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

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Abstract
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.