|Alternative Title||Depth-stratigraphy of SOC, N, P at Landscape Positions under Soil Redistribution by Tillage and Water Erosion|
|Place of Conferral||北京|
|Keyword||有机碳 土壤养分 土壤侵蚀 耕作侵蚀 水蚀|
|Abstract||紫色土丘陵区是我国水土流失最为严重的地区之一，坡耕地水土流失严重威胁着水土资源的可持续利用。本研究选择2个试验区，分别位于四川盆地中部的简阳市和三峡库区腹地的重庆市忠县，从耕作类型上设置了顺坡耕作（水蚀占主导、耕作侵蚀占主导、耕作侵蚀和水蚀并重）、逆坡耕作和退耕3种类型坡地，并且从地貌类型上设置了线性坡和复合坡2种坡地作为研究对象。采用137Cs示踪、物理示踪、模拟耕作、模型预测、地统计学分析及数理统计分析相结合的方法，系统研究了紫色土坡地土壤侵蚀对不同坡位土壤碳氮磷深度成层性的作用机制。主要结果和结论包括： 1、坡面土壤侵蚀空间分布格局 在坡梯地景观，顺坡耕作坡地土壤再分布的模式是：坡顶和肩坡以耕作侵蚀为主、背坡和坡脚以水蚀为主，然而坡趾土壤侵蚀/沉积却取决于耕作侵蚀与水蚀的不同组合模式。坡趾可能出现三种情况：当耕作沉积显著大于水蚀时，土壤明显沉积；当耕作沉积与水蚀相当时，土壤侵蚀/沉积微弱；当耕作沉积显著小于水蚀时，土壤强烈侵蚀。逆坡耕作坡地土壤再分布模式与顺坡耕作不同：逆坡耕作引起土壤向上坡移动，导致坡底部发生耕作侵蚀，在上坡累积；而水蚀导致土壤在坡趾沉积。 2、耕作侵蚀作用下土壤碳氮磷空间变异性 137Cs数据显示耕作不仅导致土壤向下坡传输，而且导致不同坡位土壤的垂直混合。模拟耕作后，土壤剖面在坡顶完全消失，而在坡趾显著增加。15年耕作后线性坡和复合坡母岩裸露面积占研究坡地的16.0%和7.6%。土壤碳氮磷随着坡顶土壤剖面的消失而损失，在坡面底部明显累积。土壤碳氮磷储量的变异性随着耕作强度的增加而增强，表明耕作导致土壤向下坡传输突出了土壤剖面性质在顺坡方向上的变异性。土壤碳氮磷浓度的垂直变异性随着耕作强度的增加而减小，表明耕作的混合作用弱化了土壤性质在垂直方向上的变异性。 3、耕作侵蚀与水蚀共同作用下土壤碳氮磷迁移 耕层土壤有机碳浓度在水蚀为主导侵蚀过程的坡耕地不同坡位的差异显著；而在耕作侵蚀为主导侵蚀过程的坡耕地无显著差异。土壤全氮的分布与有机碳相似。耕层土壤全磷浓度在上述两种类型的坡耕地都呈现出从坡顶向坡趾显著增长的趋势。耕层土壤速效磷浓度在水蚀为主导侵蚀过程的坡耕地从坡顶到坡趾显著增加，而在耕作侵蚀为主导侵蚀过程的坡耕地不同坡位速效磷浓度基本一致。土壤碳氮磷的顺坡分布格局与耕作侵蚀和水蚀的不同组合模式密切相关。 耕作侵蚀区土壤有机碳和全氮垂直变化速率明显高于耕作沉积区。不同坡位的土壤全磷垂直变化速率基本一致，这主要归因于耕作侵蚀导致土壤全磷在侵蚀区的补充效应减弱了土壤全磷的垂直变化。水蚀为主导侵蚀过程的坡耕地土壤速效磷垂直变化速率的绝对值从坡顶到坡趾显著减小；而耕作侵蚀为主导侵蚀过程的坡耕地不同坡位速效磷垂直变化速率基本一致，显示了水蚀和耕作侵蚀对土壤速效磷垂直分布的不同作用机制。 4、土壤保护措施对土壤碳氮磷分布和动态的影响 退耕坡地上坡土壤C/N较耕作坡地土壤增大，显示出退耕前土壤侵蚀严重的上坡具有很强的固碳潜力。景观因子（坡长、坡度）对退耕坡地土壤有机碳分布的影响不明显，这有助于有机碳的固定。耕地转变为草地能够显著增加土壤有机碳储量（后者较前者平均增加25%）。 长期（29年）逆坡耕作，总土壤侵蚀速率比顺坡耕作坡地显著减小（60.5%）。相对于顺坡耕作，逆坡耕作坡地土壤碳氮磷显著累积，这主要归因于水蚀与耕作侵蚀的特定组合产生的土壤再分布模式变化；当耕作导致的土壤移动方向与水蚀导致的土壤移动方向相同时，加速了土壤碳氮磷的流失，而两者方向相反时能够增加土壤碳氮磷的累积。逆坡耕作累积的土壤有机碳、全氮和全磷主要贮存在耕层以下，而速效磷主要贮存在耕层。逆坡耕作对减小土壤侵蚀和土壤养分流失作用明显，改变传统的耕作方向可以作为重要的土壤可持续管理战略。|
|Other Abstract||Soil erosion is a major threat to sustainable use of soil and water resources, and exerts an influence on soil properties which soil quality and crop yield depend on. The hilly area of purple soil is one of the most serious soil erosion areas in China. Seven sloping cultivated landscapes were selected from two sites located in Jianyang County, Sichuan Province, and Zhongxian County, Chongqing Municipality, respectively. The objective of this study was to determine effects of soil redistribution rates and processes on depth-stratigraphy of soil organic carbon (SOC), total nitrogen (N), phosphorus (P) and extractable P among landscape positions. This study used 137Cs tracing，physical tracing, consecutive tillage by hoeing, model prediction, and geostatistics analyses as well as traditional analyses. The main results and conclusions are as follows:|
Spatial distribution pattern of soil erosion along the transect of slopes
The general patterns of soil redistribution by tillage and water were analyzed for downslope tillage (DT) site. Tillage erosion was mainly responsible for soil loss at the
summit and shoulder slope positions, while water erosion played a primary role in soil loss at the backslope and footslope positions, whereas soil erosion/deposition depended on different combination patterns of tillage erosion with water erosion at the toeslope position. Three possible cases may occur at the toeslope position. When tillage deposition was greater than water erosion, obvious soil deposition occurred; when tillage deposition and water erosion were approximately equal, the till layer was only replaced but not decreased; when tillage deposition was obviously less than water erosion, serious soil erosion occurred. The pattern of soil redistribution by water and tillage for the upslope tillage (UT) site is remarkably different from the DT site. The upslope tillage moved soil uphill, resulting in soil accumulation at upper slope positions and soil loss at lower slope positions, while water erosion delivered soil to the bottom position and deposited at the toeslope position. The process of UT led to a hollow at the toeslope position, which acted as an effective water and sediment trap and could make a significant contribution to reduced soil export.
