Foliar Application of Iron and Zinc Affected Aromatic Plants Grown Under Conventional and Organic Agriculture Differently

The utilization of organic fertilizers for the cultivation of wild edible and medicinal plants offers agronomic and ecological benefits, given their suitability to low-input and sustainable production systems. Under such conditions, these species may also benefit from targeted foliar applications of micronutrients to enhance their nutritional quality. This study examined the effects of a vinasse-based organic fertilizer and conventional fertilization regime, in combination with foliar applications of iron (Fe) and zinc (Zn), on the biomass, leaf photochemistry, and plant stress-related responses of Sideritis cypria and Origanum dubium. In S. cypria, organic fertilization resulted in a similar yield compared to conventional fertilization, while O. dubium showed a significant decrease in yield when using organic fertilizers. The impact of spraying with Zn on S. cypria dry matter content was related to the availability of nutrients, particularly nitrogen, while in O. dubium Zn spraying induced a decrease in dry matter. The total phenols content and antioxidant activity of S. cypria were elevated by conventional fertilization and foliar application of Fe, while the combination of organic fertilization and foliar application of Fe and Zn reduced lipid peroxidation. In O. dubium, foliar application of Fe and Zn led to a reduction in total phenols content, antioxidant capacity, and hydrogen peroxide content under adequate nutrition. In general, foliar spraying with Zn tended to improve water use efficiency under specific fertilization practices on both species, while the positive effect of conventional fertilization on nutrient use efficiency still requires further validation. Ultimately, the efficiency of organic fertilization was related to the examined species, inducing variations in leaf chlorophyll content. In addition, foliar application of Fe and Zn affected the antioxidant capacity and mineral content of the examined species. Thus, appropriate fertilization management is vital to fully realize the specific benefits of foliar micronutrient addition.