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Determination and Isotope-Ratio Analysis of Different Forms of Nitrogen in Soils: 3. Exchangeable Ammonium, Nitrate, and Nitrite by Extraction-Distillation Methods¹

ABSTRACT

Methods of determining exchangeable ammonium, nitrate, and nitrite in soils are described. They involve extraction of the soil sample with 2M KCl (10 ml/g of soil) and analysis of the extract by steam-distillation methods in which magnesium oxide is used for distillation of ammonium, ball-milled Devarda alloy for reduction of nitrate and nitrite to ammonium, and sulfamic acid for destruction of nitrite. The distillation methods are rapid, accurate, and precise, have high specificity, and are applicable to turbid, colored, and unfiltered soil extracts. They give quantitative recovery of ammonium, nitrate, and nitrite added to soil extracts and permit nitrogen isotope-ratio analysis of these forms of nitrogen in N¹⁵-tracer studies of nitrogen transformations in soils.

¹ Journal Paper no. J-5334 of the Iowa Agr. and Home Econ. Exp. Sta., Ames. Projects 1070 and 1450. This work was supported in part by the Tennessee Valley Authority. Presented in part before Div. S-3, Soil Science Society of America, at Denver, Colo., Nov. 18, 1963.

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

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