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1
Alvenäs, Gunnel. "Evaporation, soil moisture and soil temperature of bare and cropped soils /". Uppsala : Swedish Univ. of Agricultural Sciences (Sveriges lantbruksuniv.), 1999. http://epsilon.slu.se/avh/1999/91-576-5714-9.pdf.
Testo completo
2
Robert, Dilan Jeyachandran. "Soil-pipeline interaction in unsaturated soils". Thesis, University of Cambridge, 2010. https://www.repository.cam.ac.uk/handle/1810/265508.
Testo completoAbstract (sommario):
Pipelines that are used for the transport of energy and services are very important lifelines to modem society. Though pipelines are generally buried in unsaturated soils, the design guidelines are based on the assumption that the soil is either dry or fully saturated. For certain geotechnical problems, this assumption may not be acceptable because the water meniscus formed between soil particles creates an additional normal force between them by suction, which in turn forms temporary bonds. A recent series of large-scale physical model experiments at the Pipeline Engineering Research Laboratory (PERL) of Tokyo Gas, Japan show a higher peak load under unsaturated conditions compared to dry conditions. In contrast, recent experiments performed at Cornell University (CU) show that the soil-load due to lateral pipeline movement in dry and unsaturated sands are virtually the same. Thus, the effect of partial saturation on soil loading to pipeline may be different depending on soil type, moisture content and density. The current study investigates this problem through triaxial testing and constitutive modelling of the unsaturated soils used for the experiments and finite element simulations of the experiments. The mechanical behaviour of the sands used in the physical model experiments has been investigated by conducting a series of laboratory experiments. When compacted to the same energy level, Tokyo Gas sand exhibits larger strength in unsaturated conditions than in dry conditions at low confining stress levels mainly due to the suction-induced apparent cohesion generated by the fine particles present in the sand. In contrast, for coarser Cornell sand, the suction effect is found to be small even at low confining stress level, and hence the strength in unsaturated conditions is similar to that in dry ( or fully saturated) conditions. To capture the observed behaviour of dry as well as unsaturated soils, advanced constitutive soil models were developed. For dry (or fully saturated) soils, the modified Mohr-Coulomb and Original Nor-Sand (Cheong, 2006) models were able to simulate the general behaviour including the strain softening effect. To cater for the behaviour of unsaturated soils, the saturated versions of the NorSand and the modified Mohr-Coulomb models were modified in conjunction with the generalised effective stress framework. By simulating the triaxial experimental data, it is demonstrated that the developed models can predict the realistic soil behaviour of unsaturated soils. Using the developed models, the large scale physical model experiments of pipelines subjected to lateral soil movements at PERL and CU were simulated by the explicit finite element method. Good agreement was found between the numerical models and the experiments. Further FE analyses were conducted to investigate the pipeline behaviour under lateral soil movement at conditions of different HID's, moisture contents, and relative densities. The results were synthesized to produce new normalised pipe load charts. Three dimensional finite element analysis was performed to simulate the soil-pipeline interaction under strike-slip fault movements. The finite element model was first validated by comparing the computed results to the data produced from a full scale experiment carried out at CU. The analysis was then further extended by varying the initial conditions of the sand (sand type, density, moisture content, etc.), pipe material, pipe burial depth, and pipeline-fault rupture inclination. It was found in all cases that the peak lateral loads on the pipelines subjected to strike-slip fault movements are less than or equal to the peak loads computed by the 2-D lateral movement simulations.
3
Ekanayake, Jagath C. "Soil water movement through swelling soils". Lincoln University, 1990. http://hdl.handle.net/10182/1761.
Testo completoAbstract (sommario):
The present work is a contribution to description and understanding of the distribution and movement of water in swelling soils. In order to investigate the moisture distribution in swelling soils a detailed knowledge of volume change properties, flow characteristics and total potential of water in the soil is essential. Therefore, a possible volume change mechanism is first described by dividing the swelling soils into four categories and volume change of a swelling soil is measured under different overburden pressures. The measured and calculated (from volume change data) overburden potential components are used to check the validity of the derivation of a load factor, ∝. Moisture diffusivity in swelling soil under different overburden pressures is measured using Gardner's (1956) outflow method. Behaviour of equilibrium moisture profiles in swelling soils is theoretically explained, solving the differential equation by considering the physical variation of individual soil properties with moisture content and overburden pressure. Using the measured volume change data and moisture potentials under various overburden pressures, the behaviour of possible moisture profiles are described at equilibrium and under steady vertical flows in swelling soils. It is shown that high overburden pressures lead to soil water behaviour quite different from any previously reported.
4
Zhang, Guanghui, e 張廣輝. "Soil-water characteristics of sandy soil and soil cement with and without vegetation". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2014. http://hdl.handle.net/10722/208025.
Testo completoAbstract (sommario):
The use of soil cement as a growth medium was examined in this study. During the monitoring, green soil cement revealed diverse ecological values. The survival rates of plants in each soil conditions were higher than 80%,which was very promising. Furthermore, the survival rates dropped when the soil density reached95%, which means soil density might influence the survival rate of plant. Plant growth rates in sandy soil were higher than that in soil cement. In particular, low soil density facilitated plant growth in sandy soil, whereas density effect was not clear to plant growth performance in soil cement.
