Ureolysis, Immobilization, and Nitrification in Black Spruce (Picea mariana Mill.) Humus1, 2
- M. R. Roberge3 and
- R. Knowles4
The transformations of urea in black spruce humus from an untreated plot and from a plot fertilized with 400 lb urea-N/acre 2 years before sampling were studied using incubation tests. Urea-N (3,500 ppm) added in the laboratory disappeared within 2 days. During the first 3 days, exchangeable ammonium-N equivalent to about 82% of the added urea-N appeared and the pH increased by 1.5 units, but no nitrates were formed. Thereafter, and up to 42 days, there was a very small immobilization of the ammonium-N and a decrease in pH of approximately 0.5 unit. Nitrification occurred only after 28 days, and then only in the field-treated humus when urea was again added in the laboratory. The addition of (NH4)2CO3-N (3,500 ppm) had very similar effects except that a slightly greater rise in pH was accompained by somewhat more immobilization of the ammonium-N than occurred following the addition of urea.
It is concluded that ureolysis was very rapid; that, in spite of the high C/N ratio, immobilization was small; and that, in most treatments, nitrification was negligible, and therefore leaching of nitrates following the fertilization of acid forest soils with 400 lb urea-N/acre is not likely to be a problem.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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