Effects of iron and zinc chelates foliar application on growth characteristics, essential oil content, and asafetida of Ferula assa-foetida L. under supplementary irrigation conditions

To study the effects of different levels of iron and zinc chelates application and supplementary irrigation on the quantity and quality of Ferula assa-foetida L. asafetida, a factorial experiment was conducted in a randomized complete block design with three replications in Neyriz City (Fars province) in 2018. The experimental treatments included the supplementary irrigation (no irrigation (control), once, and twice irrigation) and zinc and iron chelates foliar application (no foliar application (control), Zn (two per thousand) foliar application, Fe (two per thousand) foliar application, and combined Fe (1.5 per thousand) and Zn (1.5 per thousand) foliar application). The studied traits included the number of leaves, leaf length, crown diameter, aerial parts dry weight, plant survival percentage, concentration of elements Fe, Mn, Cu, and Zn in the aerial parts, asafetida weight, and essential oil content. The results showed that the supplementary irrigation increased the number of leaves, aerial parts dry weight, and survival percentage of the plant. Twice supplementary irrigation resulted in the highest aerial parts Fe content. Also, the iron and zinc chelates foliar application increased the leaf length and survival percentage of the plant compared to the control. The highest aerial parts Fe content was obtained by iron chelate foliar application. Under both supplementary and control irrigation conditions, the zinc and iron chelates foliar application significantly increased the plant volume by 1.5 times, asafetida weight by 2 to 2.8 times, and essential oil content by 0.6 to 0.9%. In addition, under no supplementary irrigation conditions, the highest aerial parts Mn content of the plant was obtained by zinc chelate foliar application as well as combined iron and zinc chelates foliar application, but under once and twice supplementary irrigation conditions, the foliar application had no significant effect on this parameter. Under both supplementary and control irrigation conditions, the highest aerial parts Cu content of the plant was observed in no foliar application treatment. The Zn foliar application caused the highest aerial parts Zn content of the plant. Therefore, it seems that the supplementary irrigation with the foliar application of iron and zinc chelates could increase the asafetida yield and essential oil content in F. assa-foetida by improving the growth characteristics.