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Soil Science Society of America Journal Abstract - DIVISION S-7-FOREST & RANGE SOILS

Long-Term Effects of Nitrogen Fertilization on Nitrogen Availability in Coastal Douglas-Fir Forest Floors


This article in SSSAJ

  1. Vol. 63 No. 5, p. 1448-1454
    Received: Sept 3, 1998

    * Corresponding author(s): cpres@interchange.ubc.ca
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  1. H. N. Chappella,
  2. C. E. Prescott *b and
  3. L. Vesterdalc
  1. a College of Forest Resources, Univ. of Washington, Seattle, WA 98195 USA
    b Faculty of Forestry, Univ. of British Columbia, 2424 Main Mall, Vancouver, BC V6T 1Z4, Canada
    c Dep. of Forest Ecology, Danish Forest and Landscape Research Institute, Hørsholm Kongevej 11, DK-2970 Hørsholm, Denmark


It has been suggested that a long-term increase in N availability could be achieved by repeated N fertilization of forests, and that the increase in N availability would be greatest at initially N-rich sites. The aim of this study was to determine if N availability was elevated 8 to 12 yr after repeated N fertilization, and if the effects of N fertilization were related to the soil N capital. Rates of N cycling in control and fertilized plots of Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] were compared by measuring net N mineralization rates in forest floors and by estimating rates of N turnover from the litterfall/forest floor ratio. Litterfall N contents, litter N concentrations, and rates of N turnover increased along the gradient in soil N capital in both control and fertilized stands. Fertilization did not affect litterfall N content, but C/N ratios of litter and forest floors were significantly lower in fertilized stands along the gradient. Turnover rates of N in the forest floors were not higher in fertilized plots than in control plots, nor were rates of net N mineralization affected by fertilization. Net nitrification rates were higher in some of the plots that received 1120 kg N ha−1 than in control plots. We conclude that N fertilization did not result in a sustained increase in N cycling and N availability analogous to a higher site N capital, and that the effect of N fertilization was not related to the initial soil N capital of these sites.

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