Effect of Deficit Irrigation Levels at Different Growth Stages on Yield and Water Productivity of Onion (Allium cepa L.) at Raya Azebo Woreda, Northern Ethiopia

The scarcity of water is the most severe constraint for the development of agriculture in arid and semi-arid areas. Under such conditions, the need to use the available water economically and efficiently is unquestionable. The important strategy for increasing water productivity and improving water use efficiency in the area of water scarcity was deficit irrigation. A field experiment was conducted at Mehoni Agricultural Research Center during offseason aimed at investigating the effect of deficit irrigation levels on water productivity of onion (Bombey Red variety) and the most sensitive growth stages of onion crop. The experiment was carried out in split plot design with sixteen treatment combinations and three replications. The treatments include four growth stages (initial, development, bulb formation and maturation) as main plot, and three deficit irrigation levels (80%, 60% and 40% of evapotranspiration of crop (ETc)), and one control irrigation of 100% ETc as subplot. Crop water requirement was estimated using actual daily climatic data. The result showed that deficit irrigation levels, time of deficit irrigation and their interaction had significant (p< 0.01) effect on bulb yield and yield components. The treatment received 100% ETc at the time of development stage gave the highest total bulb yield of 30.67 t/ha with no significant difference from 60% deficit treatments during initial and maturation stages. The result showed that initial and maturation stages were the right time to practicing deficit irrigation without significant yield reduction. Water productivity was the highest with 60% deficit irrigation at maturation stage (8.96 kg/m3), and 0.17ha additional area to be irrigated by saved water. The yield response factor (Ky) was higher (1.98) when 40% deficit occurred at development stage. The result revealed that onion bulb yield was most sensitive to water deficit that occurred at development and bulb formation stages. While maximum yield was obtained when the whole crop water requirement was applied, implementing deficit irrigation at appropriate stage could increase the irrigated area as a result of high water productivity.

水资源短缺是干旱和半干旱地区农业发展最严峻的制约因素。在此条件下，经济高效地利用现有水资源的必要性毋庸置疑。在水资源短缺地区，提高水分生产率和用水效率的重要策略是亏缺灌溉（deficit irrigation）。为探究亏缺灌溉水平对洋葱（Bombey Red品种）水分生产率及作物最敏感生育期的影响，在Mehoni农业研究中心的非生长季开展了田间试验。试验采用裂区设计，共设16个处理组合，重复3次。主区为4个生育期（初始期、发育期、鳞茎形成期、成熟期），副区为3个亏缺灌溉水平（作物蒸散量（ETc）的80%、60%、40%）及1个对照处理（100% ETc）。作物需水量采用实际日气候数据估算。结果表明，亏缺灌溉水平、亏缺时期及其交互作用对鳞茎产量及产量构成因素均有极显著（p<0.01）影响。发育期采用100% ETc处理的总鳞茎产量最高，达30.67吨/公顷，与初始期和成熟期采用60%亏缺处理的产量无显著差异。结果表明，初始期和成熟期是实施亏缺灌溉且不显著降低产量的适宜时期。成熟期采用60%亏缺灌溉的水分生产率最高（8.96千克/立方米），且节约的水量可额外灌溉0.17公顷土地。发育期实施40%亏缺时，产量响应因子（Ky）较高（1.98）。结果显示，洋葱鳞茎产量对发育期和鳞茎形成期的水分亏缺最为敏感。尽管满足全生育期作物需水量可获得最高产量，但在适宜时期实施亏缺灌溉可通过提高水分生产率增加灌溉面积。