Integrated humic acid and vermicomposting changes essential oil quantity, and quality in field-grown Lavandula angustifolia L. intercropped with Brassica nigra L

In recent years, increased environmental concern about the application of synthetic fertilizers for agricultural purposes has resulted in a continuous search for sustainable and environmental-friendly alternatives. However, organic farming systems will not be sustainable without a proper understanding of plant responses and the optimization of these systems. The present study used a two-year factorial design to investigate the effects of the application of humic acid and vermicompost on the essential oil (EO) quantity and quality of Lavandula angustifolia L. intercropped with Brassica nigra L. Results showed that the application of both humic acid and vermicompost increased flower yield (2371.82 kg/ha) by 16.72%, EO content (3.18%) by 22.85%, and EO yield (59.09 kg/ha) by 42.69%. Although the fertilizers were found to be effective even at the lowest rates, the highest flower yield (2522.17 kg/ha), EO content (3.87%), and EO yield (97.61 kg/ha) were observed in the higher rates of humic acid (5000 mg/L) and vermicompost (7.5 t/ha). Forty individual chemical compounds, covering over 98.12% of the compounds, were analyzed by the GC-MS technique from the lavender grown under different treatments. The results demonstrated that the EO chemical profile was affected by the fertilizers and the highest linalool, limonene, and geraniol contents were recorded in the EO samples obtained from the application of 5000 mg/L humic acid and 7.5 t/ha vermicompost. Conversely, the maximum content of geranyl acetate, linalyl acetate, and β-caryophyllene was isolated from the untreated plants. The six constituents listed above accounted for 87.1% of differentiation among treatments based a similarity percentage (SIMPER) analysis. In conclusion, a combination of 5000 mg/L humic acid and 7.5 t/ha vermicompost can be recommended as a valid alternatives to reduce the demand for chemical fertilizers and their environmental hazards in lowly fertile areas.