Nitrogen use efficiency of bread wheat: Effects of nitrogen rate and time of application

the experiment was conducted to assess the effects of nitrogen (n) rate and time of application on n use efficiency (nue) of bread wheat, and their association with grain yield and protein content. factorial combinations of four n levels, two bread wheat varieties and three timings of n applications were laid out in a randomized complete block design. n rate significantly influenced grain yield, protein content, n uptake efficiency, n biomass production efficiency, n utilization efficiency, n use efficiency for grain and n use efficiency for protein yield. time of n application had highly significant effect on grain yield, protein content and nue traits. rate of n application and variety were significantly interacted to influence grain yield. grain yield for madda walabu found sharply increase with each increase in n application rate. the improved variety provided significantly higher grain yield, n utilization efficiency and n use efficiency for grain yield (nuegy) when n was applied 1/4 at planting, 1/2 at mid-tillering, and 1/4 at anthesis. variations in nuegy were explained more by the variations in n uptake efficiency. harvest index contribution to nuegy was higher for the local variety. although nue significantly decreased with increasing n rates, yield response of the varieties did not plateau out.