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NON-EXCHANGEABLE BINDING OF AMMONIUM AND AMINO NITROGEN BY NORWAY SPRUCE RAW HUMUS

HANS NÕMMIK
Plant and Soil
Vol. 33, No. 3 (December 1970), pp. 581-595
Published by: Springer
Stable URL: http://www.jstor.org/stable/42932803
Page Count: 15
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NON-EXCHANGEABLE BINDING OF AMMONIUM AND AMINO NITROGEN BY NORWAY SPRUCE RAW HUMUS
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Abstract

The capacity of an originally acid Norway spruce raw humus to fix isotopically labelled ammonium and amino nitrogen in a form resistant to cold 1 N HCl treatment was studied. The amount fixed was determined after a reaction period of 24 hours (the humus pretreated with propylene oxide), using the amount of labelled N in the HCl-leached humus residue as a basis for calculating the amount of added N fixed. The nitrogen sources used were ammonium chloride, glycine and cyanamide. It was found that the fixation of added ammonium and glycine N was exceedingly low in the H⁺-saturated raw humus (pH 3.3-3.4), but the fixation rate was rapidly increased by increasing the pH during the aerobic incubation. Maximum fixation was obtained at a final pH of 10-11. Within the acid range the fixation was constantly higher for added glycine-N than ammonium-N. On the alkaline side of the neutral point the amount of fixation tended to be similar for ammonium and glycine. In treatments with N¹⁵-labelled ammonium, it was shown that small but fully detectable amount of added N were present in the soluble organic N fraction of the HCl extract, the quantities increasing with increasing soil pH during the incubation. The fixation was increased by increasing temperature and decreased by oxidative pretreatment of the humus before the addition of N. In the nitrogen gas atmosphere the fixation figures were 40 to 50 per cent lower than for corresponding treatments in air atmosphere. When various N compounds were added in equimolar concentrations the highest fixation was recorded for cyanamide. In studying the stability of fixed N to acid hydrolysis, it was found that 54 per cent of the fixed N resisted eight hours' refluxing with 6 N HCl, the corresponding figure for the native raw humus N being 19 per cent. About one third of the fixed N was liberated as ammonia during the acid hydrolysis.

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