【作者】 杨伟；

【导师】 蔡崇法；

【作者基本信息】 华中农业大学 ， 资源环境信息工程， 2013， 博士

【摘要】 南方红壤丘陵区的水土流失问题是我国面临的重要环境问题之一。红壤富含粘粒和铁铝氧化物,土壤结构发育良好。团聚体是土壤结构的基本结构单元,可作为预测土壤抗侵蚀能力的良好指标。目前在土壤水蚀研究领域,团聚体稳定性多采用湿筛、震荡、模拟降雨等间接方法测定,难以定量化表达团聚体稳定性。团聚体力学指标是一种定量化表达团聚体稳定性的直接指标,能很好地指示土壤结构稳定性,已经被广泛应用于土壤耕作和风蚀研究领域。已有研究表明团聚体抗张强度与水稳性及土壤水蚀之间存在一定联系。本研究从湖北咸宁和江西进贤选取第四纪粘土和泥质页岩两种母质发育的不同利用红壤样品,从定位培肥试验选取同种红壤发育的不同有机质含量的土壤样品。原位测定土壤的抗剪强度和贯入阻力,室内分析团聚体水稳性和力稳性,比较团聚体水稳性和力稳性之间的关系。选取部分样品研究团聚体张力破碎和降雨破碎的特点,建立抗张强度与土壤侵蚀之间的联系。进而开展室内模拟坡面细沟间侵蚀试验,利用团聚体抗张强度预测红壤坡面细沟间速率。本研究的创新点和主要结论如下：1红壤团聚体稳定机制。对江西进贤和湖北咸宁两个地区泥质页岩和第四级粘土发育的不同利用红壤团聚体的研究结果表明,粘粒、CEC和铁铝氧化物是影响团聚体水稳性的主要因素,有机质和CEC是影响红壤团聚体抗张强度的重要因素。CEC与团聚体三种破碎机制均表现出显著相关关系,粘粒含量与团聚体消散破碎密切相关,晶型和非晶型铁铝氧化物与团聚体机械打击破碎和不均匀膨胀破碎有关。有机质和CEC与抗张强度均表现出显著相关关系。咸宁长期培肥试验的结果表明,有机质也是影响红壤团聚体水稳性和力稳性的重要因素。利用不同培肥措施改变团聚体有机质含量,研究有机质对红壤团聚体稳定性的影响。结果证实有机碳和热水溶性碳水化合物与团聚体降雨侵蚀过程的三种主要破碎方式均有密切关系,其关系紧密性依次为消散破碎>机械打击破碎>不均匀膨胀破碎。热水溶性碳水化合物与抗张强度有良好的正相关关系,而有机碳和抗张强度之间未发现明显关系。此外,有机碳和热水溶性碳水化合物还与团聚体容重与孔隙度、团聚体斥水性等性质密切相关,是指示培肥管理对表层土壤团聚体结构改变的良好指标。2团聚体抗张强度是表征红壤抗细沟间侵蚀能力的良好指标。抗张强度能从力或能量角度定量化表达团聚体稳定性,本研究以WEEP模型细沟间侵蚀方程为基础,结合室内模拟坡面降雨,在考虑径流和不考虑径流两种条件下分别建立了利用抗张强度预测红壤细沟间侵蚀速率的数学模型,其R2分别达到0.68和0.80。在该模型的基础上进一步引入团聚体斥水性指数对模型进行改进,提高了模型精度,改进后的模型在考虑和不考虑径流两种条件下R2分别达到0.74和0.86。3团聚体抗张强度与团聚体水稳性存在密切的关系。通过湿筛法研究发现,抗张强度与团聚体破碎后的>0.25mm水稳性团聚体含量呈极显著相关关系,与平均重量直径呈现显著相关关系。通过能区分团聚体不同破碎方式的LB法研究发现,抗张强度与团聚体消散破碎呈极显著相关关系,与机械破碎呈现显著相关关系,而与不均匀膨胀破碎之间没有明显的线性相关关系。4团聚体微结构是团聚体张力破碎和消散破碎的共同基础。通过观察降雨过程团聚体粒径分布的变化,消散是暴雨条件下红壤团聚体破碎的主导方式。根据脆性破裂理论和团聚体消散破碎机理,团聚体内部裂隙、孔隙等结构弱点的强度和分布决定了团聚体张力破碎和消散破碎过程。对于不同粒径团聚体,抗张强度与团聚体模拟降雨破碎后的标准平均重量直径之间存在显著的线性相关关系。对于不同土壤同粒径团聚体,抗张强度与团聚体模拟降雨破碎后的平均重量直径也存在显著的线性相关关系。5团聚体破碎和溅蚀分离具有粒径效应。团聚体粒径越大,侵蚀过程中抵御自身破碎的能力越弱,但是破碎后形成的颗粒越大,抵御径流和溅蚀搬运的能力越强。大团聚体溅蚀峰的出现有延迟效应,团聚体粒径越大延迟效应越明显,故而其溅蚀量越低。易碎性高的土壤不同粒径团聚体溅蚀分离速率差异较小,大团聚体的溅蚀延迟效应较小。溅蚀量主要受小团聚体稳定性的影响,易碎性高的土壤一般小团聚体较为稳定,因此溅蚀量较低,但是易碎性和溅蚀分离速率之间没有明显的线性函数关系。更多还原

