摘要：Bread wheat is an important staple and cash crop grown by smallholder farmers in the central highlands of Ethiopia. However, the productivity of the crop is constrained by low soil fertility and poor nitrogen fertilizer management in the area. For example, there is limited information on optimum rates and timing of nitrogen fertilizer application in the area. Therefore, a field experiment was conducted for two consecutive years (2014 and 2015) under rain-fed condition to determine the effect of N fertilizer rate and timing of application on grain yield and nitrogen use efficiency of bread wheat. Factorial combinations of three N levels and five application times plus one control were laid out in a randomized complete block design with four replications. The optimum grain yield (6060.04 kg ha−1) was recorded when 240 kg N ha−1 was applied ¼ at sowing, ½ at tillering and ¼ at booting, and it showed no significant additional response to N fertilizer above this rate. Higher N level (360 kg N ha−1) always increased N content in the grain and nitrogen uptake by wheat crop. The best recovery of nitrogen (59.74%) by wheat was found when 120 kg of nitrogen was applied (¼ at sowing, ½ at tillering and ¼ at booting). The nitrogen use efficiency traits decreased with increased N rate (120–360 kg N ha−1) indicating poor N utilization. The split application of nitrogen (¼ at sowing, ½ at tillering and ¼ at booting) produced the highest nitrogen use efficiency traits. The application of 240 kg N ha−1 in three split doses (T5) was required to obtain optimum wheat yield. In addition, increasing the rate of nitrogen beyond 120 kg N ha−1 decreased nitrogen use efficiency traits.
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