The field experiment were performed on the site of Werer Agricultural Research Center (Ethiopia) to study optimal irrigation scenario by taking in to account the leaching requirement and drainable excess water for three successive years. Six irrigation treatments were evaluated at different growth stages of onion plant namely at initial growth stage four irrigation event 23 mm (T1), 16.2 mm (T2) 21.0 mm (T3), 13.8 mm (T4), 27.0 mm (T5), 19.8 mm (T6), at development growth stage five irrigation event 32.4 mm (T1), 23.4 mm (T2), 28.8 mm (T3), 19.2 mm (T4), 36.6 mm (T5), 27.0 mm (T6), at mid growth stage four irrigation event 53.4 mm (T1), 37.2 mm (T2), 48.0 mm (T3), 31.8 mm (T4), 60.6 mm (T5), 44.4 mm (T6), and at late stage two irrigation event 58.0 mm (T1), 40.8 mm (T2), 53.4 mm (T3), 35.4 mm (T4), 67.2 mm (T5), 49.2 mm (T6) applied respectively. The irrigation amount and amount of water added for leaching had no significant difference on onion bulb diameter and bulb length across the years. The highest marketable yield (21784 kg/ha) and water use efficiency (1.89 kg/m3) were recorded at the first year. The maximum bulb diameter were recorded from T6 (5.41 cm) and the lowest recorded from T2 (4.81 cm). Treatment T2 were recommended for the production of onion at middle awash. The developed optimal irrigation scheduling and drainable excess water can be used as a guide to yield potential allocation decision related to soil salinity management.
Key words: Drainage, optimal, leaching, onion.
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