Sessile oak seedling fertilization and leaf mineral composition in western France

Three experiments were conducted in the Foret de Blois, in western France, on leached chemically poor soils with limited water drainage (stagnic luvisols in the FAO classification), in young (2-10-year-old) sessile oak seedlings from natural regeneration. The main limiting factors for growth were phosphorus and nitrogen. In the better soils (0.09 g.kg(-1) P2O5 in the A(1) horizon extracted by H2SO4 extraction followed by OHNa extraction, according to the Duchaufour method), PKCa fertilization was not efficient and addition of N was necessary to improve height and diameter growth. In the poorest soils (0.03 g.kg(-1)-P2O5 in the A(1) horizon), PKCa fertilization without N enabled a 40% gain in height and a complete NPKCa fertilization enabled a 100% gain during at least 5 years. Optimum composition for leaves sampled in August and ratios between elements were estimated as: N: 23 mg.g(-1); P: 1.5 mg.g(-1); K: 8.6 mg.g(-1); Ca: 9 mg.g(-1); N/P: 15, N/K: 2.7; K/P: 5.6.