Optimizing Organic Fertilizer and Planting Density for Enhanced Biomass and Essential Oil Production in Thymus kotschyanus Boiss. & Hohen. Genotypes under Rainfed Cultivation

This study investigated the effects of organic fertilizer (۰ and ۵۰ t/ha farmyard manure) and planting density (۴, ۶, and ۸ plants/m) on biomass production, essential oil (EO) yield, and chemical composition of four Thymus kotschyanus genotypes under rainfed conditions in western Iran over two growing seasons. A factorial split-plot design with three replications was employed. Analysis of variance revealed highly significant effects of genotype, planting density, and their three-way interaction with fertilizer on most measured traits. The medium planting density (۶ plants/m) combined with manure application consistently optimized productivity. The highest fresh biomass (۱۵,۳۲۳ kg/ha), dry biomass (۵,۳۰۸.۸ kg ha⁻¹), and EO yield (۱۸۸.۶ kg/ha) were obtained from genotype ۲ under this optimal treatment. Thymol (۴۸.۹۹–۶۵.۴۴%) and carvacrol (۴.۲۰–۱۰.۹۱%) were the dominant EO constituents. Other major compounds included p-cymene, borneol, α-terpineol, and γ-terpinene, whose concentrations varied significantly with treatments. Pearson correlation analysis indicated strong positive associations among fresh biomass, dry biomass, and EO yield, while major EO components showed reciprocal trends in response to density and fertilizer levels. Principal component and cluster analyses distinctly separate genotypes based on their EO profiles and yield performance. In conclusion, integrating superior genotype selection (genotype ۲) with sustainable organic nutrition and optimized planting density (۶ plants m⁻² with ۵۰ t/ha manure) provides an effective strategy for simultaneously enhancing both the yield and quality of Thymus kotschyanus essential oil under rainfed cultivation systems.

کلیدواژه ها:

farmyard manure ، Rainfed agriculture ، Thymol ، Carvacrol ، Genotype × management interaction