Effects of terminal drought stress and harvesting time on seed yield and essential oil content of fennel (Foeniculum vulgare Mill.)

To study the changes of yield and essential oil of fennel (Foeniculum vulgare Mill.) under drought stress condition and different harvesting times, a field experiment was conducted at College of Agriculture, University of Zanjan in the spring of 2011. The experiment was conducted as a split plot based on complete randomized block design with three replications. In this study, the effects of water stress in three levels including control, drought stress at flowering and grain filling stages were assigned to the main plots and three harvesting times including harvest at soft dough (58% moisture content of grain), hard dough (37% moisture content of grain) and maturity stages (16 % moisture content of grain) were assigned to the sub plots. Results showed that the effect of drought stress on grain and essential oil yield, grain essential oil content, 1000-grain weight, number of umbellet in umbrella, number of grain in umbellet, number of grain in umbrella was significant (p ≤ 0.05). Majority of mentioned traits decreased significantly (p ≤ 0.05) under drought stress condition. Therefore, the highest grain yield (1436.63 kg/ha) and essential oil yield (34.54 kg/ha) were obtained in control treatment (full irrigation) and the lowest amounts of mentioned traits were obtained in drought stress at grain filling stage. According to the obtained results, the effect of harvest time on grain and essential oil yield, grain essential oil content, 1000-grain weight, number of grain in umbellet and number of grain in umbrella, was significant (p≤0.01). Therefore, the highest and lowest grain yield (1425.75 and 784.81 kg/ha) was obtained in hard dough and maturity stages, respectively. In addition, the highest essential oil yield (33.97 kg/ha) was obtained in hard dough stage but there was no significant difference about essential oil yield between hard dough and maturity stages. It can be concluded that the fennel plant is sensitive to drought stress at reproductive growth stages and the quantity and quality of fennel yield can be affected by harvest time.