Response of onion (Allium CepaL.) to soil moisture stress condition at different growth stages in the central Highland Vertisols Areas of Ethiopia.

Improving water use efficiency is an important strategy for addressing future water scarcity. Therefore, enhancing agricultural water productivity is a critical response since agriculture is the main consumer of global fresh water. The main objective of this study was to identify sensitive growth stages of onion to soil moisture stress, to determine the critical time for irrigation water application and water use efficiency for onion. The field experiment was conducted for threeconsecutive seasons (2015 – 2017) at main station of Debre Zeit Agricultural Research Center. Fifteen treatments were used. It is arranged by stressing application of the crop water requirement during irrigation event with combinations of four growth stages of onion. All treatments were laid out in randomized complete block design with three replications for each treatment. The result revealed that onion bulb yield and water use efficiency were significantly affected at p< 0.05 bydepriving irrigation water at growth stages among the all treatments. The highest bulb yield (23.8 t/ha) was observed from no stress (control) treatment and followed by stressing at initial (22.7 t/ ha) and at maturity stage (21.6 t/ha) with no statistical difference with control. However, the lowest yield was recorded at stressing all stages of the crop growth period except development (6.7 t/ha). There was also a significant differences of water use efficiency (WUE) detected among the treatments. However, the highest WUE (13.84 kg/m3) had been recorded at stressing all stages except initial. Under irrigated onion production, the mid-stage should be regularly monitored as it significantly affects the yield of onion. Besides, in the areas where irrigation water is limited, limiting the amount of water applied during development and maturity sage is the best solution to enhance water productivity without significantly reducing the bulb yield of irrigatedonion.