An excessive amount of chromium in soil has detrimental effects on plant processes, and impairs food security, and public health. The application of nanoparticles may be a suitable solution and an innovative strategy by which to reduce plant abiotic stresses and pollution in the agricultural ecosystems. This research focuses on the effects of chitosan nanoparticles (CS-NPs) on thyme (Thymus vulgaris L.) plants grown in Cr-contaminated soil. The effects of CS-NPs as a soil amendment at four concentrations were investigated on plant nutrient uptake, photosynthesis parameters, antioxidant system, and essential oil (EO) content under soil Cr stress. The results show that chromium stress reduced fresh and dry weight of shoots, the uptake of macro-, and micro-elements, chlorophyll and carotenoids. The application of CS-NPs improved the antioxidant enzyme activity, reduced malondialdehyde, and increased the content of nutrients, EOs, photosynthetic pigments, and chlorophyll fluorescence parameters. The intermediate dose of chitosan nanoparticles (0.1% w/v) best valorized the content and yield of thyme EOs under chromium stress. These results are indicative that the application of CS-NPs can represent a supportive approach for plant production in soils contaminated with heavy metals.

Nowadays, the application of sustainable and eco-friendly fertilizers plays an important role in improving the essential oil (EO) quantity and quality of medicinal and aromatic plants. Hence, the study aimed to investigate the effects of green manures, organic manures and biofertilizers on the nutrient content, dry matter yield, EO productivity and quality of peppermint. The treatments included green manures [barley monoculture (Bm), hairy vetch monoculture (HVm) and replacement intercropping of 75%HV + 25%B, 50%HV + 50%B and 25%HV + 75%B], arbuscular mycorrhizal fungi (AMF) and vermicompost (VC). A 50%HV + 50%B green manure appears to be the most effective treatment, since it provides the greatest amount of nutrients (N and K, 18.8 g kg⁻¹, and 18.1 g kg⁻¹, respectively), the tallest plants (61.5 cm), the most nodes per plant (17.5), the lateral branches (24.4), the highest leaf greenness index (45.5) and dry yield (266.7 g m⁻²) in peppermint. Moreover, this treatment evidenced the larger EO content (1.8%) and EO yield (4.84 g m⁻²). Regardless of the treatments, the chemical composition of peppermint EO was characterized by menthol (32.35–37.73%), menthone (16.96–20.64%) and 1,8-cineole (6.18–7.78%). The maximum content of menthol and 1,8-cineole was obtained by the application of 50%HV + 50%B. Additionally, the highest content of menthone was observed in AMF treatment. These results indicate that the application of 50%HV + 50%B green manures could be suggested as an environmentally friendly strategy for improving EO quantity and quality of peppermint.