Organic carbon and total nitrogen dynamics of reclaimed soils following intensive agricultural use in eastern China

In past decades, coastal tidal flats in China have experienced rapid and extensive agricultural reclamation due to the increasing pressure of population growth. With more coastal land likely reclaimed in the future, an increase in the understanding of the effects of the reclamation history and changes in land use on soil properties is essential. In this study, a total of 746 surface soil/sediment samples were collected from three study areas with different reclamation durations and land use patterns on the coasts of Dafeng, Rudong and Cixi in eastern China, covering a total area of 1926 km2. The results showed that mean soil organic carbon (SOC) and soil total nitrogen (STN) in the three study areas differed slightly and ranged from 7.24 to 7.69 g kg−1 and from 0.71 to 0.76 g kg−1, respectively. SOC and STN increased significantly with an increase in reclamation duration in all of the study areas, except for the early stage of land conversion in Cixi and the late stage of conversion in Dafeng, which highlighted that the accumulation of SOC and STN was positively correlated with reclamation duration. In Dafeng and Rudong, land dominated by human uses had much higher levels of SOC and STN than those in the tidal flats. For the same duration of reclamation, paddy land had higher levels of SOC and STN than those in the upland, with the exception of the 10-year-old land in Cixi. Our results also indicated that reclaimed coastal soils can sequester considerable amount of OC through improved land management. The differences in the sequestration potential for OC and the dynamics of SOC and STN among the three chronosequences were attributed to specific land use patterns in each study area.