Yassin Soliman, Wagdi Saber Soliman, Ahmed M. Abbas, Stephen J. Novak
Sweet basil (Ocimum basilicum L.) is a member of the Lamiaceae family, which includes a wide variety of medicinal and aromatic herbs cultivated for their essential oils and bioactive compounds. However, prolonged drought stress can significantly impair growth and essential oil content. In this study, a two-season pot experiment was conducted under open-field conditions. The study was carried out at the Floricultural Nursery, Faculty of Agriculture and Natural Resources, Aswan University, Egypt, during 2024 and 2025, with the aim of assessing how foliar applications of silicon (Si) and zinc (Zn) impact the morphological, physiological, and biochemical responses of sweet basil under different soil water capacity (SWC) levels (80%, 60%, and 40% SWC). Drought stress markedly reduced plant height, branch number, leaf area, biomass, photosynthetic pigments, macronutrient content, and essential oil content, while increasing levels of proline and secondary metabolites such as phenolics, flavonoids, and ascorbic acid. Growth and productivity were highest under 80% SWC, followed by 60%, and lowest under 40%. Under drought stress (40% SWC), Si200 increased plant dry biomass by approximately 12%, chlorophyll content by 53%, and essential oil content by 46% compared with untreated plants. Silicon application proved more effective at ameliorating the negative consequences of drought than Zn, with Si200 combined with 80% SWC yielding the best results in terms of plant performance and essential oil percentage and content. Meanwhile, Si200 under 40% SWC induced the highest accumulation of secondary metabolites. These results highlight the potential of silicon foliar application as a practical strategy to reduce drought stress in sweet basil, enhancing both yield and phytochemical quality, and offering valuable guidance for sustainable cultivation under water-limited conditions.