3-6. Net nitrification and net nitrogen mineralization rates
Figure 3-17 shows the net nitrification and the net nitrogen mineralization rates in the soils of the Hyakumakidani watershed at each temperature in 2002, 2019, and 2023. In 2019, the net nitrogen mineralization rate at 30°C showed a particularly high value, and it was much higher than the net nitrification rate. Comparing the net nitrification rate, no significant changes were observed between 2002 and 2023. The potential to produce nitrate has been unchanged for 20 years. Similar values in net nitrification and net nitrogen mineralization rates, which were characteristic of Stage-3 nitrogen saturation according to Aber’s prediction, reflect that the Hyakumakidani watershed is considered to remain in Stage-3 nitrogen saturation.