Immobilization of Nitrogen-15-Labelled Urea in a Jack Pine Forest Floor1
- N. W. Foster,
- E. G. Beauchamp and
- 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.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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