Khan, M. M. A., Azam, Z. M. and Samiullah. 1999. Changes in the essential oil constituents of fennel (Foeniculum vulgare) as influenced by soil and foliar levels of N and P. Can. J. Plant Sci. 79: 587-591. 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 + 40 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. , montrant que la synthèse d'un des constituants se faisait aux dépens de l'autre. La fumure N et P du sol augmentait la proportion des phénylpropanoïdes, tandis que la fertilisation foliaire accroissait celle des monoterpènes. Une bonne combinaison des fertilisants apportés au sol ou par voie foliaire, pourrait être utilisée pour obtenir un rendement plus élevé des composants recherchés de l'huile du fenouil.