A COMPARISON OF METHODS OF DETERMINING NITROGEN FRACTIONS IN SOILS

Abstract

The ammonia, hexosamine, and amino acid nitrogen fractions of soil hydrolyzates were determined with the Technicon autoanalyzer and the results compared with those from other more rapid methods of analysis. Ammonia determination by steam distillation agreed well with that by the autoanalyzer. Amino acid nitrogen, as determined by direct color development with ninhydrin and as ammonia after ninhydrin oxidation, agreed well with total amino acid nitrogen. Steam distillation was not a very satisfactory method of determining hexosamine nitrogen, probably because it was determined by difference between total distillable and distillable ammonia and the hexosamine nitrogen was small relative to the total nitrogen distilled.The soils tested contained approximately 20% acid-insoluble nitrogen. The acid hydrolyzate contained approximately 36% of total soil nitrogen as amino acid nitrogen, about 22% as ammonia nitrogen, and about 4% as hexosamine nitrogen. Approximately 20% of the soil nitrogen appeared in the hydrolyzate in a soluble form which was not identified by the methods used. A method is proposed which appears suitable for routine analysis of the nitrogen fractions of soils.