Different forms of nitrogen in particle size fractions separated from two soils

Summary

The possible use of particle size separation of soils in water was tested for preparing fractions rich in ‘unknown’-N, which constitutes between 41 and 46% of the total N. Ten particle size fractions ranging from <0.2 to>1,000.0 μm were separated from the A horizon of the Bainsville soil, an Orthic Humic Gleysol, and from the Bh horizon of the Armadale soil, a poorly drained Podzol. The distribution of N (hydrolyzable-, amino acid-, protein-, amino sugar-, ammonia-, ‘unknown’-and unidentified-N) in the initial soils and in each size fraction was determined. While particle size separation did not yield fractions which contained essentially only ‘unknown’-N and few known N-components, it was possible to isolate fractions which were either rich in amino acid-or protein-N or in NH₃-N. In general, the finer size fractions tended to be enriched in amino acid-N while NH₃-N was more prominent in the coarser fractions. The amino sugar-N content of all size fractions was low.