Application of graphene oxide nanoparticles for improvement of growth parameters, photosynthetic pigments, and essential oil quality and yield of Lavandula angustifolia Mill. under green manure incorporation

Increasing chemical fertilizer usage in agroecosystems is a serious concern that requires continuous attention. In this regard, a field experiment was performed to evaluate the effect of graphene oxide nanoparticles (GO-NPs) on lavender (Lavandula angustifolia Mill.) under different fertilizer sources of green manure (GM). A factorial experiment was conducted using a randomized complete block design with three replications. The first factor was the application of GM in three levels: without GM, with hairy vetch, and with bitter vetch. The second factor was the foliar application of GO-NPs at four levels: control (distilled water), 12, 25, and 50 mg L−1. The optimal treatment combination for enhancing lavender growth and essential oil (EO) production was foliar application of 50 mg L⁻¹ GO-NPs with hairy vetch GM. Plant height, inflorescence length, photosynthetic pigments, essential oil content, and essential oil yield were improved, as well as the macro- and micronutrient content of lavender plants that were increased using GO-NPs foliar spraying and manure application. Total protein and carbohydrate contents increased significantly in plants treated with foliar application of 50 mg L−1 GO-NPs and hairy vetch GM. Also, foliar application of 25 mg L−1 GO-NPs in combination with hairy vetch considerably enhanced dry and fresh matter yield. Foliar application of GO-NPs and GM significantly increased the content of EO components (e.g., borneol, Linalool, 1,8-cineole, and linalyl acetate) in treated plants compared to the control. The highest and the lowest percentages of borneol were recorded in lavender plants under bitter vetch GM with 50 mg L−1 of GO-NPs and untreated plants, respectively. Overall, the results of this experiment demonstrate that the combined application of hairy vetch (as GM) and GO-NPs can serve as an effective alternative to chemical inputs, while also enhancing lavender growth parameters and improving both the quantity and quality of its EO.