【作者】 闫峰陵；

【导师】 蔡崇法； 史志华；

【作者基本信息】 华中农业大学 ， 土壤学， 2008， 博士

【摘要】 我国南方红壤丘陵区水热资源丰富,在农业生产和经济发展中占有重要地位。针对该地区严重的土壤侵蚀退化,开展红壤结构特征与坡面侵蚀过程互馈机理研究,并就二者定量关系进行探讨,对合理利用红壤资源具有重要意义。本文基于团聚体破碎理论,以我国中亚热带丘陵区第四纪红粘土、花岗岩和泥质页岩等典型母质发育红壤为研究对象,通过控制土壤湿润速度、初始水分含量和降雨特征等条件,系统分析了降雨条件下红壤表土团聚体的破坏过程、机理,以及侵蚀过程响应。此外,以野外原位试验数据为基础,定量研究了红壤坡面侵蚀、入渗与团聚体稳定性关系,揭示了土壤团聚体破碎机理与坡面侵蚀过程之间的内在联系。取得的主要结论有:1、在采用传统湿筛法指标衡量团聚体稳定性的基础上,结合能区分降雨条件下团聚体破碎方式的LB法,从不同角度对团聚体的稳定性作了评价;运用相对消散指数（RSI）和相对机械破碎指数（RMI）区分了红壤团聚体对不同破碎机制的敏感性。同时,针对红壤独特的成土条件及理化性质,分析了坡耕地条件下影响红壤团聚体稳定性的主要因素及其作用机制,其中对粘粒、铁铝氧化物和有机质与团聚体稳定性之间关系进行了重点探讨。（1）红壤团聚体稳定性特征。湿筛法与LB法测定团聚体稳定性结果均表明:第四纪粘土红壤团聚体稳定性最高,花岗岩红壤次之,泥质页岩红壤团稳性最低;不同初始粒径团聚体稳定性不同,在不同处理中,总体趋势是团聚体的初始粒径越小,稳定性越高。（2）红壤团聚体稳定机制。不同破碎机制中,所有土壤团聚体稳定性排序均为快速湿润＜预湿振荡＜慢速湿润。其中,第四纪粘土红壤对消散作用较为敏感,花岗岩红壤对机械破碎作用较为敏感,泥质页岩红壤对上述两种作用均很敏感。可见,快速湿润引起的消散作用和外界应力引起的机械振荡作用,是红壤团聚体破碎的主要机制。（3）红壤团聚体稳定性与土壤性质关系。红壤团聚体稳定性与土壤有机质、腐殖酸含量及其组成之间相关性较低,与铁铝氧化物及粘粉粒含量之间呈显著正相关,说明在有机质含量较低的红壤中,无机胶体在保持团聚体稳定性上起主导作用;土壤中粘粒一方面作为胶结物质能增强团聚体稳定性,另一方面能增强湿润过程消散作用而降低团聚体稳定性。此外,腐殖酸含量及其组成与PAD＞2mm（团聚体分散度）呈显著负相关,说明腐殖酸对较大粒径团聚体的形成及稳定机制有重要作用。2、基于团聚体破碎理论,通过控制湿润速度、初始粒径和降雨特征等条件,研究了降雨条件下红壤表土团聚体的破坏过程、结果和机理,探讨了团聚体稳定性及不同破碎机制对坡面侵蚀过程的影响;结合室内模拟试验结论,通过比较团聚体稳定性表征参数与坡面侵蚀过程相关性程度,首次提出针对侵蚀机理的红壤团聚体稳定性特征新指标—K_a。（1）快速湿润引起的消散作用对侵蚀过程影响。所有供试土壤中,径流强度随湿润速率增大而增大;不同粘粒含量土壤对湿润速率响应过程不同,粘粒含量越高,消散作用越明显,产流强度越小;粘粒含量越低,消散作用越小,产流强度越大。产沙过程中,除土壤GT2外,湿润速率对其它土壤坡面侵蚀率均有显著作用。相较于坡面产流过程,侵蚀率受团聚体稳定性与湿润速率的影响更为明显。快速湿润处理中侵蚀泥沙＜0.25mm颗粒所占比例较高,平均重量直径小于慢速湿润处理,这与表土结皮层的形成有关。（2）雨滴打击引起的团聚体机械破坏作用对侵蚀过程的影响。在团聚体稳定性较低、对机械破碎作用敏感的红壤中,雨滴打击对径流的影响主要是由土壤表层团聚体结构的破坏引起的;而在团聚体稳定性较高、对机械破碎作用不甚敏感的红壤中,雨滴打击对径流的影响主要表现为对表层土壤的压实作用。纱网覆盖处理侵蚀量均小于裸土降雨侵蚀量,但只有在团聚体稳定性较弱的红壤中二者差异达到显著。裸土条件下侵蚀泥沙MWD显著低于纱网覆盖处理,说明即使在团聚体稳定性较高的红壤中,雨滴击溅分散对泥沙的分选作用仍然较为显著。（3）不同粒径团聚体坡面侵蚀过程比较。团聚体粒径与径流强度和侵蚀量有很好的相关性,＜2mm团聚体的径流强度和侵蚀量均大于其它两种粒径;由于降雨过程中表土结构和排列紧实程度差异,＜2mm团聚体侵蚀泥沙的平均重量直径明显大于其它两种粒径。（4）本文中提出的团聚体稳定性特征值K_a,与坡面侵蚀过程参数呈显著或极显著相关;此外,K_a集合了团聚体对不同破碎机制的敏感性,具备较强的物理意义。可见,K_a不仅能够表征红壤团聚体稳定性的特殊性,而且在一定层面上解释了红壤侵蚀过程机理,是衡量红壤团聚体稳定性与可蚀性的良好指标。3、针对红壤丘陵区域严重的季节性干旱和水土流失现状,以团聚体破碎理论和本文室内研究结论为基础,对野外坡面侵蚀过程与团聚体稳定性关系进行了较为深入的探讨。结果表明,在野外尺度上红壤团聚体稳定性依然是影响坡面侵蚀的重要因素,并与径流强度、侵蚀率、入渗率、泥沙粒径等侵蚀参数显著相关。利用Horton入渗模型和WEPP细沟间侵蚀模型为框架,建立了侵蚀预测方程,结果显示新建立方程能较为准确的预测红壤坡面入渗量和侵蚀量。在侵蚀量预测方程中,不包含径流因子的方程式D_i=0.23K_aI²(1.05-0.85exp^-4sinθ)计算方法简单、结果可靠,具有更强的实用性和适用性。此外,该结论也扩展了团聚体稳定性特征参数作为土壤可蚀性指标的适用范围。更多还原

【Abstract】 Hilly red soil region are abundant in hydrothermal resources, and play an important role in agriculture and economy development. Improper land use and soil management, however, have caused severe soil erosion by water of red soils, and is one of the most important environmental problems in China. Analysis of soil structure characteristic and soil erosion is very important for comprehensive watershed management and sustainable development. Laboratory and field experiments of rainstorm simulations with different initial condition and rainfall characteristic were conducted on typical red soils derived from Quaternary red clay, Shale and Granite, and the soil aggregate stability was determined by the wet-sieving and LB-method. The improved formulae for assessing interrill erosion rate were established by incorporating the aggregate characteristic index in the prediction evaluations for soil erodibilites of red soils. The results of this study have promoted the development of soil erosion process research and provided scientific bases for the establishment of soil and water conservation in hilly red soil region. The main results were listed as following:1. The aggregates of selected red soils were used to understand the stability and the breakdown mechanisms by applying wet-sieving and LB-method. The relative slaking index （RSI） and the relative mechanical breakdown index （RMI） were used to determine the resistance to slaking and the mechanical breakdown of the soils of this study. Also, the relationship between aggregate stability and some soil properties, such as different forms of Fe oxides and Al oxides, organic matters, CEC and clay content were studied in condition of cultivated land.