THE EFFECT OF NITROGEN FERTILIZATION ON HEIGHT GROWTH OF DOUGLAS FIR ON A POOR SITE

Results of ten different nitrogen fertilizer treatments on seven-year-old, planted, open-grown Douglas fir on a low-quality site are presented. Annual height growth and foliar observations were used to indicate response. Results show an increase in height growth from fertilizer applications, except one, when compared to the control. The response to the four-ounce ammonium sulfate treatment suggests this amount to be optimum in this trial. Generally the greatest response was in the larger trees. Four of the fertilizer treatments caused needle defoliation. Two treatments killed trees.