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Research Branch > Stand Management > Fertilization > EP 886.14
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.
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