Maize is an important food security crop in central rift valley of Ethiopia. Applying excess Nitrogen fertilizer in maize production entails costs to smallholder farmers and results in nitrous oxide emission to the atmosphere exacerbating the problem of climate change. Screening nitrogen use efficient hybrids enables resource poor farmers to reduce cost of production, maintain environmental pollution and enhance crop productivity. This experiment was conducted to determine the effect of nitrogen fertilizer on yield and yield related traits and assess the relationship between yield and nitrogen use efficiency indices. Eight maize hybrids were evaluated at three rates of N fertilizer (0, 32.5 and 65 kg N/ha) using split-plot design with three replications at two locations (Dera and Melkassa) in 2020 main cropping season. The results from analysis of variance (ANOVA) at each location indicated that majority of yield and yield related traits, agronomic and physiological efficiency were significantly influenced either by one or two of the factors (nitrogen and genotype) and/or the interaction effect of the two at both locations. The results of combined ANOVA over locations revealed that the interaction of the three factors (location, nitrogen and genotype) had significant effect on leaf area index, number of kernel per ear, agronomic and physiological efficiency. The hybrids grain yield ranged from 3489 (MH138Q) without nitrogen fertilizer to 8390 kg ha-1 (WE8206) due to application of 65 kg N ha-1. Thus, WE8206 and WE7210 could be recommended for production in the study areas. However, for reliable recommendation the experiment has to be repeated for one more season at both locations.

Keywords: Agronomic efficiency, Grain yield, Nitrogen use efficiency, Physiological efficiency