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Determination and Isotope-Ratio Analysis of Different Forms of Nitrogen in Soils: 2. A Simplified Procedure for Isotope-Ratio Analysis of Soil Nitrogen¹

ABSTRACT

A procedure for isotope-ratio analysis of soil nitrogen is described which eliminates the ammonium distillation stage of the customary procedure. The nitrogen in the soil sample is converted to ammonium by Kjeldahl digestion without use of a catalyst, digestion being accomplished by heating the sample with sulfuric acid containing a high concentration of potassium sulfate (ca. 0.7g/ml of H₂SO₄). An aliquot of the digest is partially neutralized and treated in vacuo with alkaline hypobromiteiodide solution, and the N₂ liberated by this treatment is analyzed by the mass spectrometer. This simplified procedure eliminates problems encountered in distillation and concentration of ammonium samples for N¹⁵ analysis and gives the same results as the customary procedure.

¹ Journal Paper no. J-5249 of the Iowa Agr. and Home Econ. Exp. Sta., Ames. Project no. 1070. This work was supported in part by TVA.

² Formerly Assistant Professor and Professor, respectively, Department of Agronomy, Iowa State University, Ames. The senior author is now Assistant Professor of Soils, Washington State University, Pullman.

Received for publication November 16, 1965. Accepted for publication March 25, 1966.