Effect of organic and chemical fertilizers on growth and active constituents of Dodonaea viscosa.

The aim of this study was to investigate the effects of two fertilizers: organic fertilizer (humic acid, HA) at four levels (0, 0.75, 1.5, and 2 mL·L⁻¹) and chemical (NPK 20:20:20) at three levels (0, 0.5, and 1 g per pot). The vegetative growth parameters (plant height, leaf number, branch number, stem diameter, fresh and dry weight) and biochemical characteristics total chlorophyll, nitrogen, phosphorus, and potassium content, protein, and total phenolic acids were analyzed. Foliar application of HA at 2 mL·L⁻¹ + NPK 0.5 g per pot significantly improved the vegetative growth traits (plant height, leaf number, branch number, and stem diameter). The nutrient content (NPK) and protein increased at NPK (1 g per pot). The study also quantified total phenolic compounds and assessed antioxidant activity via DPPH, showing that D. viscosa leaves have high phenolic content and act as a strong natural antioxidant resource. The highest antioxidant activity (85.5 µmol·L⁻¹) was found with the ethyl acetate extract at 200 µmol·L⁻¹. The combination of HA and NPK significantly increased the phenolic acids, especially quercetin, gallic acid, and cinnamic acid. GC-MS identified eleven compounds within the organic layer of the extract, with myrcene (43.431%), eugenol. In conclusion, the optimal HA and NPK combination significantly enhanced vegetative growth, biomass, and secondary metabolite production in Dodonaea viscosa. These outcomes support the hypothesis that combined foliar application of HA and NPK produces synergistic effects on growth and phytochemical biosynthesis.