The response of a 40-year-old even-aged jack pine (Pinusbanksiana Lamb.) stand to nitrogen fertilization was studied in four experiments.Smothering of the ericaceous ground vegetation layer with straw led to increased tree growth rates and improved N uptake. The application of calcium nitrate, ammonium nitrate, and urea at 112 and 448 kg N/ha was followed by analysis of the composition of extractable humus N, together with foliar and increment analyses. After a 3-year response period, there was evidence for the superiority of the ammonium nitrate form of N fertilizer over urea. The applications of urea appear to have been associated with possible N volatilization losses, and also inadequate urease activity in the thin dry humus layer which led to delayed N uptake by the trees. Calcium nitrate, although not an efficient fertilizer, was associated with appreciable growth responses, even though increased foliar and extractable humus N concentrations were not maintained.An optimum nutrition experiment utilizing repeated fertilization indicated that sustained foliar nutrient regimes can be maintained.The study indicated that growth increases were associated with increased unit needle weights as well as increased foliar N concentrations. A graphical technique which analyzes treatment responses, unit needle weight, and nutrient concentration, was used to screen response data, without waiting the customary 5-year period for stem increment response.