Exogenous Humic Acid and Magnesium Nanoparticles Synergistically Improve Growth, Photosynthesis, Protein, and Glycosides of Stevia (Stevia rebaudiana Bertoni)

There is considerable amount of interest in using organic compounds and metallic nanoparticles to improve plant performance. Although humic acid (HA) and magnesium nanoparticles (Mg NPs) have been used alone in certain plants or in conjunction with other compounds, the exact function of this combination is unknown. This study aimed to evaluate the effects of humic acid and magnesium nanoparticles separately and in combination with respect to growth, chlorophyll quality, protein, and various glycoside kinds of stevia (Stevia rebaudiana Bertoni). The experiment was conducted with humic acid (1 and 2 g/L) and magnesium nanoparticles (0.1 and 0.2 g/L). The results showed that combined humic acid (2 g/L) and magnesium nanoparticles (0.2 g/L) significantly increased plant height (20%), number of branches (54%), biological yield (39%), leaf magnesium content (43%), soluble protein content (61%), total chlorophyll (154%), and SPAD value (30%). Additionally, this treatment enhanced the yields of rebaudioside A (71%), rebaudioside B (99%), rebaudioside C (108%), stevioside (172%), dulcoside (161%), and total glycosides (123%). The co-application of humic acid at 2 g/L and magnesium nanoparticles at 0.2 g/L can be recommended for improving growth and enhancing the quality and quantity of glycosides, which can be beneficial for agriculture and food sciences.