Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The Neossolos Litólicos and Regolíticos (Leptosols and Regosols) cover at least 15% of the Rio Grande do Sul state (RS) area. Those soils have been classified as low potential soils for general use, and also have been inadequately described in the field, due to difficulties in interpreting soil-saprolite-rock contacts. Besides, the classes of Neossolos, in the Brazilian Soil Classification System (SiBCS), are those needing improvements. The aim of this research was to analyze different profiles of Neossolos derived from volcanic rocks of the Serra Geral formation, disposed in a lito-climosequence in the RS. The research was separated into three investigation lines: a) chemical and mineralogical characterization of soil and saprolite profile; b)contributions to the morphologic analysis of Neossolos, including their saprolites; c) contributions to the taxonomic classification of Neossolo regolith. The results allowed verifying that the chemical and mineralogical characteristics and, consequently, the degree of weathering of the profiles are affected by the local climatic and geological conditions. Contacts of soil-saprolite, different from those found in the SiBCS, were identified in the field, through morphologic analysis. Thus, suggestions for the taxonomic classification of Neossolos derived from volcanic rocks in the RS were presented, seeking to contribute with the improvement of SiBCS. / Os Neossolos Litólicos e Regolíticos compreendem pelo menos 15% da área do Rio Grande do Sul (RS). Esses solos têm sido classificados como materiais de baixo potencial de uso geral, ao mesmo tempo em que têm sido inadequadamente descritos no campo, devido à dificuldade em se interpretar os contatos solosaprolito- rocha. Além disso, as classes dos Neossolos Litólicos e Neossolos Regolíticos, no Sistema Brasileiro de Classificação de Solos (SiBCS), são consideradas as que mais necessitam de aprimoramentos. Nesse sentido, o objetivo deste trabalho foi analisar diferentes perfis de Neossolos Litólicos e Regolíticos derivados de rochas vulcânicas da Formação Serra Geral, dispostos em uma litoclimoseqüência no RS. O trabalho foi dividido em três linhas de investigação: a) caracterização química e mineralógica de Neossolos e saprolitos; b) contribuições à análise morfológica de Neossolos e saprolitos; c) contribuições à classificação taxonômica de Neossolos e saprolitos. Os resultados permitiram verificar que as características químicas e mineralógicas e, conseqüentemente, o grau de intemperismo dos perfis são afetados pelas condições climáticas e geológicas locais. Foram encontrados, através de análise morfológica no campo, diferentes contatos solo-saprolito, os quais não apresentam correspondência no SiBCS. Nesse caso, propostas à classificação taxonômica de Neossolos derivados de rochas vulcânicas no RS foram sugeridas, visando contribuir para a evolução do SiBCS.

Aggregate stability and aggregate size distribution on soil surface that is impacted by rain drops affect soil erosion yet little is known about less weathered coarse textured soils. The objectives of the current study were to determine (i) the aggregate stability and associated aggregate fraction size distribution and (ii) the impact of the initial aggregate size on the aggregate stability and the resulting sediment fraction size distribution following rain drop impact in some quartz dominated coarse textured soils in the Eastern Cape Province. Soil samples for this experiment were collected from 14 ecotopes on the surface with a natural slope between 7.5 to 11% and at the depth between 0 to 0.2 m in the Eastern Cape Province. In each ecotope, twenty-five different spots were sampled using a spade at depth 0 to 0.2 m in other to eradicate biasness and ensure homogeneity. Thereafter, the soil samples were mixed to make a composite sample. The composited soil samples were then placed in rigid containers and taken to the soil science laboratory of the University of Fort Hare, Alice Campus where analyses were carried out. The soil properties were determined by passing the < 5 mm soil sample through a 2 mm sieve. The total Na, Ca and Mg contents in the soil samples were also determined using the wet digestion with sulphuric acid method. The total Soil organic matter content (SOM) was determined by the process known as weight loss on ignition. Thereafter, the fraction size distribution and aggregate stability was done by passing < 5 mm soil samples through a 3 mm sieve. The obtained calibrated aggregates between 3 and 5 mm were oven dried at 40o C. Thereafter, five gram (5g) of oven dried calibrated aggregates was immersed in a 50 mL deionized water in a 250 mL beaker for 10 minutes. The soil material left was transferred to a 0.053 mm sieve already immersed in ethanol and moved five times in the ethanol to separate < 0.053 mm from > 0.053 mm fragments. The remaining > 0.053 mm was re-immersed in ethanol and further oven dried at 40o C for 5 minutes. Thereafter, the > 0.053 mm fraction was transferred from 0.053 mm sieve, oven dried at 40o C, dry sieved using Digital Electromagnetic Shaker on a six column of sieves: 2 mm, 1 mm, 0.5 mm, 0.25 mm, 0.106 mm, and 0.053 mm. The aggregate stability was determined using the resulting size distribution in seven classes by calculating the mean weight diameter (MWD, mm). The soils were very stable, moderately stable or unstable. The presence of smectite and cultivation as opposed to pasture lowered aggregate stability. The studied soils showed three different aggregate size distributions. Unstable soils were dominated by 0.106 – 0.25 