Response of young lodgepole pine to spring and fall applications of urea and ammonium nitrate fertilizer (E.P. 886.04)


In the Pacific Northwest (PNW) region of the United States and Canada, urea (46-0-0, N-P-K) is the only nitrogenous fertilizer operationally applied to forests. This reflects urea's relatively low unit price and high nitrogen (N) analysis. Large-scale forest fertilization research studies in the PNW have all used urea as the primary N source. Comparisons of tree response to applications of urea relative to other N sources in the PNW are largely restricted to a number of small studies in coastal Douglas-fir forests. Several of these studies have reported greater growth responses with ammonium nitrate (34-0-0, N-P-K) than with urea. Other coastal fertilization studies, however, have reported no differences between these two N sources.

In Sweden, fertilization studies in Scots pine and Norway spruce forests show larger growth response to ammonium nitrate (AN) than to urea. Ammonium nitrate is the preferred N source for fertilizer operations in Sweden.


The objectives of this study are to: i) compare differences in growth response of lodgepole pine in the interior of British Columbia to spring and fall applications of urea and ammonium nitrate fertilizer, and ii) examine the nature of a N source x season of application interaction.


A total of three, "single-tree" fertilizer trials were established in thinned lodgepole pine stands in 1984. Each of the trials was designed as a 2 x 2 factorial experiment using two N sources (AN and urea) and two seasons of application (spring and fall). An additional unfertilized treatment served as a control. Both N sources were applied at a rate of 200 kg N/ha. Each of the five treatments was randomly assigned to 15, "single-tree" plots. Fertilizer was applied by hand to a 5m radius area surrounding each selected "plot" tree.

All installations were measured at the time of establishment and again after 3 and 6 years. Measurements included diameter at breast height, total height, height to live crown, tree form and damage. Foliar nutrient data were also obtained from all treatment plots prior to fertilization and after 1 and 3 years.

The study is now inactive.


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The Ministry of Forests, Lands, Natural Resource Operations and Rural Development Publications Search

  • Brockley, R.P. 2000. Using foliar variables to predict the response of lodgepole pine to nitrogen and sulphur fertilization. Can. J. For. Res. 30:1389–1399.
  • Brockley, R.P. 1995. Effects of nitrogen source and season of application on the nutrition and growth of lodgepole pine. Can. J. For. Res. 25:516–526.
  • Brockley, R.P. 1989. The response of young lodgepole pine to spring and fall applications of urea and ammonium nitrate fertilizer. B.C. Min. For., Victoria, B.C. FRDA Res. Memo 120.