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This article in SSSAJ

  1. Vol. 30 No. 2, p. 210-213
    Received: Aug 6, 1965
    Accepted: Oct 29, 1965

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Mineralization and Immobilization of Nitrogen in Bacterial Cells and in Certain Soil Organic Fractions1

  1. J. P-H. Chu and
  2. R. Knowles2



Nitrogen15-enriched Pseudomonas cells and (NH4)2SO4 were added separately to a Chicot sandy loam and to a black spruce raw humus (F horizon). At intervals from zero to 100 days the soil N was fractionated (Cheng and Kurtz, 1963) into: exchangeable NH4+- + NO3--N, fixed NH4+-N, N in acid hydrolyzate (i.e. NH4+ from hydrolysis, amino sugar-N, amino acid-N, acid-soluble alkali-insoluble humin-N), and acid insoluble humin-N.

At zero time 92.5 and 93.0% of the added NH4+-N appeared in the exchangeable fraction of the two soils, respectively; 55.3 and 83.7% of the added cell-N appeared in the amino acid fraction of the two soils, respectively. During incubation in both soils about 40% of the added NH4+-N remained in the exchangeable fraction and 50 to 60% was immobilized in the amino acid fraction. In the raw humus about 13% of the added NH4+-N appeared in the insoluble humin fraction. In both soils 20–30% of the added cell-N was rapidly mineralized but at least 50% remained in the amino acid fraction. There was evidence of a “priming effect” or “N interchange” resulting in increased mineralization of native soil organic N. This effect was particularly pronounced in the raw humus.

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