mm aggregate size and showed a positively skewed aggregate fraction size distribution. Aggregates finer than 0.106 mm were limited because of the coarse nature of the soil texture. Moderately stable soils broke down to both micro aggregates, 0.106 – 0.25 mm and macro aggregates, 2 – 5 mm giving a bimodal distribution. The aggregate size distribution in the very stable soils was dominated by the aggregate fraction size 2 – 5 mm and a negatively skewed aggregate fraction size distribution. The smaller the initial aggregate size the higher was the aggregate stability but the reverse was true for splash erosion. It was thought that the short 5 minutes duration of the rainfall might not have been enough to cause a total breakdown of the aggregates. Alternatively, ecotopes that were dominated by primary soil minerals such as quartz showed different breakdown behaviour compared to those containing secondary minerals such as kaolinite or smectite.

MSCAGR (Soil Science) / Department of Soil Science / The effects of tillage on soil structure and associated soil properties such as soil respiration may differ in different soils. The study determined the effects of tillage, soil texture and mineralogy in selected soil properties on different soil types. Soil samples were collected from four different sites in the Limpopo province, South Africa. The soils were classified as Glenrosa with sandy loam texture, Dundee with loamy sand, Hutton with clay, and Shortlands with clay. Glenrosa and Dundee were dominated by quartz, while Hutton and Shortlands with kaolinite. Soil samples were taken from the surface 0 – 20 cm under conventional tillage and no-till land. Soil organic matter, texture, and mineralogy were determined. The soils were wetted to activate the microorganisms and incubated for 70 days at 30℃ and soil respiration was determined using alkali trap method on a weekly basis. The study was conducted in triplicates and arranged in a completely randomized design. Data was subjected to analysis of variance using general linear model procedure of Minitab version 19. Means were compared using paired t-test at (p ≤ 0.05). The Pearson correlation coefficient (r) was used to measure the strength of linear dependence between variables. There was a significant difference in soil organic matter (p≤0.000) among all studied soils. The mean values of soil organic matter were 2.19% in Hutton, 2.0% in Shortlands, 0.54% in Glenrosa, and 0.43% in Dundee. Quartz had a strong negative linear relationship (r = -0.66) with soil organic matter while kaolinite had a strong positive linear relationship (r = 0.96). Soil respiration increased in soils dominated with quartz and decreased in soils dominated with kaolinite. The soil respiration increased by 18.95 g CO2 m-2 d-1 in conventional tillage and decreased by 13.88 g CO2 m-2 d-1 in no-tillage due to increased exposure of soil organic matter under conventional. It was concluded that less intensive tillage such as no-tillage reduces soil respiration. / NRF

Soft soil deposits of coastal regions and lowland areas pose many geotechnical problems but it is indispensable to utilize these grounds to meet the growing demand for infrastructure with ever increasing urbanization and industrial development. Soft soils are generally associated with high compressibility and low strength characteristics which augment the risk of huge settlements and foundation failure. It is essential to understand the complex behaviour of the ground consisting of soft clays as construction and maintenance of infrastructure in these areas is challenging. Marine sediments mostly possess open microstructure irrespective of the differences in their mineral composition and sedimentation environment. Also this particular microstructure in marine sediments is generally accompanied by the presence of a great amount of organic residues and fragments of marine organisms. Formation of pyrite is also possible because of the presence of decomposable organic matter, dissolved sulfate and reactive iron minerals. These soils due to their inherent mineralogy and microstructure have high void ratios and consequently high water holding capacity which explains the reason for their low shear strength and high compressibility characteristics. And often the formation environment is conducive for incorporation of organic content in the soft clay deposits which further aggravates the problem. A complete characterization of the soil can enhance the understanding of soil behavior and therefore can play a crucial role in suggesting suitable and sustainable ground improvement method. Soft clay deposits of Kuttanad area in Kerala, India extending to varying depths below the ground level, present a challenge as a foundation soil due to low bearing capacity and high settlement. Geologically Kuttanad is considered as a recent sedimentary formation. In the geological past, the entire area was a part of the Arabian Sea. Presently Kuttanad area covers an area of about 1,100 km2. Many intriguing reports of distresses to structures founded on this soil are available. An over view of specific characteristics of soft clays along with the comprehensive description of soft clays from various parts of the world is presented in the introductory Chapter. Deep soil mixing and mass stabilization methods are found to be relatively advantageous in reducing differential settlements and in achieving expeditious construction. A more detailed review of literature on Kuttanad soil problems and various ground improvement methods adopted are presented. The different ground improvement techniques attempted are soil reinforcement, stone