30 Years of N Fertilisation in a Forest Ecosystem - The Fate of Added N and Effects on N Fluxes

We investigated the fate of added N and its effect on N fluxes in a long-term nitrogen fertilisation experiment. Ammonium nitrate was added annually (30 years) at mean rates of 0 (N0), 35 (N1), 73 (N2) and 108 (N3) kg N ha super(-1) yr super(-1) to a spruce forest in Sweden, which initially showed s...

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Bibliographic Details
Published in:Water, air, and soil pollution air, and soil pollution, 2001-08, Vol.130 (1-4), p.637-642
Main Authors: Andersson, Pål, Berggren, Dan, Johnsson, Lars
Format: Article
Language:English
Subjects:
Amino acids
Ammonium
Ammonium nitrate
Coniferous forests
Environmental monitoring
Fertilization
Forest ecosystems
Leaching
Litter fall
Mineralization
Nitrogen
Soil microorganisms
Soil solution
Terrestrial ecosystems
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Summary:We investigated the fate of added N and its effect on N fluxes in a long-term nitrogen fertilisation experiment. Ammonium nitrate was added annually (30 years) at mean rates of 0 (N0), 35 (N1), 73 (N2) and 108 (N3) kg N ha super(-1) yr super(-1) to a spruce forest in Sweden, which initially showed signs of N deficiency. Net N mineralisation and N leaching were measured in situ together with soil N pools. We used the PnET-CN model to model the maximum sustainable net N mineralisation rate. The short-term fate of added N was studied by addition of super(15)NH sub(4)Cl. In N1 and N2 most of the added N (80-120%) was retained in the system, compared to 45% in N3. A major fraction was retained in the organic horizons (58-79%). The internal N fluxes had increased considerably as a result of the N additions. Net N mineralisation in N1 had increased by a factor 10 and litterfall N flux by a factor 4. The PnET-CN model could not mimic the fast changes in tree growth and N mineralisation, but the maximum N mineralisation rate seems realistic. The ratio of actual to maximum mineralisation rate indicates that the N1 treatment now is close to N saturation, and nitrate was occasionally found in soil solution from the B-horizon in N1. The N retained was probably to a great extent immobilised directly by mycorrhizal fungi, as indicated by the high amounts of super(15)N found in the L and F layers and by the great fraction of super(15)N found in amino sugars compared to amino acids.
ISSN:0049-6979
1573-2932
DOI:10.1023/A:1013896410589