Influence of Sowing Date and Foliar Application of Humic Acid on Yield and Volatile Oil of Sweet Fennel (Foeniculum vulgare) Plants

A field trial was conducted to assess the effect of humic acid concentrations (0, 1.5, 3.0 and 4.5 g/l) on growth, yield and volatile oil constituents of fennel sown on 15th October, 1st November and 15th November during the two successive seasons of 2017/2018 and 2018/2019. The earliest date (15th October) recorded the best results regarding all fennel growth, yield and fruit constituents of volatile oil yield. Foliar application of humic acid in high concentration (4.5 g/ml) showed significant impact on plant height, branch number/plant, stem diameter, number of umbels/plant, fruit yield/plant, total fruit yield/feddan, volatile oil percentage, volatile oil/plant and volatile oil/feddan during both seasons. Volatile oil of fruits collected from plants sown in mid-October induced the highest percentage of anethole (74.96 %) and the lowest percentage of estragole (15.37%) in comparison with the plants sown in the beginning and middle November. The higher concentration of humic acid increased the percentage of anethole comparing with other concentrations. The foliar application by humic acid in high concentration of fennel sown in mid-October seems to be the best combination for getting higher fruit yield and high quality of volatile oil.