columns, preloading etc. Soil mixing can be relatively advantageous over the other conventional ground improvement methods. Laboratory studies carried out earlier with different binders such as cement, lime and lime fly ash combinations did not exhibit appreciable improvement in soil strength. It is reasoned that the lack of understanding of the soil characteristics is responsible for the limited success of these attempts. Based on the review of literature the detailed scope of the work is presented at the end of Chapter 1. The method of collection of the soil from Kuttanad region, methods adopted for characterization of soil, characteristics of various binders used and testing procedures adopted for assessing the geotechnical behavior with and without binders are described in Chapter 2. In order to characterize the soil for understanding its behaviour under different conditions as well as to gauge its response to different stabilizers, a detailed physico¬chemical, mineralogical, morphological and fabric studies are carried out and presented in Chapter 3. An attempt has been made to explain the role of components of soils such as organic substances, pyrite and sesquioxides for variations in its properties with change in water content. The high water holding capacity of the soil reflected in its Liquid limit along with relatively low plasticity characteristics of the soil has been explained as due to the presence of minerals such as metahalloysite and gibbsite, the flocculated fabric, porous organic matter and water filled diatom frustules (amorphous silica). Based on the study conducted on the plasticity characteristics of Kuttanad soil under different conditions of drying and treatment, it was brought about that the organic content plays a dominant role in particle cementation and aggregation causing a substantial reduction in plasticity upon drying. Further, the presence of minerals such as pyrite and iron oxides also account for the plasticity changes. The significant changes in soil properties upon drying have also been successfully explained in Chapter 4. Attempts made to stabilize the soil using conventional chemical stabilizers are described in Chapter 5. The effect of binders on the strength improvement of soil has been explained based on the changes occurring in the composition, fabric and physico-chemical characteristics of soil upon addition of the binders. Lack of strength development in soil with lime has been attributed to the inherent composition of the soil hindering the formation of pozzolanic compounds and unfavourable modification of the fabric. On the other hand the soil responded well to cement stabilisation. The influence of various parameters such as Water/Cement (W/C) ratio, Initial water content, curing period and additive dosage on the strength development of cement treated soil has been examined. Cement improved the strength of the soil by binding the soil particles without depending on the interaction with the soil. It was observed that the role of initial water content is insignificant and the strength improved with reducing W/C ratio. The dependence of strength development with cement addition on the fabric at different W/C ratios has been assessed. Also the role of other additives such as Lime, Sand, Fly Ash, Ground granulated blast furnace slag, Silica fume and Sodium silicate to enhance the strength of cement treated soil has been analysed in Chapter 5. It was shown that only Sodium Silicate (NS) along with cement meets with good success. The studies on the undrained shear strength and compressibility characteristics of cemented soil carried out to understand the strength and deformation behaviour of the cemented soil are presented in Chapter 6. It is clear from the compressibility characteristics of the cemented soil that there is a well defined yield stress demarcating the least compressible pre-yield zone and more compressible post yield zone. Generally the yield stress increases with reducing water cement ratio. It is interesting to note that the post yield compressibility of the cemented soil is controlled more by the fabric of soil than by cementation effect. The study on the undrained shear behavior of cemented soil revealed that the cohesion intercept and angle of internal friction increases with addition of cement. However the impact of cementation is reflected more as increase in cohesion intercept with increasing cement content. The uniqueness of failure envelope observed for the cemented soil irrespective of whether the confining stress is above or below the yield stress has been explained in detail. A case study on the performance of embankment founded on Kuttand soil improved with Deep mixed cement columns (DMCC) has been evaluated through numerical simulations using FLAC 2D and this forms the subject matter of Chapter 7. For this work the soil properties of the Kuttanad soil determined by experimental investigations have been used. The simulation results showed that the introduction of DMCC columns improved the factor of safety against failure and reduced settlements. This study clearly endorses the analysis and the results of the test carried out on Kuttanad soil. The final chapter summarizes the details of the work carried out which brings out the importance of characterization of the soil in terms of soil components, physico-chemical environment as well as the micro structure of the soil in predicting the behaviour of the soil in changing environment and to understand the stabilization response of the soil with different binders which intern helps to select appropriate binder and or binder combinations.