【Abstract】 The soil erosion of the hilly red soil region in Southeast China is a most serious environmental problem of China. Aggregate is the basic unit of soil structure, so aggregate stability is a good indicator of soil resistance to erosion. Numerous methods have been developed to assess aggregate water stability, such as wet sieving, end-over-end shaking and water-drop impact, but a major limitation of these procedures is that they apply an arbitrary application of mechanical energy that is not quantified, resulting in a stability assessment that can only be related to the context in which it is being used. Ultrasonic technique provided a new way to assess aggregate stability. In theory, aggregate bond energy can be quantified by the ultrasonic aggregate stability assessment. However, there still some problems need to be solved in theory. Tensile strength is a quantitative aggregate index and very sentive to soil structure. It has been used widely in the studies of soil tillage and wind erosion. Some researchers have found the relationships between tensile strength and aggregate water stability and some erosion characteristics.However, there is still little information about the relationship between tensile and soil erosion.Therefore, objectives of this research were to (i) understand the stable mechanism of mechanical stability and water stability in Ultisols (Subtropical China),especially the effect of organic matter on aggregate stability;(ii) to compare the mechanism of aggregate breakdown in tension and the different mechanism of aggregate breakdown under rainfall (iii) to analyze the relationship between aggregate tensile strength and aggregate breakdown process;(iv) to explore the possibility of predicting soil detachment by interrill erosion in Ultisols (subtropical China).First, some typical Ultisols developed from Quaternary red clay and Shale were selected from Hubei Province and Jiangxi Province. First, aggregate tensile strength and water stability were compared, especially the relationship between tensile strength and different mechanism of aggregate breakdown during soil erosion process. Considering the confusion about the effect of organic matter on aggregate stability of Ultisols, we selected the same soils with different fertilizer management, which had the similar oxides content and soil texture, to analyse the relationship between organic matter and aggregate stability.Second, the process of different size aggregate breskdown under rainfall was observed.We analysed the compared the process of aggregate breakdown in tension and the process of breakdown in erosion. The relationship between tensile strength and these indexes of aggregate breakdown, such as particle size distribution and splash detachment, were analysed as well. In addition, we discussed the relation between friability and soil erosion.Third, we analysed the breskdown process of3-5mm aggregate from different soil under rainfall, and compared these relationships between soil erosion indexes (size distribution and splash detachment) and aggregate stability indexes, including aggregate water stability, tensile strength and friability.At last, laboratory experiments of simulated rainfall involving three different slope wereconducted on six Ultisols to evaluate the possibility for assessing interrill erosion rates for the subtropical Chinese Ultisols by tensile strength.The main results were listed as following:1According to the research of aggregate from different parent material and different land use, soil texture and oxides of which varied greatly, cation exchange capacity, clay content and oxides were the most important stable factors contributed to aggregate water stability, whereas cation exchange capacity and organic matter were the most important stable factors contributed to tensile strength.According to the research of different fertilizer management, organic matter is a strong determinant of tensile strength and aggregate water stability in soils with similar soil texture and oxides content. Organic carbon and hot water extractable carbohy were related to the three mechanisms of aggregate breakdown, aggregate repellency and other aggregate propertirs significantly. They are good indexs of the effect of fertilizer management on aggregate stability.2On the basis of WEPP erosion model, we developed two prediction equations for assessing interrill erosion rate by incorporating the reciprocal of aggregate tensile strength in the prediction evaluations for soil erodibilites, both of which had high efficiency in assessing soil detachment rate in interrill erosion in our study. R2of the equations with runoff and without runoff were0.68and0.80, respectively. To further improve the efficiency in prediction, water-repellency index was introduced in the two prediction equations, which enhances more precision of two prediction equations. R2of these new equations were0.74and0.86, respectively.3Tensile strength is closely related with aggregate water stability. The results of wet-sieving method, including the content of water stable aggregate and mean weight diameter, showed good correlation with tensile strength. For the three aggregate breskdown mechanisms in erosion, both breakdown caused by slaking and by differential swelling showed significant correlation with aggregate breakdown in tension, especially for aggregate breakdown caused by slaking, which showed very significant correlation with.tensile strength.4Both aggregate break in tension and break in slaking were depended on aggregate microstructure. Under the simulated rainfall with60mm/h intensity, slaking is the dominant mechanism of aggregate breakdown. As a result, aggregate breakdown during rainfall was closely related to tensile strength. For different size aggregates, good correlations were observed between tensile strength and normalized mean weight diameters under different amounts of cumulative rainfall. For the same size aggregates of different soils, good correlations were observed between tensile strength and mean weight diameters under different amounts of cumulative rainfall.5As aggregate size increased, the resistance to aggregate breakdown was decreased whereas the resistance to detachmen t was increased. The rates of splash exhibited delayed detachment peaks with the larger-size aggregates and that the delay became greater as the initial aggregate size increased. For two soils with different frisbility, the tendency that aggregate splash decreased with increasing aggregate size was more obvious for the soil with low friability. Because splsh detachment is mainly affected by the tensile strength of small aggregate, for all size classes, the aggregates of soil with low friability produced more splash materials. However, no significant linear relationship between friability and the amount of splash or mean weight diameters after rainfall were observed.At alst, tensile strength is a quantitative aggregate stability index, which can be determined by simple tests, used for aggregates of very different size, and is very sensitive to soil structure. Considering the main problems of other methods for testing aggregate stability, it was concluded that these formulae based on the aggregate tensile strength have the potential to assesse intertill erosion rates for the subtropical Chinese Ultisols.更多还原