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Résumé :
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Concentrations of N, P, K, Ca and Mg were determined in foliage from hybrid larch from 15 sites and 30 plots in total. Total height and girth at breast height were measured in order to estimate site index. Analysis of variance revealed a high variability both between sites, between plots within sites and within plots for vigour traits and site index (less than 4 to more than 15 m3 ha-¹ year-¹). In addition, foliar concentrations of major elements were highly variable between sites : 1.49-3.11% N, 1.1-4.5 g kg-¹ P, 5.2 - 9.5 g kg-¹ K, 1.9-9.8 g kg-¹ Ca and 0.4-2.5 g kg-¹ Mg. Ratios of N/P, N/Mg and K/Ca varied from 4.8 to 21.2, 0.4 to 47.2 and 0.6 to 4.3, respectively. With respect to the level of site index, the following values could be considered as optimal concentrations for hybrid larch: 1.95-2.73% N, 1.4-2.4 g kg-¹ P, 5.2-8.6 g kg-¹ K, 3.3-6.2 g kg-¹ Ca and 1.1-2.0 g kg-¹ Mg, with ratios of 9.9-14.4 for N/P, 13.7-17.7 for N/Mg and 1.0-1.6 for K/Ca. Such conditions were observed in plots where soil acidity was classified as moderately acidic to neutral. Except for nitrogen, hybrid larch did not appear in this study to have higher nutrient requirements than other major conifers such as Norway spruce or Douglas fir. However, it is one of the most reactive species to fertilisers.
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