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after fertilization (seasons of application combined), ammonium nitrate caused a 26% increase
over control in N content of current foliage, whereas urea caused a 13% increase. This superiority
of ammonium nitrate over urea was attributed to the nitrate ion.
426. Nason, G.E., D.J. Pluth and W.B. McGill. 1988. Volatilization and foliar recapture of ammonia
following spring and fall application of nitrogen-15 urea to a Douglas-fir ecosystem. Soil-
Science-Society-of-America-Journal 52(3): 821-828.
Keywords: fertilization
tree physiology
soil properties
Abstract: Seasonal effects on the volatilization and vegetal recapture of NH3 following
application of pelleted 15N urea at 200 kg N ha-1 to a 40-yr-old Douglas-fir [Pseudotsuga
menziesii] ecosystem were investigated. Volatilization totalled 14 and 0.7% of applied N in
spring and autumn, respectively, and the difference appeared to be related to precipitation
patterns following fertilization. Volatilization was generally enhanced by small spring rainfalls
while depressed by larger autumn rains. The isotopic abundance of evolved NH3 fluctuated from
>90 to 1-year-old foliage > roots which
is consistent with anabolic incorporation and translocation. This mechanism may have a
significant role in plant nutrition when conditions favourable to NH3 volatilization follow urea
fertilization.
427. Nelson, E.E. 1989. Black bears prefer urea-fertilized trees. Western-Journal-of-Applied-Forestry
4(1): 13-15.
Keywords: fertilization
tree/stand health
Abstract: Feeding damage by the black bear (Ursus americanus) to urea-fertilized 25-yr-old
Douglas fir (Pseudotsuga menziesii) in the Mount Hood National Forest, Oregon, resulted in tree
mortality 4x as severe as among unfertilized trees. Damage was most apparent following
application of urea at 448 kg N/ha in 1972, and 224 kg N/ha in 1977. Only Douglas fir, the
dominant species in the stand, was attacked (western hemlock (Tsuga heterophylla), western red
cedar (Thuja plicata) and red alder (Alnus rubra) were scattered through the stand). Attacked trees
were somewhat larger than the stand average but the difference was not significant. Bears
appeared to be attracted to the more vigorous trees, which were on fertilized plots.
428. Nelson, E.E., M.G. McWilliams and W.G. Thies. 1994. Mortality and growth of urea-fertilized
Douglas-fir on a Phellinus weirii-infested site in Oregon. Western-Journal-of-Applied-Forestry
9(2): 52-56.
Keywords: planting operations
fertilization
tree/stand protection
growth
tree/stand health