SJIF IMPACT FACTOR (2015): 5.79 CRDEEP Journals International Journal of Life Sciences Gebregwergis F. et.al., Vol. 5 No. 3 ISSN: 2277-193x Online version available at: www.crdeepjournal.org/ijls 152 International Journal of Life Sciences. Vol. 5 No. 3. 2016. Pp. 152-162 ©Copyright by CRDEEP Journals. All Rights Reserved Full Length Research Paper Effect of Irrigation Depth and Nitrogen Levels on Growth and Bulb Yield of Onion (Allium cepa L.) at Algae, Central Rift Valley of Ethiopia Gebregwergis Fitsum 1 , Kebede Woldetsadik 2 , Yibekal Alemayhu 2 1- Algae ATVET College, Department of Plant Sciences, P.O.Box 77 Algae Ethiopia. 2- Haramaya University, School of Plant Sciences, P.O.Box,138 Dire Daw, Ethiopi.a Introduction Onion (Allium cepa L.) belongs to the genus Allium of the family Alliaceae and it is bulbous, biennial herb which gives off a distinctive and pungent odor when the tissues are crushed (Rai and Yadav, 2005). Onion is one of the most important crops and used both as a vegetable and spice (Barzegar et al., 2008). Onion (Allium cepa L.) is a popular vegetable in Ethiopia and produced in many home gardens and commercially in different parts of the country. Its production is rapidly increasing both under rain-fed condition and irrigation (Fekadu and Dandena, 2006). The area under onion production in the country is increasing from time to time mainly due to its high profitability per unit area and ease of production and increases in small scale irrigation schemes (CSA, 2010). Despite area increase, the average productivity of onion is low and, at present, the national average yield is as low as 10.75 t ha -1 as compared to many African countries and the world average yield of 17.30 t ha -1 (FAO, 2010) due to lack of information on appropriate nitrogen fertilizers and irrigation regimes (Pathak, 1994), soil physical and chemical characteristics, and disease and pest problems (Abbey and Joyce, 2004). Takele (2004) also reported that soil fertility and water availability are the most serious limiting constraints for crop production in Ethiopia. Because of their shallow and un-branched root system, onion and other Alliums are most susceptible compared to many crops in extracting moisture and nutrients. This makes moisture and nitrogen management a key factor in its production. Hence, they require and often respond well to additional fertilizers and supplemental irrigation (Kebede, 2003). In the study area, irrigation is applied without considering the optimum crop water requirements and application of nitrogen is also based on the national recommendation which does not take cultivar and soil fertility and moisture regimes. As a result, inadequate management of irrigation water and fertilizer was considered to be important limiting factor to onion production in the study area. The reasons behind the improper use of water and nitrogen fertilization are that sufficient information on the simultaneous application of water and nitrogen fertilization is not Article history Received: 15-07-2016 Revised: 25-07-2016 Accepted: 09-08-2016 Corresponding Author: Gebregwergis Fitsum Algae ATVET College, Department of Plant Sciences, P.O.Box 77 Algae Ethiopia. Abstract A field experiment was carried out at Algae ATVET College during 2013/14 dry season to determine the effect of irrigation depth and nitrogen levels on growth and bulb yield of onion. The treatments comprised of three irrigation (50, 75 and 100% of crop water requirements (ETc)) and four nitrogen levels (0, 46, 92 and 138 kg ha -1 )which were laid out in a split-plot design using irrigation as main plot and nitrogen level as subplot with three replications. The irrigation was applied throughout the growth season. Data on plant growth and bulb yield were collected and analyzed. The result showed that irrigation and nitrogen levels significantly affected plant height, leaf number per plant, leaf length, average bulb weight, bulb diameter and length, marketable and unmarketable bulb yield, total biomass and bulbs yield, days to maturity and harvest index per plant, except bulb dry matter, which didn’t show significant variation due to application of nitrogen. These parameters, except leaf and bulb length, bulb dry matter, days to maturity and harvest index per plant were also significantly affected by the interaction of irrigation and nitrogen levels. In the present result, application of irrigation water at 100% ETc fertilized with 138 kg N ha -1 recorded the highest total bulb yield (36.78t ha -1 ) and marketable bulb yield (35.62t ha -1 ), but no significant difference was showed with 92 kg N ha -1 with the same irrigation. However, treatment combinations of irrigation at 50 % ETc and no N (control) produced low amount of total bulb yield (19.84 t ha -1 ) and marketable bulb yield (18.43 t ha -1 ).Therefore, use of irrigation water at 100% ETc fertilized with 92 kg N ha -1 could be the best for maximum bulb yield of Bombay Red onion variety in Algae. However, under conditions that water resources are scarce, the crop can be irrigated using 75% ETc level of irrigation water fertilized with 92 kg ha -1 nitrogen. Keywords: Bulb yield, Irrigation, Nitrogen