Vertical distribution and influencing factors of deep soil organic carbon in a typical subtropical agricultural watershed

Shunhua Yang, Yue Dong, Xiaodong Song, Huayong Wu, Xiaorui Zhao, Jinling Yang, Songchao Chen, Jo Smith, Gan-Lin Zhang

Research output: Contribution to journalArticlepeer-review

9 Citations (Scopus)


Soil organic carbon is one of the most commonly used indicators of soil health, as it plays a vital role in maintaining fertility and combating global warming. Understanding the vertical distribution and controlling factors of organic carbon in the entire regolith, rather than just the routinely defined upper 1 m portion of the soil, is crucial for assessing soil health in a holistic perspective. In this study, 21 boreholes in four different land uses were drilled from the land surface down to the bedrock in a typical subtropical agricultural watershed. The total organic carbon stock in the regolith ranged from 77.8 Mg C ha-1 to 311.8 Mg C ha-1 and the organic carbon content showed a progressive decline from land surface to bedrock. However, on average, only 19.0% of total organic carbon was stored at the depth 0–30 cm and 17.7% between 30 and 100 cm, whereas 63.3% was stored below 100 cm. Total organic carbon stock was significantly higher under paddy fields than under cropland, orchard or woodland in the upper 100 cm (p  0.05). According to the boosted regression tree analysis, soil texture outperformed the other edaphic factors and was the primary edaphic factor controlling TOC content of the different soils. The results show that there is a large carbon reservoir in the deep regolith. Land use strongly affects the distribution of carbon in the top 100 cm soil layers but has little effect on deep soil organic carbon. Deep TOC were closely linked to soil texture. This study highlights the importance of deep soil organic carbon for soil health and understanding the factors controlling its content for improved estimates of soil carbon storage.
Original languageEnglish
Article number108141
Number of pages12
JournalAgriculture Ecosystems & Environment
Early online date22 Aug 2022
Publication statusPublished - 1 Nov 2022

Bibliographical note

This study was financially supported by the National Key Research and Development Program of China (2018YFE0107000), the National Natural Science Foundation of China (42107334), the Second Tibetan Plateau Scientific Expedition and Research Program (2019QZKK0306), and the China Postdoctoral Science Foundation (2021TQ0337, 2021M703305). Special thanks go to our colleagues of Soils in Time and Space team for their help during field survey and laboratory analysis.


  • Deep soil organic carbon
  • Vertical distribution
  • Edaphic factor
  • Land use
  • Earth’s critical zone


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