Blessed Thistle Growth, Essential Oil Content, Yield and Composition as Influenced by Plant Density and Nitrogen Fertilizer

Abstract

Blessed thistle (Cnicus benedictus L.) is an abundant resource with huge phytochemical and agronomic potentials. Their variation in response to agronomic techniques needs to be explored. Field studies were laid out to assess plant density and nitrogen fertilizer (N) effects on blessed thistle plant height, branches number (m^-2), vegetative variables and RGR (relative growth rate), CGR (crop growth rate), LAR (leaf area ratio), NAR (net assimilation rate), as growth variables along with blessed thistle essential oil content, yield and compositions in two growing seasons. A three replicated factorial combination of plant densities (5, 10, 15, 20 and 25 plants m^-2) and N levels (0, 50, 100 and 150 kg ha^-1) in a randomized complete-block design were conducted. Addition of 100 kg N ha^-1with 15-20 plants m^-2caused a significant increase in vegetative and growth variables. Although the essential oil content declined by 28 and 39 % as N rate level rose from 0 to 150 kg ha^-1, essential oil yield peaked at 40-80 kg N ha^-1 in both years. The GC and GC/MS analysis showed that eicosane was the dominant component of the essential oil (31-65 %), followed by isopropyl hexadecanoate (5.7-9.2 %), octadecane (3.5-10.5 %) and cryptomerione (3.1-7.1 %) which presented variations across the treatments. Application of N resulted in a decrease in the eicosane and an increase in the proportion of isopropyl hexadecanoate, octadecane and cryptomerione. It can be concluded that optimizing agronomic management techniques could be an effective approach to improve growth, essential oil content and composition of the plant.

Key words:

• Agronomic techniques
• growth analysis
• essential oil composition
• eicosane