Comparing the Effects of Urea and Ammonium Nitrate Fertilizers on the Growth and Foliar Nutrition of Lodgepole Pine: 6-year Results

The 6-year effects of urea (46--) and ammonium nitrate (AN; 34--) fertilizers, applied alone and in combination with other nutrients, on tree growth and foliar nutrition were evaluated in a -year-old, thinned lodgepole pine (Pinus contorta Dougl. var. latifolia Engelm.) stand in central British Columbia. Results indicate that lodgepole pine has no clear preference for a particular nitrogen (N) source, when applied alone or combined with other potential growth-limiting nutrients. Results also indicate that N-deficient lodgepole pine may not respond favourably to N fertilization unless other nutrients are combined with N in the fertilizer prescription. When applied alone, fall-applied AN and urea were relatively ineffective in stimulating tree growth at this site, apparently due to induced deficiencies of other nutrients (especially sulfur). Foliar nutrient status and growth were significantly improved by including a Complete fertilizer with both N sources. Results from this study do not suggest any reason for changing the current practice of using urea as the primary N source in large-scale fall fertilizer operations in the interior of British Columbia. However, further studies may be warranted to examine the effect of different N fertilizers on the growth of other interior species.