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

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 (an alysed by GLC) and yield of fennel essential oil constituents grown with tw o soil (S) levels (60 kg N + 27 kg P and 90 kg N + 40 kg P ha(-1)). Camphen e and d-fenchone, both being bicyclic monoterpenes, and d-alpha-pinene, ano ther bicyclic monoterpene showed a similar trend (R = 0.87) and their conte nts were maximum with FN20P2 at both soil levels. Methylchavicol and anetho le (Phenylpropanoids) exhibited parallel trends (R = 0.56), with the contro l giving higher values at both soil levels. Interestingly, there was a nega tive correlation between some of the constituents, e.g, anethole versus d-f enchone (R = -0.99), anethole versus camphene (R = -0.87), and methylchavic ol and d-alpha-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 e nhanced the contents (%) of the phenylpropanoids (anethole and methylchavic ol) while their foliar application increased the monoterpenes (d-fenchone, camphene and d-alpha-pinene). It is concluded that appropriate combinations of basal and foliar nutrients could be exploited to obtain higher yields o f the desired constituents of fennel oil.