PhDENV / Department of Ecology and Resource Management / Kaolin dominated soils are common in the tropical and subtropical regions. People depend on kaolin-rich soils for agricultural production of food and fiber. The most popular of all South African soils is the Hutton form which accounts for the marvelous redness of the landscape across the Country. The apedal (structureless) soils in the group are characterised by a relatively low CEC (< 11 cmolc kg-1) reflecting oxidic mineralogy with predominantly kaolinitic assemblage. The geochemical and mineralogical composition of soil kaolin has significant implications on soil fertility, geochemical exploration and engineering properties. Despite the dominance of kaolin in these soils, little is known of their properties in the medium. The nature of kaolin minerals in soils varies with parent material, degree of weathering and pedogenic environment. Most studies conducted in South Africa on kaolins are limited to reference kaolins with little or no publication on soil kaolins, hence, this study. This research involved the evaluation of mineralogical and geochemical characteristics of oxidic soils and soil kaolins developed from four (4) selected parent rocks which were basalt, granite, arkosic sandstone, and gneiss. Soils developed from quartzite were selected as control. Representative soil samples collected from profiles developed from the different parent rocks were analysed for physico-chemical, mineralogical, and geochemical data. The mineralogical and geochemical data obtained by x-ray diffractometry (XRD), x-ray fluorescence (XRF), and laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) were used in unraveling the influence of the provenance and degree of weathering on the soil characteristics. The mineralogical and geochemical data for soil kaolins were determined through XRD, scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis and differential scanning calorimetry, XRF, and LA-ICPMS to establish their mineralogical and geochemical properties with respect to their parent rocks. Comparison between the soil kaolins and selected reference kaolins were also conducted. The phosphorus (P) sorption data acquired photometrically were employed to evaluate the relationship between the P sorption capacities of the soils and soil kaolins. The influence of soil properties on the fertility of the soils were assessed based on the physico-chemical (pH, particle size distribution, and electrical conductivity (EC)) and chemical (organic matter (OM) content, cation exchange capacity (CEC), available P, exchangeable cations (Ca, K, Mg, Na, and Al), and P sorption) data. The mineralogical and geochemical data for the parent rocks were obtained by XRD, optical microscopy, XRF, and LA-ICPMS. Multivariate statistical analyses were also conducted. Results showed that the dominant colour in the studied bulk soils was dusky red (31 %) followed by brown (23 %), reddish brown, yellowish red, and yellowish brown (23 %) as well as strong brown, dark brown, reddish grey, very dark greyish brown, and dark red. Soil textures were clayey to sandy loamy with OM contents between 0.41 and 4.76 %. The pH, EC, CEC, exchangeable cations, and available P values generally ranged from 5.22 to 8.38, 10.25 to 114.40 μS/cm, 2.93 to 18.30 cmol/kg, 0.03 to 13.92 cmol/kg, and <0.01 to 54.99 mg/kg, respectively. Kaolinite and quartz were the dominant phases for soils developed from basalt whereas, quartz and plagioclase were the dominant mineral phases in soils developed from granite, arkosic sandstone, and gneiss, respectively. Other minerals present in the soils were microcline, muscovite, hematite, goethite, montmorrillonite, anatase, gibbsite, chlorite, and actinolite. Geochemical compositions of the bulk soils show relative enrichment of Fe2O3, TiO2, CaO, K2O, MgO, MnO, and Na2O (except for CaO, K2O, MgO, MnO, and Na2O in soils developed from basalt). Chemical index of alteration (CIA), chemical index of weathering (CIW), and plagioclase index of alteration (PIA) values varied between 54.92 and 99.81 % which suggest low to high degree of chemical weathering. The ACN-K and A-CNK-FM diagrams for the different soils also support these observations. Trace elements were generally enriched in soils developed from basalt and gneiss (except for Rb, Sr, and Ba in soils developed from basalt), but were depleted in soils developed from granite and arkosic sandstone (except for Cr and Ta). The principal factors responsible for the mineralogical and geochemical characteristics of