Sorghum [Sorghum bicolor (L.) Moench] an important food crop in Ethiopia is ranked second for “injera” quality next to tef. However, the productivity of sorghum is constrained by many biotic and abiotic factors amongst striga hermonthica (Del.) Benth is the most specialized root-parasitic weed inflicting serious injury by depriving water, minerals and photosynthesis from the host. Striga hermonthica is becoming the major epidemic in most of sorghum growing areas in the country including Abergelle. Thus, a field experiment was conducted during the 2013/14 cropping season to assess the interaction effect of variety by nitrogen fertilizer rates on striga control, yield and yield related attributes as well as to identify striga resistant variety with optimum nitrogen fertilizer rate to enhance the productivity of sorghum under natural striga infestation areas of Abergelle district, Northern Ethiopia. The treatment combination comprised of two striga resistant and early maturing sorghum varieties (Gobye and Abshir) and three nitrogen fertilizer levels (0, 50 and 100 kg N ha- 1) in a factorial arrangement in randomized complete block design (RCBD) with three replications. The analysis of variance result showed that there were highly significant (P≤0.01) differences due to nitrogen, variety and variety by nitrogen interaction for number of striga count per plot. The lowest number of striga count per plot was obtained from the combination of Gobye+100 kg N ha-1, whereas, the highest number of striga count per plot was recorded from Abshir+0 kg N ha-1. Thus, Gobye exhibited resistance to striga hermonthica by supporting the lowest number of striga plants germination with increasing fertilizer levels from zero to 100 kg N ha-1. Similarly, the analyzed result also showed that grain yield of sorghum was highly significantly influenced (P≤0.01) due to variety by nitrogen interaction effect. The highest grain yield of sorghum (1743 kg ha-1) was obtained from the combination of Gobye+100 kg N ha-1 while the lowest grain yield (1743 kg ha-1) was recorded from Abshir+0 kg N ha-1. However, days to physiological maturity and growth traits like plant height and panicle length were not significantly affected by variety x nitrogen interaction effect. Moreover, the partial budget analysis revealed that the highest net benefit was recorded from the combination of Gobye+100 kg N ha-1. From this, it can be concluded that farmers in the study area could sustainably control striga and enhance sorghum productivity through combination use of the early matured and striga resistant variety Gobye+100 kg N ha-1 under natural striga infestation of Abergelle areas.

Keywords: Variety x nitrogen interaction, Sorghum, Striga hermonthica, Yield and yield related traits.