Factors affecting immobilization and release of nitrogen in soil and chemical characteristics of the nitrogen newly immobilized IV. Chemical nature of the organic nitrogen becoming decomposable due to the drying of soil

This study deals with the effect of air-drying or oven-drying a soil and remoistening it on the flush of decomposition of soil organic nitrogen and with a comparison of the chemical nature of the nitrogen mineralized between the newly immobilized nitrogen in a soil receiving glucose and KNO3 labelled with 15N and the native organic nitrogen in the soil. Mineralization of soil organic nitrogen was remarkably accelerated through the effects of both air-drying and oven-drying, and the effect was much greater in the latter than in the former. The immobilized-N was made much more susceptible to mineralization than the native-organic N through the effect of air-drying or oven drying. In the course of mineralization of the native-organic N, air-drying enhanced the decrease of amino acid N, in particular after 6-weeks incubation. Also, oven-drying intensified the decrease of all the forms of N for the same incubation periods; the decrease was most remarkable in the forms of amino acid N, unidentified N, and hydrolyzable ammonium N. In the course of mineralization of the immobilized-N, air-drying heightened the decrease of unidentified N, in particular, and, to a slight degree, of amino acid N and hexosamine N after 6-weeks incubation. Oven-drying enhanced the decrease of all the forms of N for the same incubation period; the decrease was most remarkable in unidentified N. Hexosamine N also showed a substantially high susceptibility to mineralization through the effect of oven-drying the soil. From these results it is certain that the principal organic nitrogen compounds becoming decomposable through the drying effect belong to the peptide complex substances.