Investigating the effects of different planting bed on vegetative characteristics and essential oil components changes over the years of growth in Satureja mutica Fisch. & C.A. Mey. under rainfed condition

Awareness of changes in medicinal plant yield quantity and quality over time is one of the most important goals in agricultural management. Satureja mutica is one of the valuable medicinal species growing in Iran. This study was conducted to evaluate the effects of different planting beds on changes in vegetative characteristics and essential oil components over the years of growth in S. mutica under rainfed conditions. The experiment was conducted in the form of split plots in a randomized complete block design for three years (2018-2020) in the rainy conditions of Feridounshahr city, Isfahan province. Planting beds as the main plot included cow manure (30 tons per hectare), wheat straw (10 tons per hectare), and control (without cow manure and wheat straw). After the preparation of the field, the seedlings were planted at the bottom of the wells created at a distance of 50 x 50 cm from each other. During the growing season and at the time of 50% flowering, the studied traits including total plant dry weight, leaf and stem dry weight, plant height, crown diameter per plant, canopy area per plant, and in each square meter of land and the number of stems per plant were measured. For essential oil extraction, the flowering branches of the plants were harvested at the full flowering stage. After drying in the shade, the essential oil was extracted by the water distillation method. After determining the yield of essential oils based on the dry weight of the plant, the essential oils were analyzed and identified by gas chromatography, and gas chromatography was connected to a mass spectrometer in the phytochemistry laboratory of the Research Institute of Forests and Rangelands. Considering that the plant is several years old and measurements are carried out every year on fixed plots, the design analysis was done on divided plots at the time of implementation. The SAS computer program was used to perform statistical calculations, and the LSD test was applied to compare the means. For essential oil extraction, the flowering branch of the plant was harvested at the full flowering stage. After drying in the shade, the essential oil was extracted by the water distillation method. After determining the yield of essential oils based on the dry weight of the plant, the essential oils were analyzed and identified by gas chromatography, and gas chromatography was connected to a mass spectrometer in the phytochemistry laboratory of the Research Institute of Forests and Pastures. The SAS computer program was used to perform statistical calculations, and the LSD test was used to compare the means. The variance analysis of the data showed that the effects of bed, year, and their interaction effects on the measured traits were significant in many cases. Results showed that the highest values of plant height, crown diameter, canopy area, and number of stems per plant in the first year were seen in manure treatment. In the last year, they were in control. The highest rates of total dry weight, leaf dry weight, essential oil yield, and essential oil percentage were observed in control in the last year. These rates were 1427, 891, 42 kg ha-1, and 4.67%, respectively. The main essential oil components are thymol, carvacrol, p-cymene, and gamma-terpinene. These essential oil components are affected by the planting bed and the growth year. So in the case of p-cymene, the highest amount obtained in the first year was in the straw treatment. The highest amounts of gamma-terpinene were observed in all three planting bed treatments in the last year of growth. S. mutica had significant amounts of thymol, and the trend of changes among planting bed treatments and during growing years was very small. The highest amounts of carvacrol were observed in straw treatment and animal manure in the second year of growth. The results of the correlation coefficients showed that the most vital traits affecting essential oil yield were total dry weight, leaf and stem, and essential oil percentage. Thymol and p-cymene were inversely correlated with carvacrol and gamma-terpinene. On the whole, to produce S. mutica under rainfed conditions similar to this study, manure or straw could affect yield and essential oil over the first and second years; however, in the third year, this effect diminished, and control treatment was superior to straw and manure treatments.