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Soil Science Society of America Journal Abstract -

Immobilization of Nitrogen-15-Labelled Urea in a Jack Pine Forest Floor1


This article in SSSAJ

  1. Vol. 49 No. 2, p. 448-452
    Received: Feb 21, 1982
    Accepted: Oct 10, 1984

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  1. N. W. Foster,
  2. E. G. Beauchamp and
  3. C. T. Corke2



Urea labelled with 15N was applied at 200 kg N ha−1 in the spring to a 45-yr-old natural jack pine (Pinus banksiana Lamb.) forest near Chapleau, ON. Fertilizer recovery in the L and F horizons was determined 32, 64 and 96 d after fertilization. Three months after fertilization, 25% of the added N had been immobilized in the forest floor and was recovered as organic N. The possibility that chemical reactions contribute to fertilizer N immobilization was investigated by applying urea to sterilized, mixed L and F horizon materials in an 8-d laboratory incubation study. The amount of N fixed chemically in urea-treated forest floor materials exceeded the amount of N immobilized in microbial tissue. The nature of the chemical reaction was investigated in a second incubation study. Urea did not react with L + F horizon materials either at the natural soil pH (4.5) or at the higher pH (8.0) resulting from the addition of KOH. Since urea was applied at a rate sufficient to raise soil pH to the alkaline range, immobilization may be explained by reaction between NH3 and soil organic matter.

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