Chemical Distribution of Added Nitrogen in Soils
1963
Cheng, H. H. | Kurtz, L. T.
The distribution of added nitrogen (N) among the various components of soil N was determined, using isotopic tracing techniques. Three lysimeter soils, previously fertilized with N¹⁵-enriched N, were studied. Methods of fractionating soil N were modified to permit estimation of the isotopic ratio as well as the N content of the different fractions. Soil N was fractionated into: exchangeable NH₄⁺ plus NO₃⁻, fixed NH₄⁺, N in acid hydrolyzate, and acid-insoluble humin N. The N in acid hydrolyzate was further separated into the alkali-labile N and the alkali-stable N. The alkali-labile N consisted of hydrolyzed NH₄⁺ and amino sugar N. The alkali-stable N was divided into soluble N, which included the amino acid N, and acid-soluble but alkali-insoluble humin N. Validity of the classification was discussed. Usefulness of N¹⁵ data was also evaluated. Estimation of the distribution of added N showed that over 90% of added N in soils was found in the hydrolytic products of soil organic matter, mainly as amino acid N, amino sugar N, and other soluble N.
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