Enhancement of phenoilc compounds of olive (Olea europaea L.) leaf with soil application of chemical and organic fertilizers

Olive tree (Olea europaea L.) leaves are a very promising and unique herbs source which have considerable therapeutic applications. Olive leaves contain high amounts of phenolic compounds such as phenolic acids, flavonoids, phenylpropanoids and secoiridoids. Oleuropein (secoiridoid compound) is considered as the main active phenolic compound in olive leaves. Fewer studies are dedicated to the effects of fertilization on the chemical composition of olive leaves. Therefore, the current study aimed to investigate the associated changes in morphological characteristics, mineral profile and oleuropein and quercetin contents in olive leaves fertilized with chemical and organic fertilizers.

In order to evaluate the effect of different treatments of chemical and organic fertilizers (humic and fluvic acid) on morphological characteristics, macro- and micronutrient elements as well as phenolic compounds (oleuropin and quercetin) of Zard cultivar, two separate experiments were conducted in a randomized complete block design with three replications in the 2013 crop year. The treatments included application of five levels of NPK (0, 50, 100, 150 and 200 kg ha-1) and six levels of humic acid and fluvic acid (0, 5, 7, 10, 12.5 and 15 liters ha-1).

The results of chemical fertilizers showed that the highest plant height (117.7 cm) and branches number (34 branches) showed in N200P200K200 and N100P100K100 kg ha-1, respectively. The most leaves (60 leaves) were obtained in application of 10 liters per hectare of organic fertilizers. Compared to the control, application of 100 and 200 kg ha-1 NPK showed an increase of 30 and 80% of the oleuropine and quercetin content, respectively. The effect of organic fertilizers was only significant on quercetin content, and its maximum (397.7 μg g-1) was measured in 10 g liters-1 treatment. Effect of chemical fertilizer levels on all measured macro- and micronutrients except potassium was significant and the highest measured values of the elements were obtained at N200P200K200 kg ha-1 level. The effect of organic fertilizers levels on magnesium, manganese, zinc and copper content was also significant.

The application of organic fertilizers such as humic and fluvic acid along with chemical fertilizers can improve the morphological characteristics, provide the nutritional requirements of the plant and increase the phenolic compounds of olive leaves.

The application of organic fertilizers such as humic and fluvic acid along with chemical fertilizers can improve the morphological characteristics, provide the nutritional requirements of the plant and increase the phenolic compounds of olive leaves.