1. Introduction: Celery (Apium graveolens L.) is a high-value vegetable belonging to the Apiaceae family, widely consumed for its long, fibrous petioles and nutrient-rich leaves. Calcium (Ca) is an essential macronutrient that plays a fundamental role in maintaining cell wall stability, membrane integrity, and determining overall postharvest quality. While plant roots can absorb calcium from the soil, the low mobility of Ca within the plant’s vascular system often leads to localized deficiencies, particularly in younger, rapidly growing tissues with low transpiration rates. Such deficiencies frequently manifest as physiological disorders like black heart. Foliar application of soluble calcium salts has emerged as a highly effective alternative to overcome soil-to-shoot transport limitations. However, the efficacy of this method is significantly influenced by the chemical source and the specific dosage applied. To our knowledge, research comparing the effectiveness of various calcium sources specifically on celery remains limited. Therefore, this study was conducted to investigate the influence of different foliar calcium sources and concentrations on the growth, yield, and quality attributes of celery.
2. Materials and Methods: The experiment was conducted as a randomized complete block design with three replications to evaluate the effects of various calcium sources on celery growth, yield, and quality. The treatments included different concentrations of calcium nitrate (Ca(NO₃)₂; 10 and 15 g L⁻¹), calcium chloride (CaCl₂; 5 and 10 g L⁻¹), and calcium lactate (C6H10CaO6; 1 and 2 g L⁻¹). Foliar sprays were applied at the 5th–6th true leaf stage and repeated three times at 15-day intervals using a mechanical mist sprayer to ensure uniform coverage—distilled water served as the control. Standard agronomic practices, including weed management, were strictly carried out in accordance with the recommended package of practices throughout the entire crop growth cycle. Key parameters measured included plant height, petiole length, leaf number per plant, total plant yield, total chlorophyll content, carotenoid content, ascorbic acid (vitamin C), total phenols, and flavonoid contents. Additionally, the incidence and severity of physiological disorder symptoms (black heart and petiole pithiness) and Ca concentrations in both internal and external leaves were recorded. Data were subjected to analysis of variance (ANOVA) using SAS statistical software, and treatment means were compared using Duncan’s multiple range test at P=0.05.
3. Results and Discussion: The results demonstrated that foliar application of various calcium sources significantly enhanced the growth and quality parameters of celery compared to the control. The highest plant height (67.33 cm), petiole length (30.3 cm), leaf number per plant (25.26), and total plant yield (91,110 kg ha⁻¹) were significantly achieved through the application of 10 g L⁻¹ CaCl₂, representing a substantial improvement over the control plants. The superior performance of CaCl₂ at this concentration may be attributed to the high solubility of the chloride form and its specific role in promoting leaf expansion and cellular turgor. Furthermore, the chloride ion may also contribute to better osmotic adjustment within the petiole tissues, which is essential for rapid vegetative growth in celery. Regarding biochemical quality, the foliar application of 15 g L⁻¹ Ca(NO₃)₂ resulted in the maximum concentrations of total chlorophyll (2.87 mg g⁻¹ FW), carotenoids (0.72 mg g⁻¹ FW), and total phenols (40.7 mg 100g⁻¹ FW), alongside the highest calcium accumulation in internal leaves (4.04). The synergistic effect of nitrate and calcium in this treatment likely facilitates better nitrogen assimilation, which is a precursor for chlorophyll biosynthesis and protein synthesis. The increase in phenolic compounds and flavonoids suggests that calcium application triggers secondary metabolic pathways, thereby improving the overall nutritional profile of the plant. Furthermore, the highest ascorbic acid (vitamin C) content was observed in plants treated with both 15 g L⁻¹ Ca(NO₃)₂ and 10 g L⁻¹ CaCl₂, indicating that these specific sources effectively boost the antioxidant capacity of the plant. Crucially, the foliar treatments significantly mitigated physiological disorders, specifically black heart and petiole pithiness, by ensuring higher calcium availability in the leaf tissues. This reduction in disorder symptoms is attributed to the role of Ca²⁺ in stabilizing cell membranes and reinforcing the structural integrity of the cell walls, which prevents the collapse of tissues during rapid growth. Since black heart is a classic calcium-deficiency disorder, the localized foliar delivery of calcium effectively bypasses the limited xylem mobility of Ca, ensuring that the rapidly expanding central leaves receive adequate nutritional support. The observed increase in antioxidant compounds suggests that calcium plays a critical role in modulating metabolic processes and enhancing the plant’s defense mechanisms against oxidative stress and enzymatic degradation. Thus, the synergy between calcium uptake and the activation of metabolic pathways contributes to both improved yield and superior nutritional quality.
4. Conclusion: In conclusion, foliar application of calcium is an effective, practical strategy for improving celery performance. Specifically, the use of 15 g L⁻¹ Ca(NO₃)₂ is recommended for maximizing chlorophyll, phenolic, and antioxidant content, while 10 g L⁻¹ CaCl₂ is most effective for enhancing vegetative growth and total yield. Both treatments are highly efficient in reducing common physiological disorders such as black heart and petiole pithiness, thereby improving the overall commercial value of the crop. Future studies should focus on the economic feasibility and long-term storage quality of celery treated with these calcium sources.