Farmers in Fedis district, eastern Ethiopia, cultivate onion from unknown seed sources and small bulb sizes, which lead to low bulb yield and short shelf life. No research information on postharvest handling of onion in lowlands of eastern Harerghe zone. The framers also apply different fertilizers in different rates without considering the post harvest loss of the crop. Considering these problems, a field experiment was conducted at the Fedis Agricultural Research Center, during the main cropping season of 2013/2014 to investigate effect of nitrogen application on shelf life of onion varieties. The results revealed that nitrogen rate significantly (P<0.05) affected physiological bulb weight loss, sprouted bulbs, rotten bulbs and reducing sugars. Significant interaction effects of nitrogen rate and variety were observed in TSS content of bulbs. Application of 200 kg N ha-1 decreased total soluble solids and reducing sugars by about 7 and 26%, respectively, as compared to control treatment. In general, application of 100 kg N ha-1 significantly reduced physiological weight loss, rotten and sprouted bulbs by about 4, 7 and 10 %, respectively, than application of 150 kg N ha-1; and by about 9, 9 and 10%, respectively, than the application of 200 kg N ha-1 at 90 days after storage periods. Variety Nasik Red was significantly different in reducing rotten, sprouted bulbs and increasing reducing sugar over the Bombay and Adama Red. Rotten bulbs did not found until 60 days of storage for the three varieties. Nasik Red was found to be superior in quality performance under Fedis condition among the other tested varieties. In conclusion, application of 100 kg N ha-1 and using the variety Nasik Red resulted in maximum postharvest quality of the bulbs in the study area, implying that application of this rate of N fertilizer to this variety results in optimum bulb postharvest quality in the study area.
