Estimation of the content and renewal rate of nitrogen from the active soil phase in an experiment with N-15-labeled fertilizers

The N content of mineral, microbial, and metabolic pools, which comprise th e active phase of soil nitrogen was estimated in pot experiments with cross application of N-15-labeled and nonlabeled NH4NO3 on N-15-labeled and nonl abeled chernozem, gray forest, and soddy-podzolic soils. The active phase c ontains 9-14% of the bulk N amount, being highly dynamic and renewable. Fro m 48 to 86% of N in this phase was renewed during 115 days of the experimen t. Application of N fertilizer and cultivation of plants accelerated and in tensified the renewal of N of the active soil phase.