Spatial variation of SOC, N and P as affected by tillage erosion
The 137Cs data showed that intense tillage caused the soil vertical mixture and ownslope transport. After intense tillage, the soil profile disappeared on the slope summit due to intense soil downslope translocation, while a thickened soil profile was present in toeslope positions, where the original soil profile was buried. Soil profile disappeared at the summit slope boundary, with the exposure area of 16.0% and 7.6% of the experimental plot after 15 tillage operations, respectively, for the linear and complex slopes. SOC was completely depleted with the disappearance of soil profiles at the summit position, while a substantial increase in SOC inventories of the post-tillage soil profile was found in the toeslope position. Changes in total N, P and extractable P inventories of the post-tillage soil profile exhibited a pattern similar to that of SOC inventories. The variation of soil profile properties increased with tillage time, suggesting that the downslope transport of soil induced by tillage accentuates the variability of soil properties in the lateral direction. The gap and variation in soil constituents between the till layer and sublayer declined with increasing tillage intensity, suggesting that the mixing effect of tillage attenuates the variability of soil properties in the vertical direction. Movement of SOC, N and P under the combination of tillage erosion with water erosion
On the sloping cultivated lands where soil redistribution is mainly the result of water erosion, differences in SOC concentrations in the till layer were highly significant among
landscape positions. In contrast, for the sloping cultivated lands where tillage erosion is the dominant process, no significant differences in SOC concentrations was observed among the landscape positions. Distribution of total N concentrations exhibited a pattern similar to that of SOC concentrations. Total P concentration in the till layer on the two kind of lands increased from the summit to toeslope position. However, the distribution characteristics of extractable P differed markedly from that of total P. The differences in extractable P concentrations in the till layer were highly significant among different positions on the sloping cultivated lands dominated by water erosion process, while no significant differences in extractable P concentrations in the till layer were observed among different positions on the sloping cultivated lands dominated by tillage erosion process. These results suggested that distribution of SOC, N and P along the transect of the slope were related to different combination patterns of tillage erosion with water erosion.
The vertical changing rate per unit distance (VCR) along the vertical direction in SOC
and N concentrations varied with landscape positions. The absolute values of VCR in SOC and N in the erosional areas were higher than those of the depositional areas, showing that tillage erosion resulting in differentiation of SOC and N depth distribution at different landscape positions. The VCR in total P showed unobvious change among summit, middle and toeslope positions, suggesting that the complement effects of total P in the tillage erosion areas resulted in decreasing vertical change of total P. Unlike the vertical distribution of total P, the absolute value of VCR in extractable P showed a significant decrease trend from summit to toeslope on the sloping cultivated lands dominated by water erosion process, while no apparent changes in the VCR in extractable P were observed at different slope positions on the sloping cultivated lands dominated by tillage erosion process, indicating that the effect of water-induced soil redistribution on vertical change of extractable P differed significantly from that of tillage-induced soil redistribution. Effects of soil conservation measures on distribution and dynamics of SOC, N and P SOC inventories in this soil layer significantly increased after conversion from cultivated land to grassland, with a mean increment of 25%. In upper slope positions, converted soils (especially in 0-5 cm surface soil), exhibited a wider C/N ratio than cultivated soils, implying that a strong characteristics of SOC sequestration exists in upper slope areas where severe soil erosion occurred before land conversion. It is suggested that landscape factor impacts on SOC spatial distribution become insignificant after conversion of cultivated land to grassland, which is a conducive effect on the immobilization of organic carbon. These results suggested that conversion of cultivated land to grassland can remarkably increase SOC stocks in soil, especially improve the potential of SOC sequestration in the surface soil in a moderate period
The total erosion rate decreased by 60.5% after 29 years of UT compared to DT. SOC,
total N, P and extractable P inventories at the UT site increased significantly compared with those at the DT site. It is suggested that soil movement by water and tillage erosion occurred in the same direction accelerates the depletion of nutrient pools, whereas the opposite direction of soil movement for the two can increase nutrient accumulations. SOC, total N and P were stored below the till layer, and extractable P was stored in the till layer for UT. These results suggest that UT has significant effects for diminishing soil erosion and nutrient loss on sloping land, and the change in tillage direction is a feasible alternative for the development of sustainable soil management strategy.
|李富程. 土壤侵蚀作用下不同坡位碳氮磷深度成层性研究[D]. 北京. 中国科学院研究生院,2013.|
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