Fertilisation azotée en forêt de pin gris (Pinusbanksiana) II. Variations de la masse foliaire et des éléments nutritifs du feuillage de pin gris et de quelques espèces du sous-bois
Fall or spring applications of six different nitrogen fertilizers (urea, sulfur-coated urea, urea-formaldehyde, ammonium nitrate, ammonium sulfate, and calcium nitrate) at a rate of 224 kg N/ha in an 18-year-old jack pine stand induced a very rapid increase of nitrogen concentration in current year and 1-year-old needles, as well as in weight of current year needles. In the latter, nitrogen content (concentration × weight) increased more than 100% the 1st year following fertilization in the ammonium sulfate and the ammonium nitrate treatments applied in spring. Response did not last more than 2 years. Foliar analysis of other elements (P, K, Ca, Mg, and Mn) revealed a reduction of P concentration in the needles sampled the first fall after treatment together with a reduction of Ca and Mn in the current foliage of the second and third seasons after treatment. Changes in nitrogen concentration in Kalmiaangustifolia L. and particularly in Solidagopuberula Nutt. were in good correlation with those observed in jack pine needles.