Effects of vermicompost on amount of quercetin, oleuropein, and leaf elements

Olive (Olea europaea L.) is a valuable medicinal tree in addition to being used as a food. Olive leaf, as an organ containing active ingredients, is of great value in various industries. Use of olive leaves extract as a natural antioxidant is one of the most common applications of this plant. Oleuropein is the most important phenolic compound in olive species that plays an important role in health. Oleuropein and quercetin are used as effective compounds in anti-cancer, anti-virus, and anti-inflammatory drugs. To investigate the effects of vermicompost (0, 1, 2, 3, and 4 tons per hectare) application on morphological traits, leaf yield, and oleuropein, quercetin, macro and micro elements of the olive leaf extract under field conditions, an experiment was conducted in a randomized complete block design with three replications (nine shrubs in each replicate) at the Alborz Research Station, Research Institute of Forests and Rangelands in two years. Three-year-old shrubs were planted at a distance of 5 m on the row and 5 m between the rows at a depth of 50 cm. Vermicompost affected fresh and dry leaf yield per hectare and quercetin and oleuropein amounts of the leaves significantly (at the level of 1% probability) in both years. The highest dry leaf yield per hectare was obtained in the 4 tons of vermicompost treatment (55.573 kg in the first year and 63.047 kg in the second one). The amount of quercetin increased from 18.48 and 18.7 µg.mg-1 dry matter in the control treatment (in the first and second years, respectively) to 34.67 and 37.7 µg.mg-1 dry matter in the 4 tons vermicompost per hectare treatment (in the first and second years, respectively). Also, the use of 2 tons of vermicompost per hectare increased the leaf oleuropein in both years. Different vermicompost treatments increased the uptake of most macro and micro elements including phosphorus, calcium, magnesium, iron, manganese, zinc, and copper in both years. The results showed that the appropriate amounts of vermicompostcould be used to produce a plant with high quercetin and oleuropein.