Fertilisation azotée en forêt de pin gris (Pinusbanksiana). III. Croissance du pin gris
Six nitrogen fertilizers (urea, sulfur-coated urea, urea-formaldehyde, ammonium sulfate, ammonium nitrate, and calcium nitrate) were individually applied, either in fall or in spring, at a rate of 224 kg N/ha and compared for their effects on growth distribution along the stem, height increase, basal area increase, and volume increase of an 18-year-old jack pine stand during 5 years after treatment. The response to nitrogen treatments was maximum the 2nd and 3rd years after fertilization and became nil in the fifth season. The distribution of growth along the stem varied with the height considered, the maximum being observed in the first 3 m aboveground. Treatments that responded best in terms of increase in basal area (2 m2/ha or 34% higher than control) and in volume (10 m3/ha or 21% higher than control) were urea and ammonium sulfate applied in fall, and ammonium nitrate applied in spring. Regression analysis on principal components revealed that growth the year before treatment and nutrient concentrations in foliage (N, P, K, Mg, Ca, and Mn) explain at least 80% of the observed growth variations on a 5-year basis.