Factors affecting immobilization and release of nitrogen in soil and chemical characteristics of the nitrogen newly immobilized III. Transformation of the nitrogen immobilized in soil and its chemical characteristics

The immobilization and release process of nitrogen and the chemical characteristics of newly immobilized-, subsequently released-, and residual-N were studied in soils receiving KNO₃ labelled with ¹⁵N together with glucose, straw, and cellulose.

Immobilization of nitrogen proceeded rapidly and reached its maximum at incubation periods of 3 days to 8 weeks or more, varying with the kind of carbon sources added. Following the maximum tie-up of nitrogen a rapid release began. After 20 weeks the immobilized nitrogen was released at a considerable rate for each carbon source.

At the period of maximum immobilization of nitrogen added to soil there was a clear difference in the percentage distribution of various forms of organic nitrogen between applied-N and native-N. The former was higher in amino acid N and unidentified N and lower in nonhydrolyzable N than the latter, and almost the same in hexosamine N and ammonium N as the latter.

With regard to all carbon sources the principal form of organic nitrogen contributing to mineralization was amino acid N and its susceptibility to mineralization was much higher in the applied-N than in the native-N, and further, the susceptibility of hexosamine N to mineralization was considerably lower than amino acid N.

In view of these results, it was presumed that a major origin of the amino acid N contributing to the mineralization process might be peptide complex substances such as mucopeptides and structural proteins, which originate from the microbial cell walls remaining in soil as a residual nitrogen of newly immobilized-N.