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.
