Effects of Organic and Chemical Fertilizers on Leaf Yield, Essential Oil Content and Composition of Lemon Verbena (Lippia citriodora Kunth)

Organic fertilizers with beneficial effects on soil structure and nutrient availability help maintain yield and quality, and they are less costly than synthetic fertilizers. Vermicompost and vermiwash are two organic fertilizers that they contain a biologically active mixture of bacteria, enzymes and phytohormones, also these organic fertilizers can supply the nutritional needs of plants. Lemon verbena (Lippia citriodora Kunth, Verbenaceae) is an evergreen perennial aromatic plant. The lemon-scented essential oil from the lemon verbena has been widely used for its digestive, relaxing, antimalarial and lemony flavor properties. In order to decrease the use of chemical fertilizers for reduction of environmental pollution, this research was undertaken to determine effects of vermicompost and vermiwash in comparison with chemical fertilizer on leaf yield, essential oil content and composition of lemon verbena.
A pot experiment based on a completely randomized design with six treatments and three replications on Lemon verbena was carried out in the experimental greenhouse of the Department of Horticulture Sciences, Tarbiat Modares University, 2012. Treatments consisted of 10, 20 and 30 % by volume of vermicompost and vermiwash (with an addition to irrigation in three steps, including: two weeks after the establishment of plants in pots, the appearing of branches and three weeks before harvest), complete fertilizer and control without any fertilizer. Each replication contained six pots and each pot contained one plant of Lemon verbena provided from Institute of Medicinal Plants, Karaj, therefore 108 pots were used in this experiment. The pots were filled up by a mixture contained 3/5 soil and 2/5 sand (v/v). After three months, plant aerial parts were harvested concomitantly at starting of the flowering stage. Aerial parts were dried at room temperature for 72 hours and dry weights of dried branches and leaves were measured. For isolation of essential oils, about 20 g of dried leaves (three replications of each treatment) was subjected to hydro-distillation for 2 h with a Clevenger apparatus. The extracted essential oils were dried over anhydrous sodium sulphate and then they analyzed by GC and GC/MS. The data were subjected to analysis of variance using SAS software and means compared with Duncan's multiple range test.
The results showed that differences between treated plants with organic fertilizers were not significant for aerial part yield, but leaf yield and essential oil content were affected by fertilizer type (p