Abstract: Five subtropical paddy soils developed from different parent materials (reddish yellow clayey soil I, reddish yellow clayey soil II, granitic sandy soil, red clay soil, and alluvial sandy soil) were chosen, and samples were collected according to soil genetic horizons, aimed to investigate the profile distribution characteristics of dissolved organic carbon (DOC) in subtropical paddy soils, and to approach the profile shift patterns of DOC and related affecting factors. In the test soils, the DOC content in the profiles ranged from 13.61  to 90.34 mg·kg^-1. Plough layer had the highest DOC content (72.33 mg·kg^-1 on average), whereas the below layers showed relatively lower DOC content. Except for alluvial sandy soil, the DOC content in the other four soils did not decrease gradually with increasing depth, while had a higher distribution in some horizons (e.g., percogenic horizon, waterloggogenic horizon, and parent rock horizon) than in upper horizon, which could be related to the special leaching and deposition processes of DOC, its biological degradation, mineral phase adsorption, and the regimes of redox throughout the whole profile. The percentage of DOC to soil organic carbon (SOC) (DOC/SOC) in the whole profiles ranged from 0.21% to 1.31%, with the lowest value in plough layer and relatively higher values in below layers. It was suggested that the SOC in below layers could be more active and more sensitive to human disturbances (e.g., ploughup) than that in plough layer. Correlation analysis showed that there was a significant positive correlation between DOC and SOC, suggesting the decisive effect of SOC level in the profiles on the profile distribution of DOC. From the viewpoints of maintaining soil quality, sequestrating soil C, and mitigating soil CO₂ emission, it would be necessary to take different cultivation and management modes for different kinds of subtropical paddy soils.

Key words: slow/controlled release urea, ammonia volatilization, emission of N₂O., continuous application, paddy field