From Fruit Waste to Floricultural Resilience: Banana Peel Compost Enhances Salt Stress Tolerance in Zinnia elegans by Improving Soil Fertility, Ion Homeostasis, and Antioxidant Defense

Suitable soil amendments are a prerequisite to overcome the hazardous effects of abiotic stresses such as salt stress (SS). Therefore, the present research evaluated the efficacy of banana peel compost (BPC) as an organic amendment for alleviating salt‐induced phytotoxicity in a commercially important floricultural crop namely zinnia ( Zinnia elegans L. cv Peter Pan). A pot experiment was conducted in a wire house using four SS levels (0, 25, 50, and 100 mM NaCl) with or without the amendment of 2% BPC. Increasing SS significantly reduced plant growth, biomass, leaf area, flower production, and chlorophyll contents, while increased sodium ions (Na ⁺ ) accumulation and disturbed nutrient balance in the soil and plants. In contrast, the BPC application significantly recovered plant growth and physiological performance under SS conditions. The beneficial affects of BPC were more pronounced at moderate and high salinity levels (50 and 100 mM NaCl, respectively), where treated plants maintained greater biomass, leaf area, chlorophyll content, membrane stability, and antioxidant enzyme activities than plants grown in unamended soil. The addition of BPC also reduced the adverse effects of SS on nutrient uptake and osmotic stress, as indicated by lower proline accumulation and improved ionic balance. The BPC application improved soil chemical properties under SS conditions by decreasing electrical conductivity and exchangeable Na ⁺ accumulation while enhancing the availability of K ⁺ , Ca ²⁺ , and Mg ²⁺ . Compared with the unamended treatments, BPC significantly improved ionic balance by lowering Na ⁺ uptake and promoting K ⁺ accumulation in zinnia plants. Overall, the results demonstrate that BPC is an effective amendment for mitigating SS in zinnia while improving soil health and plant performance.