Effect of Organic Manure and Plant Growth Promoting Microbes on Yield, Quality and Essential Oil Constituents of Fennel Bulb (Foeniculum vulgare Mill.)

Bulb fennel (Foeniculum vulgare Mill.) has gained importance for its high-value bulb production. A field experiment was conducted in a farm in El-Santa, Ghatbia, Egypt, to enhance productivity and quality attributes of E vulgare bulbs using different fertilizers: biofertilizer. organic fertilizer (rabbit manure). and mineral fertilizer [nitrogen (N), phosphorus (P), and potassium (K)]. The biofertilizers included nitrogen fixer bacteria (Azos), phosphate solubilizing bacteria (Bin). and potassium solubilizing bacteria (Bc) with/without vesicular arbuscular mycorrhizal (VAM) fungi. Application of NPK at 150% of the RD and rabbit manure at 60 m(3)/fed resulted in the highest values of branch number, bulb weight, bulb yield, percentages of total carbohydrates, N, P, and K, as well as features of marketable bulbs including firmness. total soluble solids, titratable acidity, vitamin C, and bulb essential oil. Moreover, the GC/MS analyses of bulb essential oil of the organically and chemically fertilized plants showed the increase of trans-anethole, the predominant constituent responsible for bulb's flavor. However, the highest proportion of estragole (9.65%), an undesirable compound, was recorded with 150% of recommended NPK. In comparison, the lowest estragole content (4.09% and 5.64%) was obtained by organic fertilizer (rabbit manure at 60 m(3)/fed) and biofertilizer (Azos+Bin+Bc+VAM), respectively. The increase in bulb yield (11.76-11.99 ton/fed) and essential oil content (0.076-0.080%) of bulbs obtained with organic manure (rabbit manure at 60 m(3)/fed) was accompanied by a marked decrease in estragole and an increase in the most important constituents, alpha-pinene. beta-pinene, liinonene, trans-anethole, and anisaldehyde. Hence, the organic fennel bulb can be produced with an abundant and high-quality crop which consolidates the concept of ecological and organic farming for this important crop.

Automated summary

This study aimed to enhance the productivity and quality attributes of bulb fennel through the use of different fertilizers. The results showed that the application of organic fertilizer and biofertilizer led to higher bulb yield and nutritional value, while reducing the content of undesirable compounds like estragole.