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Long‐Term Effects of Nitrogen Fertilization on Nitrogen Availability in Coastal Douglas‐Fir Forest Floors
Author(s) -
Chappell H. N.,
Prescott C. E.,
Vesterdal L.
Publication year - 1999
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1999.6351448x
Subject(s) - human fertilization , cycling , plant litter , nitrogen cycle , litter , mineralization (soil science) , agronomy , nitrogen , zoology , forest floor , nitrification , environmental science , nutrient , ecology , biology , soil water , chemistry , forestry , soil science , geography , organic chemistry
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.