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Comparison and Evaluation of Methods of Determining Fixed Ammonium in Soils¹

ABSTRACT

A comparison of methods proposed for determination of fixed ammonium in soils showed that they gave widely divergent results, the highest results being obtained by the method of Rodrigues and the lowest by the method of Mogilevkina. Studies to evaluate these methods revealed defects in all methods investigated except the KOBr-HF method of Silva and Bremner, the main defects being that pretreatments used to eliminate interference by organic nitrogen compounds are inefficient or lead to gain or loss of fixed ammonium and that procedures used to release and estimate fixed ammonium are not quantitative or lead to formation of ammonium from organic nitrogen compounds. Possible defects of the KOBr-HF method are discussed.

¹ Journal Paper J-5546 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.

² Professor, Research Associate, and Graduate Assistant, respectively, Dep. of Agronomy, Iowa State Univ., Ames. J. A. Silva is now Assistant Professor of Soils, University of Hawaii, Honolulu.

Received for publication November 4, 1966. Accepted for publication February 4, 1967.