Adjusting sowing date to enhance roselle performance and water productivity under water deficiency stress

Climate change induced water scarcity poses a critical challenge to sustainable crop production and an escalating threat to food security, particularly in arid and semi-arid regions Adjusting sowing dates in combination with deficit irrigation to enhance water productivity is a successful adaptation strategy to mitigate the effects of water scarcity on crop production. However, limited information is available on the interactive effects of sowing timing and irrigation levels on roselle (Hibiscus sabdariffa L.) under arid and semi-arid conditions. In this context, a field experiment was conducted during 2021 and 2022 seasons at the AL-Busili Experimental Farm of the Central Laboratory for Agricultural Climate, Agricultural Research Center in Egypt, to assess the effects of three sowing dates (T1: May 19, T2: June 19, and T3: July 19) and three irrigation regimes (I1: 100%, I2: 75%, and I3: 50% of crop evapotranspiration "ETc") on growth performance, yield and water productivity of roselle. The treatments were arranged in a split-plot design with three replications. The results indicated that sowing on June 19 (T2) under full irrigation (100% ETc) significantly increased plant height (253.17 cm), branch number (25.74 plant^- 1), fruit number (100.30 plant^- 1), and sepal dry weight (18.32 g plant^- 1). Deficit irrigation (75% and 50% ETc) enhanced anthocyanin accumulation, with the highest value (52.69 mg g^- 1 DW) recorded under 75% ETc. Notably, the combination of late sowing (July 19) and severe water deficit (50% ETc) achieved the uppermost water productivity, reaching 1.917 and 1.922 kg m^- 3 in the first and second seasons, respectively, despite a reduction in yield. Based on these findings, it could be concluded that the late sowing date can be a viable management strategy in Egypt with limited water availability in terms of water productivity of harvested roselle fruits. These findings highlight a critical comparison between maximizing yield and improving water productivity, suggesting that adjusting sowing date in integration with deficit irrigation can serve as a successful climate adaptation strategy for roselle cultivation in water-limited environments.