Estimating the spatiotemporal variations and driving factors of farmland soil organic carbon density (SOCD) is of great significance for enhancing soil carbon sequestration capacity. Herein, a large region of complex topography was targeted, which includes hill–mountain, valley–basin, and plain–platform. Based on the massive amounts of sampling data (57,254 measured values) and a large-scale soil map of 1:10,000 (371,976 polygonal patches), the gravity center migration model and gray correlation model were used to quantify the spatiotemporal variations and driving factors of farmland SOCD. The results indicated that the farmland soils in the study area had dual functions of carbon source and sink during 1982–2018, of which 45.50 % and 54.50 % were identified as carbon source and sink, respectively. Specifically, the SOCD for the entire study area, its hill–mountain, and valley–basin increased from 2.79 kg m, 2.97 kg m, and 3.06 kg m to 2.87 kg m, 3.06 kg m, and 3.14 kg m, respectively, with 0.08 kg m carbon sequestrations and a northeast migration direction for the SOCD gravity center (angle: 21.94°, 23.56°, and 18.82°; distance: 1.56 km, 2.73 km, and 3.20 km). There was a smaller increase of 0.07 kg m in SOCD for the plain–platform from 2.38 kg m (1982) to 2.45 kg m (2018), and the SOCD gravity center migrated to the southwest with an angle of −172.46° and a distance of 1.84 km. Thus, the spatiotemporal variations of farmland SOCD in various landforms varied greatly. Over the past 36 years, SOCD variations were driven by a combination of intrinsic soil factors and external factors such as human disturbance. However, the driving effects of these factors on the landforms of hill–mountain, valley–basin, and plain–platform were quite different in size and order. Therefore, we suggest that topography must be considered when formulating policies to improve soil carbon sequestration, and priority should be given to landform-specific SOCD variation and the factors contributing to them.

中文翻译：

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复杂地形不同地貌农田土壤有机碳时空变化及驱动因素


估算农田土壤有机碳密度（SOCD）时空变化及驱动因素对于增强土壤固碳能力具有重要意义。这里的目标是大片复杂地形区域，包括丘陵-山地、山谷-盆地和平原-台地。基于海量采样数据（57,254个实测值）和1:10,000大比例尺土壤图（371,976个多边形斑块），利用重心迁移模型和灰色关联模型量化了土壤污染时空变化和驱动因素。农田 SOCD。结果表明，1982—2018年研究区农田土壤具有碳源和碳汇双重功能，其中分别有45.50%和54.50%被确定为碳源和碳汇。具体而言，整个研究区及其丘陵山区和谷地盆地的SOCD分别从2.79 kg m、2.97 kg m和3.06 kg m增加到2.87 kg m、3.06 kg m和3.14 kg m。固碳量0.08 kg·m，SOCD重心向东北迁移（角度：21.94°、23.56°、18.82°；距离：1.56 km、2.73 km、3.20 km）。平原台地SOCD由1982年的2.38 kg·m增加到2018年的2.45 kg·m，增幅较小，增加了0.07 kg·m，SOCD重心向西南方向迁移，角度为-172.46°，距离为1.84 公里。由此可见，不同地貌农田SOCD的时空变化差异较大。在过去的36年里，SOCD的变化是由土壤内在因素和人类干扰等外部因素共同驱动的。但这些因素对丘陵-山地、河谷-盆地、平原-台地地貌的驱动作用大小和顺序差异较大。 因此，我们建议在制定土壤碳汇改善政策时必须考虑地形因素，并优先考虑特定地形的SOCD变化及其影响因素。