Improvement of production and quality of secondary metabolites in thyme (Thymus daenensis Celak) through eco-friendly fertilizers

Exploring the link between manure levels and the harvests of medicinal plants is vital for essential oil yield. This research aimed to assess how various manure types and application rates affect thyme growth and its volatile oils. The experimental treatments included various rates (100, 143, and 250 kg N ha−1; labeled DL, DM, DH) of poultry manure (P), sheep manure (S) and cattle manure (C), along with chemical fertilizer (C-F) and a control. Results showed that the highest chlorophyll-b level was found with the P-DH treatment. In the first cutting (cut1), biomass for plants treated with P-DH, S-DM, and S-DH was significantly higher than that of the C-F treatment. Essential oil (TEO) yields from medium and high levels of sheep and poultry manures exceeded those from C-F in cut1, while only the P-DH and S-DH treatments showed a significant edge over C-F in the second cutting (cut2). Antioxidant capacity was acceptable for C-DL and C-DM in the cu1, while P-DH, C-DH, and S-DH showed adequate antioxidant capacity in the cut2. In summary, the first cutting favored thymol production, particularly under sheep manure treatment, while the second cutting was better for optimizing TEO yield, especially with higher levels of poultry manure.