The Yield and Composition of Dill Essential Oil in Relation to N Application, Season of Cultivation and Stage of Harvest

Abstract

The effect of nitrogen (N) fertilization, season of cultivation and stage of harvest on the growth, foliar essential oil composition and yield of dill (Anethum graveolens L. cv. Ducat) was studied in two consecutive crops. Seeds were sown in October (autumn-winter crop) and January (spring crop) and the plants transplanted to a substrate of peat and perlite (1:1 v/v) 30 and 39 days later, respectively. Nitrogen (NH4NO3) was applied weekly at four levels (50, 150, 300, 450 ppm) in a completely randomized design. The plants were harvested at 158 (autumn-winter crop) and 83 (spring crop) days after sowing. The plant foliage was weighed and the essential oils were isolated by hydro-distillation and analyzed by GC/MS. The foliage fresh weight per plant progressively increased with increasing N up to 450 ppm in the autumn/winter, but was maximal at 300 ppm N in the spring. The essential oil concentration within the foliage was low and was unaffected by N application in the autumn/winter, but was significantly higher at 300 ppm N than at other N levels in the spring. The main components of the foliar essential oil were α-phellandrene, β-phellandrene, dill ether, α-pinene, β-pinene, α-thujene, myrcene, and π-cymene. In both crops α-phellandrene was the principal constituent. In the spring the concentration of all the essential oil constituents identified (except π- cymene) was highest at 300 ppm N, whereas in the autumn/winter crop the concentrations of α-phellandrene, β-phellandrene and dill ether were also higher at 300 ppm N, but the other constituents were not affected by higher N. It is concluded that for the autumn/winter crop 450 ppm N is optimal for biomass and foliar oil yield (biomass x oil concentration) whereas in the spring 300 ppm N is recommended.