（1） The results of wet-sieving and LB-method indicated that the aggregate stability was highest in soils derived from Quaternary red clay, moderate in Granite, and lowest in Shale. There was some discrepancy in aggregate stability with different initial aggregate size, however, the stability of aggregate was found to be decreased with the increase of initial size in the selected soils.（2） The range of MWD （mean weight diameter） values differed widely, and values did not always show the same trend across the three treatments in LB-method. Across all three treatments, the MWD ranked in the order of fast wetting （FS）, Wet Stirring （WS）, and slow wetting （SW）. The MWD_FW and MWD_WS was more smaller than MWD_SW, indicating that the slaking and the mechanical breakdown were the main breakdown mechanisms in red soils. However, the vulnerabilities of slaking and mechanical breakdown were different in study soils. The soils derived from Quaternary red clay showed relatively high values in RSI and low in values RMI, while the soil derived from Granite showed a low RSI value and a high RMI value. The soils derived from Shale showed both high values in RSI and RMI.（3） Due to the subtropical conditions of red soil region, red soils were heavily weathered and characterized by enrichment of sesquioxide and poor in soil organic matter. Hence, the effect of soil organic matter and humus acid on aggregate stability was relatively weak, and clay content and sesquioxide were the most important bonding agents for aggregation of red soils. However, an increase in clay content in the soil might have two opposing effects on aggregate stability: （i） clay acted as a cementing material that holds particles together in aggregate and （ii） an increase in clay content could also increase slaking forces during soil wetting. Moreover, the parameter of PAD > 2 mm （percentage of aggregate disruption） was highly related to humus acid, indicating that humus acid was relatively important in formed processes of aggregates in large size.2. The study was designed to reveal the effects of aggregate breakdown mechanisms on interrill erosion dynamics. Based on laboratory experiments, the effects of slaking force, mechanical breakdown, and initial size of aggregate on the interrill erosion processes were discussed. A new aggregate instability index （K_a）, which could reflect the main mechanisms of aggregate breakdown in interrill erosion process, was proposed to measure the erodibility of red soils.（1） For all soils, the runoff rates followed the order slowing wetting （2 mm/h） < medium wetting （10 mm/h） < fast wetting （60 mm/h）. However, magnitude of changes in runoff rate depended on soil aggregate stability and texture. Based on runoff data, soils were divided into different groups lay on their response to wetting rate. The effect of wetting rate on runoff generation was significant in soils with high clay content while negligible in soils with low clay content. A significant effect of wetting rate on soil loss was found except soil GT2. The soil loss was affected by slaking and aggregate stability in two ways （runoff production and detachment）, and was more sensitive than runoff amount to wetting rate. The content of sediment fragment in diameter of < 0.25 mm was highest in the fast wetting treatment, also, the MWD was found to be lower than that in the slow wetting treatment, which was highly related to the form of surface sealing.