AbstractUnder arid and semi-arid climates, adopting the appropriate tools for alleviating water deficit impacts is a critical factor that affects the physiological characteristics and yield of sunflower. Therefore, in order to find promising field practices in sunflower cultivation, the strip plots design in randomized complete block arrangement was used to examine the effects of two irrigation regimes as 100% (FI) and 85% (DI) of crop evapotranspiration and five antioxidant treatments on physiological and agronomic traits, yield response factor, and irrigation water use efficiency (IWUE) of sunflower. The antioxidant treatments involved two rates of ascorbic acid (150 and 300 mg L⁻¹) and two rates of citric acid (250 and 500 mg L⁻¹), in addition to the check treatment (tap water). The study was conducted for two growing seasons of 2019 and 2020 at the Experimental Farm of Ain Shams University, Egypt, located in a semi-arid environment. Findings showed that exogenous application of higher rate of ascorbic acid, i.e. 300 mg L⁻¹ with FI exhibited the highest increase of chlorophyll a, chlorophyll b and the lowest proline content compared to other interaction treatments. Seed yield was significantly higher with FI plus ascorbic acid 300 mg L⁻¹ and DI plus ascorbic acid 300 mg L⁻¹ treatments than with their counterpart check treatment in both growing seasons. Under DI, IWUE was improved with antioxidant-treated plants compared to untreated plants. Yield response factor as an indicator of crop tolerance to drought was higher than the unit (> 1) under all ascorbic acid and citric acid levels. It could be concluded that ascorbic acid and citric acids partially mitigated the reductions in growth and yield caused by low water supply. However, yield response factor demonstrated that the crop is still sensitive to drought. Thus, other applicable patterns should be adopted to increase the yield potential of sunflower for counteracting the adverse impacts of drought.