Foliar application of Ca(NO3)2 and KNO3 affects growth, essential oil content, and oil composition of French tarragon

French tarragon (Artemisia dracunculus L.) is a perennial herb in the family Asteraceae that is widely cultivated throughout the word. In order to study the effect of foliar application of Ca(NO3)2 and KNO3 on vegetative traits, essential oil yield, content and composition, a field experiment was conducted. Treatments including four levels of Ca(NO3)2 and KNO3 fertilizers (0, 1.5, 3, and 6 g/l) were set up in a factorial experiment based on Randomized Completely Block Design with three replications. The results showed that Ca(NO3)2 application significantly affected all tarragon vegetative traits, but had no significant effect on essential oil content. Furthermore, essential oil yield increased with Ca(NO3)2 treatments by an average of 64.4% compared to the control. Ca(NO3)2 fertilization increased leaf K and Ca contents. The gradual increase of Ca(NO3)2 rates decreased estragole by 18.6%. On the other hand, KNO3 fertilization significantly increased all of plant growth characters, leaf K and Ca contents. Foliar KNO3 application significantly increased essential oil content and the yield by an average of 42.5% and 119.6%, respectively. The lowest content percentage of estragole (76.83%) is obtained from 1.5 g/l KNO3 decreased by 0.6% an average when compared to the control. The interactive application of Ca(NO3)2 and KNO3 significantly affected the number of branch/plant, leaf K content and all of the essential oil constituents. Interactive treatment of Ca(NO3)2 and KNO3 decreased estragole content by an average of 12.9%. In general, it can be concluded that foliar application of Ca(NO3)2 and KNO3 can considerably improve the productivity traits, essential oil content, yield and composition of tarragon plant.