Long-term excessive applications of chemical fertilizers may result in adverse impacts on soil functions. This study was to evaluate soil organic carbon (SOC) sequestration efficiency under continuous paddy rice cultivation with an excessive nitrogen (N) fertilization over the period from1980 to 2017 in South China. The SOC and total nitrogen (TN) of total 108 soil samples from continuous paddy soils and new paddy soils collected in 2017 were accordingly compared with those of 54 samples from paddy soils and upland soils obtained in 1980. Results show a total SOC increase of 0.79 g kg⁻¹ from the initial content of 12.82 g kg⁻¹ over a 37-year period despite an increased input of about 550 kg N ha⁻¹yr^-1 from fertilizers and 2000 kg C kg⁻¹ yr⁻¹ from all straw incorporation after 1990. This small C sequestration rate (or 0.021 g C kg⁻¹ yr⁻¹) was also observed to couple with a significantly elevated C:N ratio and badly weakened SOC-N correlation as of 2017, which is almost impossible to be revealed by normal fertilization experiments. The SOC sequestration rate of 0.145 g C kg⁻¹ yr⁻¹ of the new paddy soils that were developed from uplands since 1980 implies a declining tendency of SOC sequestration efficiency with rice cultivation time, which could be mainly attributed to both low soil N content and microbial activity rather than to SOC saturation. This case reminds of a need for more dedicated plot studies coupled with field observations on farmers’ routine fertilization practices to elucidate why the low soil N content remains with an excessive N fertilizer input and how N interacts with SOC in the continuous paddy soils.

长期过量施用化肥可能对土壤功能产生不利影响。本研究旨在评价 1980 年至 2017 年华南地区连续施氮（N）施肥水稻连续栽培土壤有机碳（SOC）的固存效率。将 2017 年收集的 108 个连续稻田和新稻田土壤样品的 SOC 和总氮 (TN) 与 1980 年收集的 54 个稻田和旱地土壤样品的 SOC 和总氮 (TN) 进行比较。 结果显示，总 SOC 增加了 0.79克千克^-1从12.82克千克的初始含量^-1在37年的期间，尽管约550公斤氮公顷的输入增加^-1年^-1来自肥料和 2000 kg C kg ^-1 yr ^-1来自 1990 年之后的所有秸秆掺入。还观察到这种小 C 封存率（或 0.021 g C kg ^-1 yr ^-1）与显着升高的 C:N 比和截至 2017 年，SOC-N 相关性严重减弱，这几乎不可能通过正常施肥实验来揭示。SOC 封存率为 0.145 g C kg ^-1 yr ^-1自 1980 年以来从高地开发的新稻田的 SOC 封存效率随水稻种植时间呈下降趋势，这主要归因于土壤 N 含量低和微生物活动，而不是 SOC 饱和。这个案例提醒我们需要进行更多专门的地块研究，并结合对农民常规施肥实践的实地观察，以阐明为什么在氮肥输入过多的情况下土壤 N 含量仍然很低，以及 N 如何与连续稻田中的 SOC 相互作用。