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Determination and Isotope-Ratio Analysis of Different Forms of Nitrogen in Soils: 4. Exchangeable Ammonium, Nitrate, and Nitrite by Direct-Distillation Methods¹

ABSTRACT

Methods of determining exchangeable ammonium, nitrate, and nitrite in soils which do not require extraction of the soil sample are described. The soil sample is treated with 2M KCl (5 ml/g of soil) and analyzed directly by steam-distillation methods involving use of magnesium oxide for liberation of ammonium, ball-milled Devarda alloy for reduction of nitrate and nitrite to ammonium, and sulfamic acid for destruction of nitrite. The methods are rapid, specific, and precise, and they permit nitrogen isotope-ratio analysis of exchangeable ammonium, nitrate, and nitrite in N¹⁵-tracer studies of nitrogen transformations in soils. Results of soil analyses by these direct-distillation methods are practically identical to those obtained by extraction-distillation methods.

¹ Journal Paper no. J-5337 of the Iowa Agr. and Home Econ. Exp. Sta., Ames. Projects 1450 and 1070. Presented in part before Div. S-3, Soil Science Society of America at Denver, Colo., Nov. 18, 1963. This work was supported in part by the Tennessee Valley Authority.

² Research Associate and Professor, respectively, Department of Agronomy, Iowa State Univ., Ames.

Received for publication February 28, 1966. Accepted for publication April 18, 1966.