Based on biological incubation experiments, Yuanyang terraced paddy soils were selected to study the characteristics of nitrogen (N) nitrification with three altitudes (high altitude: 1 626～1 672 m, medium altitude: 1 532～1 537 m and low altitude: 1 445～1 459 m) and three soil layers (0～30 cm, 30～60 cm and 60～90 cm). The results showed that for the two treatments (CK and the N added treatment), the net nitrified nitrogen amount did not show an obvious change during the early period (20 days), but increased sharply during the later period (20～70days). The nitrification ratio was less than 44% during the 70 days incubation, indicating that the nitrification capacity was weak. It showed that the anaerobic condition in the field inhibited the capacity of nitrification in Yuanyang terrace. The amounts of net nitrified N in different soil layers were 0～30 cm30～60 cm60～90 cm during the 70 days incubation, and there were no significant differences among the three altitudes. There were no significant difference in the amount of net nitrified N between the CK and the nitrogen added treatment, indicating that the soil autotrophic nitrification was weak and heterotrophic nitrification might be the dominant way of nitrification in Yuanyang terrace. There were significant linear relationships (P0.05) between the amount of net nitrified N with soil TOC, TN, DOC, DON, MBC, ROC and LFN contents.
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