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Effects of Nitrogen Source on the
Growth of Lodgepole Pine (EP 886.14)


Introduction

Forest research studies and large-scale fertilizer operations in British Columbia and in the western United States have all used urea as the primary N source. This reflects urea´s relatively low unit price and high N analysis (46% N). This combination of factors results in lower transport and spreading costs per unit of added N compared with other available N sources. However, Scandinavian fertilization studies have reported consistently larger growth response to ammonium nitrate (AN) than to urea. In BC, results from fertilizer screening trials indicated no clear effect of N source on the growth of lodgepole pine. Despite the superiority of AN over urea in improving foliar N status, the stem growth response of fertilized trees was not affected by N source. The results indicated that a foliar N:S imbalance, and induced S deficiency, may have been created by the higher foliar N levels in AN-fertilized trees. It was determined that further studies were needed to determine whether AN is better than urea at stimulating tree growth when added in combination with other essential nutrients.

In 1999, the BC Ministry of Forests, Research Branch established an area-based N source experiment in a 24-year-old, harvest-origin stand within the Stuart Dry Warm variant of the SBS biogeoclimatic subzone (SBSdw3) west of Prince George.

Objectives

To determine the effects of two N sources (urea and ammonium nitrate), each applied with and without other nutrients, on the magnitude and duration of growth response in young lodgepole pine.

Treatments

The treatments include two N sources (urea and ammonium nitrate), each applied alone and in combination with a "Complete Mix" fertilizer (100P, 100K, 75S, 38Mg, 3B), and an unfertilized control. Nitrogen is applied at a rate of 300 kg/ha in all fertilizer treatments. The five treatments are each replicated three times, for a total of 15 treatment plots. Each circular, 0.07-ha treatment plot consists of an inner assessment plot surrounded by a treated buffer. Growth data are collected from 50 trees within each assessment plot every 3 years. Measurements include diameter at breast height, total height, height to live crown, tree form and damage. Foliar nutrient data were obtained from all treatment plots prior to fertilization, and will also be collected after 1, 3, and 6 years.

Publications

Brockley, R.P. 2006. Comparing the effects of urea and ammonium nitrate fertilizers on the growth and foliar nutrition of lodgepole pine: 6-year results. B.C. Ministry of Forests and Range, Victoria. Extension Note 78.

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Last Modified: 2007 APR 20.  Ministry contact: Frank van Thienen
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