divided into two components: NUtE and NUpE, most of the breeding effects on NUE were associated with change in nitrogen utilization efficiency (NUtE). Also grain protein concentration (GPC) have been decreased 0.05 %. It seems that in studied cultivars, grain harvest index increased more rapidly than nitrogen harvest index. This problem can explain the decline of grain protein.