Mortality and Growth of Urea-Fertilized Douglas-Fir on a Phellinus weirii-Infested Site in Oregon
Twelve plots were established in 1972 in an 11-yr-old Douglas-fir (Pseudotsuga menziesii) plantation infected with Phellinus weirii, the cause of laminated root rot. All plots were thinned and either interplanted with red alder (Alnus rubra) or fertilized at 5-10 yr intervals with urea to determine the effect of nitrogen on tree growth and mortality caused by P. weirii, or left untreated. Interplanted alder, however, failed to survive. Mortality was assessed at intervals of 2 to 3 yr. Plots were inventoried (100% cruise) in 1978 and 1990. Growth over 12 yr appeared better on fertilized than nonfertilized plots, but the difference was not significant (alpha = 0.05 ). Mortality caused by the preferential feeding of bears on the inner bark of fertilized trees reduced the overall gain. Mortality caused by laminated root rot did not differ significantly (alpha = 0.05) among treatments. Three months after the initial application of urea at 448 kg N/ha, soil sampled to a depth of 30 cm was higher in ammonium and nitrate forms of nitrogen on fertilized than nonfertilized plots, but increases were not significant (alpha = 0.05). Numbers of bacteria were directly correlated with soil ammonium content (P = 0.1092). Numbers of aerobic actinomycetes were inversely correlated with soil nitrate content (P = 0.0398).West. J. Appl. For. 9(2): 00-00.
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Document Type: Journal Article
Affiliations: USDA Forest Service, Pacific Northwest Research Station, Forestry Sciences Laboratory, 3200 Jefferson Way, Corvallis, OR 97331
Publication date: 01 April 1994