the soils were the parent rocks and degree of weathering. In the soil kaolins, the dominant clay mineral was kaolinite accounting for 23 to 85 wt % followed by montmorrillonite, chlorite, and gibbsite. The non-clay minerals like quartz, plagioclase, muscovite, microcline, anatase, goethite, hematite, and actinolite accounted for the remaining percentages. The soil kaolins were characterised by thin platy kaolinite particles with partially to poorly-ordered structural order. The platy kaolinite crystals have their longest dimension sizes between 0.06 and 0.25 μm. The dehydroxylation temperatures for the studied soil kaolins ranged from 425 to 475 ˚C. The SiO2/Al2O3 ratio was lowest in soil kaolins developed from basalt and higher in soils developed from granite, arkosic sandstone, and gneiss which is consistent with their mineralogy since the former have more kaolinite. Higher Fe2O3 and CEC values were obtained relative to reference kaolins which could be attributed to the presence of more structural iron in the soil kaolins as well as their smaller crystal sizes. The presence of weatherable and accessory minerals accounted for the enrichment of Co, Ni, Cu, Zn, and Pb in the soil kaolins. The kaolinite in the soils were formed by leaching and desilication of the primary minerals in the parent rocks under suboxic conditions. H-type P adsorption isotherms obtained for both the soils and soil kaolins indicated their high affinity for phosphorus by chemisorption. The average maximum P adsorption values were in decreasing order of soils developed from basalt > granite > arkosic sandstone > quartzite (control) > gneiss, respectively whereas, for soil kaolins is basalt > granite > quartzite (control) > arkosic sandstone > gneiss, respectively. Relative to other soils developed from different parent rocks, soils developed from basalt (with more clay content) had higher capacity and buffer power for P adsorption. The standard P requirements for the soils ranged from 7.78 to 92.91 mgP/kg and were classified as low based on the Langmuir model. Significant correlation between the P adsorption parameters for the soils and soil kaolins indicated that the later could be taken as a good predictor for P sorption dynamics in the soils. Electrical conductivity of the soils were taken to be negligible in interfering with plant growth. The available P values were generally below the critical level of 12 – 15 mg/kg for soils developed from basalt, gneiss, and quartzite (control) but higher in soils developed from granite and arkosic sandstone. All the soil evaluation factor (SEF) average values estimated were greater than five indicating that they are not of poor soil fertility. The correlation results between the soil properties and P sorption parameters suggest that several variables can influence the P sorption dynamics of the soil. Regression analyses further indicated that CEC, pH, OM, and clay content in the soils account for 99 % bounding P energy variation whereas, Fe2O3 accounts for 76 % P sorption maximum variation in the soils. In addition, variations in Fe2O3 and sand contents in the soils account for 96 % and 95 % maximum buffering capacity and external P requirement (EPR) variations, respectively. Models to advance the interplay between the various soil properties and P sorption parameters in the soils were developed. Mineralogical and geochemical characteristics of the soils were principally controlled by the parent rocks and degree of weathering. The soil kaolins displayed significant differences relative to reference kaolins. Langmuir model is most suited for describing P sorption in soils and soil kaolins developed from different parent rocks within the studied area. P sorption parameters for the soils can readily be obtained from the P sorption parameters of the kaolins present in them. EPR obtained and models for predicting P sorption parameters from selected soil properties developed for the various soils will improve the efficiency of routine P fertilizer applications. Iron oxide (Fe2O3) played the most crucial role in explaining the P sorption dynamics of the soils. The major contributions from this study have been: better understanding of the influence of parent rock characteristics and degree of weathering on the soil characteristics, the nature of soil kaolins and its influence on soil properties as well as P sorption dynamics in soils have been better established, and improvement of the understanding on the relationship between soil properties and P sorption dynamics in the soils. / NRF