https://doi.org/10.37229/fsa.fja.2026.10.10

One of Egypt's biggest obstacles to sustainable agriculture is the lack of water. By assessing the effects of applying biochar composite (BC) which consists of biochar made from a mixture of wood (produced from woody ornamental nursery wastes) and biochar made from banana waste at a 2:1 (w/w) ratio either alone or in conjunction with tripartite microbial consortium comprising pure, active strains of Azotobacter chroococcum, Azospirillum lipoferum, and Bacillus polymyxa as plant growth promoters (PGPR), this study investigated sustainable methods to reduce water stress in Calendula (Calendula officinalis L.). During the growing seasons of 2023/2024 and 2024/2025, two factorial field experiments with a split-plot design were carried out at the Medicinal Plant Farm, Faculty of Pharmacy, Cairo University, Giza, Egypt. Three irrigation schedules were applied to calendula plants: normal (14-day intervals; I1), moderate water deficit (21-day intervals; I2), and severe water deficit (28-day intervals; I3). The most effective regime, according to the results, was the 21-day irrigation interval, which saved 16% to 21% of irrigation water without affecting the calendula plants' vegetative development, flowering, or chemical analysis. Co-application of Biochar composite (BC) and Plant Growth-Promoting Rhizobacteria PGPR demonstrated the best biological synergy under this mild stress. When compared to the untreated control, this combined treatment greatly improved vegetative growth, flowering characteristics, total carotenoids and total flavonoids, total chlorophyll (a and b), total carbohydrates, and nutritional levels (N, P, and K). Additionally, it maintained relative water content (RWC%), accumulated proline and phenolic contents, and increased phytohormones, antioxidant enzymes, and water productivity all of which substantially mitigated yield losses caused by drought. The co-application of Biochar composite (BC) and PGPR treatment under moderate water shortage (21-day intervals) might be suggested as a sustainable agronomic strategy to enhance vegetative growth, essential oil composition, and nutritional quality of Calendula plants based on the obtained results.