The Effect of Variety, Nitrogen and Phousphorous Fertilization on Growth and Bulb Yield of Onion (Allium Cepa L.) at Wolaita, Southern Ethiopia

Field experiment was conducted to evaluate growth, yield and yield components of different onion (Allium cepa) varaties under different nitrogen and phosphorous levels from May to December, 2012 in wolaita zone Humbo wereda Ampokoysha district of southern Ethiopia. The study consisted of 3 released Onion varieties (Adama Red, Bombe Red and Nafis), 4 levels of nitrogen (0, 23, 46 and 69 kg N ha-1) and 4 levels of phosphorous (0, 23, 46 and 69 kg P2O5 ha-1) in RCB design with three replications. Data were collected for growth, bulb yield and yield components. Analysis of variances (ANOVA) revealed that varieties differed significantly (P?0.05) in plant height, bulb diameter, bulb fresh weight, total bulb yield, marketable yield, harvest index, bulb dry matter content. Nitrogen affected positively and significantly (P < 0.05) plant height produced the bulbs of greatest marketable yield, and total bulb yield where as Phosphorous affected positively and significantly (P < 0.05) plant height, Harvest index, bulb diameter and bulb dry matter content. There was no significant interaction between variety, nitrogen and phosphorous levels for all observed parameters. In this study, the highest bulb yield of 2.72 t/ha was achieved using Nafis variety with application of 69 kg N/ha and 46 kg P2O5/ha. According to the partial budget analysis, the highest economic benefits of 74,096 birr/ha was also obtained using Nafis variety at 69 kg N/ha and 46 kg P2O5/ha. Therefore, Nafis variety with application of 69 kg N/ha and 46 kg P2O5/ha could be appropriate for Onion production in the test area. Keywords: Onion, Variety, Nitrogen, Phosphorus, Growth, Yield, Ethiopia