（2） In present study, the runoff rate curves of all soils departed from each other evidently, indicting that the raindrop impact affected runoff generation essentially. The soils （SH2, GT1, and GT2） showed low aggregate stabilities and high susceptibilities to mechanical breakdown, and the aggregates of these soils were easily destroyed by rainfall impact to produce considerable fine particles. The aggregates in soil QT1, QT2, and SH1 were stable and could resistant the raindrop impact, however, the soil surface also became compacted. In this respect the main effect of rain impact was to produce sealing of the surface by redistributing already-detached material, rather than causing aggregate breakdown. The soil loss without raindrop impact was higher than that with raindrop impact, however, the difference between them was merely significant in soil with low aggregate stability. The MWD of sediment was significantly lower under raindrop impact, indicating that the dispersing effect of raindrop impact was essential on selecting sediment even though in soils with high aggregate stability.（3） Aggregate size <2, 2 to 3, 3 to 5 mm of each soil were exposed to simulated rainfall with an intensity of 60 mm/h. There was a significant interaction between soil loss, runoff rate and aggregate size. The results showed that as clod size increased, the runoff rate decreased. The small aggregate size was likely to form a seal, consequently, the soil loss increased with decreasing aggregate size. The largest MWD of sediment materials were found in aggregate size < 2 mm of each soil.（4） The new aggregate stability index （K_a）, reflected both the susceptibility of soil aggregates to slaking in sheet erosion as well as the detachment of soil material by raindrop impact. The simple correlation coefficients between the interrill soil loss and parameters of aggregate stability were calculated and the soil loss was found to be most strongly related to the new index, K_a. It could be thus supported that K_a was a suitable parameter to evaluate the interrill erosion in red soils with different rainfall conditions. However, all the erosion tests were accomplished in laboratory and the soil samples suffered the effect of sieving and rehandling. Therefore, the credibility of K_a to assess the interrill erosion needed to be validated in the field.3. Due to serious soil loss by water and seasonal drought in red soil region, this study was designed to investigate the relationship between aggregate stability and slope erosion. The result showed that the state of aggregate affected erosion process essentially, and aggregate stability was found to be highly related to runoff rate, erosion rate, and infiltration rate in the field scale. By introducing K_a into the WEPP model frame as a substitute for soil erodibility factor, statistical formulae for estimating soil loss were established with good correlation coefficient. It was concluded that these formulae based on the stability index, K_a, had the potential to improve methodology for assessing interrill erosion rates for the subtropical Chinese red soils. Considering the time-consuming and costly experimentation of runoff rate measurements, the equation without runoff rate,D_i =0.23K_aI²(1.05 -0.85 exp^-4sinθ) , was the more convenient and effective one topredict interrill erosion rates on red soils of subtropical China. These results extend the validation of soil aggregation characterization as an appropriate indicator of soil susceptibility to runoff and erosion in red soils, especially in subtropical China where intense rainfall is frequent. They also confirm that simple laboratory determination can provide data closely correlated with those resulting from more expensive or time-consuming field investigations.更多还原