Ketema Tezera*, Aynalem Gurms, Gobena Dirirsa, Tatek Wondimu, Tigist Worku, Tilahun Hordofa, Abera Tesfaye and Gebeyehu Ashemi
Irrigation is a vital practice in the Central Rift Valley of Ethiopia. However, water scarcity is the major limiting factor to agricultural production and productivity in the area. A field experiment was conducted on clay loam soil at the experimental field of Melkassa Agricultural Research Centre with the objectives of determining optimal Nitrogen fertilizer rate and soil moisture level for the onion yield and water productivity. The experiment was arranged in split-plot design with three replications. The treatments include three soil moisture levels (100% ETc, 75% ETc and 50% ETc) as main plot and four nitrogen fertilizer rates of 23, 46, 69, 92 and no nitrogen as a sub-plot. The highest average bulb yield of 28.6 t/ha was obtained at the full application of irrigation(100% ETc) and the lowest average bulb yield of 22.8 t/ha was recorded at 50% level of irrigation deficit. Onion bulb yield increased significantly with an increase in nitrogen fertilization from 23 to 92 N rate kg/ha. The highest average bulb yield of 30.1 t/ha was obtained at the 92 Kg/ha N rate and the lowest average bulb yield of 20.1 t/ha was recorded from no application of nitrogen rate. The highest bulb yield of 33.1 t/ha was recorded from the fully irrigated that combined with high nitrogen levels. Moisture stress at different deficit levels with the nitrogen levels had a significant (p<0.05) influence on water productivity. Water productivity was higher for 92 N-rate kg/ha treatment and minimum water productivity was obtained at zero nitrogen rate treatment. Therefore, under a limited water area, it can be concluded that more water-saving and an associated increase in water productivity with high nitrogen fertilizer resulting in a yield increment of the onion by 32.5% can solve the problem of water shortage.
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