【作者】 李朝霞；

【导师】 蔡崇法； 刘凡；

【作者基本信息】 华中农业大学 ， 土壤学， 2005， 博士

【摘要】 土壤侵蚀已成为我国中亚热带红壤丘陵区土壤退化的重要形式,是该地区农业可持续发展的主要制约因素之一,研究红壤侵蚀过程和机理对于区域土壤侵蚀防治、生产发展和环境保护有重要意义。降雨侵蚀过程中,降雨和径流为这一过程提供能量,土壤是作用的对象,因此,侵蚀过程与土壤自身性质相互作用是认识降雨侵蚀机理的一个重要环节。本研究以鄂南丘陵区第四纪粘土、花岗岩和泥质页岩发育的红壤为研究对象,应用室内分析和模拟降雨方法研究了降雨过程中表土结构变化和坡面侵蚀过程,在此基础上,系统分析了表土结构变化与坡面侵蚀过程之间的内在联系,获得以下结果: 第一,应用湿筛法,LB(Le Bissonnais)法和单雨滴打击法系统研究了土壤结构的稳定性,分析它与土壤相关性质的关系。结果表明:测定方法和衡量指标不同,土壤稳定性排序不同;土壤中不同形态的铁铝硅氧化物是保持土壤结构的主要胶结因子,有机质对团聚体的稳定作用并不明显。 湿筛法对不同母质红壤团聚体稳定性测定结果是:花岗岩>第四纪粘土>泥质页岩。对同种母质红壤,依侵蚀程度不同,第四纪粘土红壤结构稳定性是中度>强度>轻度,花岗岩红壤则是轻度>中度>强度。土壤稳定性颗粒分布因土壤而异,花岗岩红壤中>5mm和2-5mm的稳定性颗粒高达40%以上,泥质页岩红壤<0.25mm稳定性颗粒达到65%以上,第四纪粘土红壤稳定性颗粒分布差异较大,>0.25mm颗粒分布范围为36%～86%。总的表现是稳定性较高的土壤其稳定性大颗粒含量较多,泥质页岩和第四纪粘土红壤的稳定性是通过团聚体的水稳性体现,而花岗岩红壤则是含有较多较大粒径的砾石。 LB法研究结果表明降雨条件下土壤团聚体的破坏机制首要的是干土快速湿润导致的团聚体内部空气爆破而破坏,其次是外力作用(反复振荡)和缓慢湿润过程对土壤团聚体的破坏。不同破坏机理下团聚体的破坏强度为快速湿润<机械振荡<慢速湿润处理,且团聚体的稳定性随团聚体粒径减小而增大。 本研究土壤有机质含量较低(小于20.0g/kg),土壤团聚体稳定性与Fe_d,Al_d,Al_o,Si_o和clay%之间存在显著或极显著正相关关系,但与有机质,pH,CEC以及铁铝硅氧化物的活化度之间相关关系不明显。 第二、首次系统研究了土壤侵蚀与土壤表面结构的相互关系,并借用数字图像处理技术对侵蚀过程中表土孔隙的大小、形状、面积百分比等微形态特征进行了研究和探讨。侵蚀过程中,表土结构变化因土壤不同存在一定差异。泥质页岩红壤易形成结皮且结皮厚度及致密程度随降雨时间延长不断增加;轻度侵蚀的第四纪粘土红壤表土结构较易破坏并形成结皮,但发育程度较差,处于形成-破坏-形成的交替过程中,中度和强度侵蚀的第四纪粘土红壤表土结构稳定性较强,大团聚体破坏较更多还原

