Influence of Nitrogen Fertilizers on the Yield and Composition of Thyme (Thymus vulgaris)

Abstract

The influence of nitrogen fertilizers on the yield of crop, as well as on the production and composition of the essential oil and some other chemical characteristics of thyme, was investigated. Different levels of fertilizers (N = 0, 45, 90, and 135 kg ha^-1) were applied. It was found that fertilizers increase thyme crop, but differences in the yield of essential oil were not remarkable. However, the use of certain amounts of nitrogen fertilizers resulted in higher yields of essential oil obtainable from the cultivation area unit (dm³ ha^-1). Totally, 61 constituents were identified in thyme essential oil by capillary GC and GC-MS. Thymol was the dominating compound in the all analyzed oils (44.4−58.1%), followed by p-cymene (9.1−18.5%), γ-terpinene (6.9−18.9%), and carvacrol (2.4−4.2%). Differences in the percentage of these and other compounds in thyme herb cultivated under different fertilization doses were not significant; very slight changes in the percentage composition were detected after drying. Some variations in the amount of individual constituents expressed in arbitrary units per kilogram of herb (which is almost equivalent to mg kg^-1) were observed. The highest amounts of sugars and sucrose, in particular, were determined in the second year of thyme cultivation. Differences in the content of dry soluble substances were not meaningful, and there was no effect of nitrogen fertilizers on this chemical characteristic. Some effect of fertilization on the content of vitamin C and carotenes was observed in the first year of thyme cultivation. It was determined that nitrogen fertilizers influence the amount of nitrates, which was highest in the second-year−first-harvest. Keywords: Thyme; Thymus vulgaris; Labiatae; nitrogen fertilizers; chemical composition; essential oil; yield