EVALUATING THE YIELD REDUCTION OF ONION IN STAGE – BASED DEFICIT IRRIGATION USING DRIP IRRIGATION SYSTEM IN ASKETEMA, NORTHERN ETHIOPIA

Abstract

Recently, irrigation development is on the rise in Ethiopia compared to previous periods. However, outdated and traditional resource utilization and farming methods contribute to food insecurity and instability. Thus, expanding irrigable areas and implementing efficient water management practices are essential to eradicate these problems. In the studied area, onion crop is the important, but, limited crop in the dry season due to irrigation water limitation. Hence, a field experiment was conducted with the objective of evaluating onion crop yield reduction under stage-based deficit irrigation using drip systems by employing three irrigation levels (80%ETc, 90%ETc, and full irrigation 100%ETc) with three replications in a randomized complete block design. The irrigation water scheduling was done using CROPWAT model by fixing the soil moisture depletion as (p=0.3) of total available soil moisture through the growing stages. The water application was monitored and controlled by setting up the irrigation time (T) based on proposed deficit levels. The water level variations were mainly investigated at the two growth stages, vegetative and ripening stages. Statistical analysis revealed that leaf height was not affected by the level of DI while, leaf number, plant height, bulb diameter, marketable bulb yield and total bulb yield had shown significant (P<0.01) differences among DI treatments. The higher water use efficiency of 22.45 kg/m3 was achieved at 90%ETc during ripening stage. The maximum bulb diameter was recorded with the application of full irrigation level in both stages. The highest total bulb yield of 27.38 t/ha was gained at the application of 100%ETc. And minor yield and economic variation was introduced by saving more water at the application of 80%ETc comparing with 90%ETc and full irrigation levels, at the significance probable level of P≤5% in ANOVA. But, the crop response factor (Ky) showed value of (0.65 to 0.87), less than a unit that indicates the onion crop is tolerant for these water stress levels with 11% and 17% yield reduction due to 12.5% and 20% water saved in vegetative & ripening stages respectively. Similarly, the benefit cost ratio values showed a value of greater than a unit. Therefore, for such water scarce areas, the result suggests, employing stage-based deficit irrigation with a drip system, particularly applying 80%ETc, presents a promising approach to enhance water productivity and conservation while maintaining onion crop yield.