【Abstract】 In Hilly red soil region in the southeast China, soil degradation caused by soil erosion have greatly endangered agricultural development of this region. It is urgent to study and find a effective way to control soil erosion. Soil erosion is a complex process, rainfall and runoff supply energy for erosion, and soils act as object. Though many soil properties affecting soil erosion directly or indirectly, soil structure was thought as the most important one. Soil structure not only aversely affects soil by reducing infiltration rate, water-holding capacities, soil biota, and crop productivity, but also act as the foundation of soil quality assessment. To study the relationship between soil structure changes and soil erosion process, and soil structure stability mechanisms is helpful for the determination of soil erodibility factor and the prevention of soil erosion in this region. In this research, 10 soils derived from shale, Quaternary red clay and granite were studied. Soil structure stability and its mechanisms were studied by different methods, and the relationship between soil structure changes and erosion process were also studied by simulated rainfall experiment. The main results as followed:First, In the erosion process, erosion broke down soil structure and then the breakdown structure promoted the development of erosion, which couldn’t be separated. But, in the past researches, the two parts were often studied individually, and it was not suitable for us to understand the interaction between erosion and soil structure changes. In our study, the changes of soil structure and erosion process during rainfall were studied deeply, and their relationship were studied, which were help to promote the combination of soil erosion process and mechanisms.Our research studied the pore characteristic of three soils by using diagonal image. According the pore characteristics, the soil surface lay were divvied into three microlayers. And changes of the pore characteristics, such as pore size, pore shape with time and space were studied firstly, which were important to the quantitative analysis of the soil structure changes duiring rainfall.The ranking of the soil aggregate stability differed with different measurement method, soil aggregate size, stability parameters and breakdown mechanisms. In the wet-sieve method, based on parent materials, the aggregate stability of the soils were ranked in the order, granite> Quaternary red clay > shale. Based on erosion degree, the rank for the soils derived from granite was sight >medium>severe, While for the soils derived from Quaternary red clay, the rank was medium>severe>slight. Thefragment-size distribution (FSD) of soil aggregates differed with samples. More than 40% of the fraction of soils derived from granite(TGl,TG2) were at the size of >5mm and 5-2mm , and for the soil derived from shale(HS), more than 65% of the fractions were at the size of <0.25mm. The FSD of soils derived from Quaternary red clay were quite different themselves. The MWD of those six soils distributed from 0.41mm to 2.0mm, and the percent of >0.25mm ranged from 36% to 86%.Differed with parent material, the structure stability of the soils derived from granite were represented by coarse gravel, while the structure stability of the soils derived from shale and Quaternary red clay were represented by the stability of aggregates. The mechanisms of aggregate breakdown of the two latter were ranked in the order, slaking>mechanical breakdown>micro-cracking. The effect differed with soil and the initial size of aggregate. The small the aggregate was the higher the aggregate stability according NMWD.The aggregate stability of the soils were not related to SOM, pH, CEC, and the activity, of Fe(AL, Si)oxide, but were significant correlated to Fed, Ald, Alo, Sio and clay%. The results indicated that to the soils rich in sequioxide but poor in SOM, SOM could not play an important role on the stability of aggregate.Second, according the structure changes and the development of microlayers of soil surface, aggregate stability was important to maintain the structure. During the simulated rainfall, the surface structure of soils had a series of changes. For the soil derived from shale, at first, the unstable aggregate broken down in a large amount of finer particles, then the particles were compacted and formed a dense crust layers, and the density and the depth developed with time. The surface structure changes of soils derived from Quaternary red clay differed with soil aggregate stability. For the sample HQ1and HQ2 of which the stability were relatively unstable, aggregates were easier to be broke down and form soil crust than which of the samples HQ3 and HQ4, but the degree of soil crust development were far from which of soils derived from shale. The surface structures of HQ3 and HQ4 showed high stability. Which could not be observed obvious aggregate breakdown and crust formation. The soils derived from granite were very unstable, and crust could only be examined in TGI, and the fine particles of TG2 and TG3 loss seriously which caused the sandification significantly during erosion process.According to the microlayers development of soil surface, the soil surface divide into three layers: compacted layer or crust layer(Ll), transition Iayer(L2)and undisturbed layer(L3).Based on the percent of the pore area of the layer area (PA%) and the pore size, the ranking of the three layers were LKL2<L3.The pore size of LI was mainly in therange of <350 μ m, and which in L2 and L3 were >500 μ m. Usually, the shapes of smaller pore were round, while the larger size pores were irregular and elongate except HQ3. The pore characteristics also changed with time. The PA% of L1 of HS and HQ2 were declined with time, which declined from 2.25% and 3.72% to 0 and 0.37% in 30min. But the PA% of L2 didn’t declined obviously contrast to L1.During the erosion, the pore shapes also had some changes: the composite pore shapes of round, irregular and elongate turned to be round only in L1.Third, the erosion process was affected by raindrop kinetic energy and soil aggregate stability. Getting rid of raindrop kinetic energy by covering, the runoff yield and sediment yield reduced 5%~30% and 27%~76% respectively. The relationship between runoff yield and sediment yield were power function with covering, and the relationship between runoff yield and sediment yield were simple liner correlation with out covering . The sample TG3 had the highest sediment yield, and then HQ1and TG2, the sediment yields of the other four samples were lower relatively, the ranking of which were similar to the ranking of soil aggregate stability.The sediment from high-clay soils had more stability aggregates and less primary particles than high-sand and high-silt soils, therefore it was much coarser. The runoff electively transported 0.002-0.02mm particles, and contained 26.68%- 60.33% of this class particles in sediment. The transportability of thin-flow and its selection to sediment particles decrease when splash was eliminated. Fed, Ald, Alo and Sio decreased with the increase of sediments size of soils derived from granite. They were depleted in bigger particles and enriched in smaller particles. It made small particles more stable than the bigger ones. Fed, Ald and Alo increased with the increase of sediments size of soils derived from shale and Quaternary red clay. They were enriched in bigger particles make big particles stable.Soil aggregate stability was important to soil erosion. For the soils derived from shale and Quaternary red clay, most of the parameters of microaggregate and macroaggregate showed significant liner relationship with soil loss. And in the given condition of presetting the soils, the main mechanisms of aggregate breakdown and soil erosion were mechanical breakdown and transportation. The Fed, Ald, Alo, Sio and clay% affected soil erosion indirectly.更多还原