Changes in the essential oil constituents of fennel (Foeniculum vulgare) as influenced by soil and foliar levels of N and P

Abstract

In a split-plotfield trial, the effect of foliar (F) application of 0 or 20 kg N, 2 kg P or 20 kg N + 2 kg P ha−1.was studied on the composition (analysed by GLC) and yield of fennel essential oil constituents grown with two soil (S) levels (60 kg N + 27 kg P and 90 kg N + 0 kg P ha−1). Camphene and dfenchone, both being bicyclic monoterpenes, and d-α-pinene, another bicyclic monoterpene showed a similar trend (R = 0.87) and their contents were maximum with FN20P2 at both soil levels. Methylchavicol and anethole (Phenylpropanoids) exhibited parallel trends (R = 0.56), with the control giving higher values at both soil levels. Interestingly, there was a negative correlation between some of the constituents, e.g. anethole versus d-fenchone (R = −0.99), anethole versus camphene (R = −0.87), and methylchavicol and d-α-pinene (R = −0.71), suggesting that the synthesis of the one constituent was at the expense of the other. Soil application of N and P enhanced the contents (%) of the phenylpropanoids (anethole and methylchavicol) while their foliar application increased the monoterpenes (d-fenchone, camphene and d-α-pinene). It is concluded that appropriate combinations of basal and foliar nutrients could be exploited to obtain higher yields of the desired constituents of fennel oil. Key words: Anethole, d-fenchone, d-α-pinene, camphene, methylchavicol, correlation