Influence of fennel development stage on herbage and essential oil yield.

European pharmacopoeia distinguishes two varieties of Foeniculum vulgare ssp. capillaceum: vulgare and dulce, differing in the content of main essential oil components. Considering the biological aspect, var. dulce does not over-winter in the continental areas. The aim of the investigation was to determine the effect of fennel development stages on the fresh herbage yield, and essential oil yield and components. Mineral fertilization was the same for both cultivars. Quality parameters of essential oil were analysed by GC-MS method. It was found out that the crop of var. vulgare can be cut three-times a year in the stage H (herbage before blooming), twice in the stage B (herbage in the full bloom), and once a year in the stages M and W (milky and wax maturity of seed), since var. dulce can be cut twice a year only in the stage H. In all observed stages of plant development var. vulgare gave higher yields of fresh biomass (109, 156, 129 and 140 %) and essential oil (199, 405, 304 i 614 %) compared to var. dulce in the first growing season (crops of equal age). As a two-year old crop, var. vulgare yielded about 150 % of yields achieved in the first year of cultivation. The highest yield of essential oil (38.5 g•m-2), besides the lowest herbage yield (2.07 kg•m-2), was achieved by one-fold harvest in the stage M of var. vulgare. The essential oil main component in both varieties is anethol, followed by fenchone and α-pinene in vulgare, and limonene in dulce. During the vegetation period, a rate of anethol and fenchone increased, while the rate of α-pinene and limonene decreased. Plant growth and development was weak in the drought condition (dulce, the second growing season), and the crop was severely damaged by cold winter (vulgare, second over-wintering).