Experiments were undertaken to study the soil-water characteristics of sandy soil and soil cement in field and laboratory condition. The influence of vegetation and material density on the development of negative pore water pressure (PWP) and degree of saturation (Sr) in the studied materials was investigated. The field planting experiments proved a promising survival rate of Schefflera heptaphylla in both types of materials while sandy soil promoted better growth of the seedlings than the soil cement. From the field study, PWP and Sr of sandy soil responded noticeably and promptly to natural drying and wetting cycles. However, the responses in soil cement were relatively mild. When subjected to the same drying-wetting cycles, PWP responded more slowly and to a smaller magnitude compared with that of soil cement. In addition, Sr changed little in soil cement. An increase in the density of the sandy soil promoted rapid development of negative PWP, while an opposite trend was observed for soil cement. Attempts have been made to explain the observations from the perspectives of material permeability and change in water content during a drying period in both soil types. Furthermore, in sandy soil, the development of PWP (with a measurement limit of -90 kPa) was minimally affected by the presence of vegetation, while vegetation noticeably helped the development of negative PWP in the soil cement. Bounds of the soil-water characteristic curve of the studied materials were presented based on estimates from the drying and wetting scanning curves derived from the field monitoring. A complementary laboratory study was carried out in an environmental chamber with controllable temperature and humidity. Monitoring results from the laboratory agreed well with that obtained from the field.published_or_final_version
Civil Engineering
Master
Master of Philosophy
5
Corneo, Paola Elisa. "Understanding soil microbial community dynamics in vineyard soils: soil structure, climate and plant effects". Doctoral thesis, country:CH, 2013. http://hdl.handle.net/10449/23970.
Testo completoAbstract (sommario):
This thesis aimed at characterising the structure of the bacterial and fungal community living in vineyard soils, identifying and describing the parameters that explain the distribution of the
microbial communities in this environment.
Vineyards represent an economical relevant agro-ecosystem, where vines, long-lived woody-perennial plants, are normally cultivated at different altitudes. The maintenance of the soil quality is at the base of a productive agriculture and thus the investigation of its biological
component, its structure and all the processes that take place into the soil are of importance. Microorganisms represent one of the main biological components of the soil and they are involved in numerous bio-geochemical processes, such as nutrient cycling and degradation of the soil organic matter (SOM). The understanding of the effect of abiotic and biotic factors on the
soil microbial communities is crucial for the maintenance of this agro-ecosystem.
Considering that viticulture is widespread in North Italy we selected the Trentino region as study area at the basis of our investigations. A first on field study was carried out on soils collected in nine vineyards located along three altitudinal transects. The sites were selected on the basis of the same soil origin, texture and pH, and similar weather conditions. Our aim was to understand the effect of altitude considered as a climatic and physicochemical gradient on the soil bacterial and fungal community, comparing the soil microbial structure at different altitudes (200, 450, 700 m a.s.l.) and in different seasons. Along these altitudinal gradients, soil temperature is decreasing while soil moisture is increasing, thus offering an experimental design to investigate the effect of these climatic parameters. To further exploit the effect of soil temperature, we then carried out one year microcosm experiment. Temperature is one of the main factors affecting soil microbial communities and the recent worries about climate change stimulated the interest in a better understanding of its effect. Our aim was to assess the effect of temperature alone, isolating its effect from all the other parameters present in the field. In particular we investigated the effect of soil seasonal temperature fluctuations and the effect of a moderate soil warming of 2 °C above normal seasonal temperatures. Furthermore we assessed the effect of stable temperatures without fluctuations (3 and 20°C). To fully characterise the vineyard environment we conducted a third experiment to understand the effect of weeds and of soil type on the bacterial and fungal community structure, to reflect on their role in this environment. Weeds are widespread plants in the vineyards and are usually controlled because they compete for nutrients with vines. Through a greenhouse experiment where we used a combination of three different weeds (Taraxacum officinalis, Trifolium repens and Poa trivialis) and four different soils collected in vineyard, we aimed at characterising the bacterial and fungal communities of the bulk and rhizosphere soil and of the roots. The genetic structure of the soil bacterial and fungal communities in the three different experiments was assessed by automated ribosomal intergenic spacer analysis (ARISA), a fingerprinting technique based on the analysis of the length heterogeneity of the bacterial and fungal internal transcribed spacer (ITS) fragment. Multivariate analyses were carried out to
visualise and determine the effect of the different parameters investigated on the soil microbial community ordination. We found that altitude, behaving as a physicochemical gradient separates the soil microbial community living at 200 and 700 m a.s.l. Different parameters correlating with altitude explained the distribution of bacteria and fungi in the altitudinal transects. Qualitatively the different
vineyards were characterised by a stable core microbiome, a number of ribotypes stable in time and space. Among the climatic parameters, while soil moisture was correlating with altitude and helped explaining the distribution of the microbial communities, the soil temperature did not play any role. Seasonally the soil microbial communities were stable and the differences among the soil microbial communities living at the lower and higher sites were related to the physicochemical parameters and not to the temperature effect. Investigating the effect of temperature in microcosm experiment, isolating its effect from all the other parameters, we determined the presence of a direct effect of temperature, soil type dependent. The soil bacterial
community was fluctuating under the effect of temperature fluctuations, while the fungal community was mainly stable. Soil warming did not have any effect on the microbial community as observed on field in the altitudinal gradient, where temperature was not the factor explaining the differences between the microbial community at 200 and 700 m a.s.l. Vineyards, as other
temperate environments, are quite stable to subtle changes in soil temperatures in the range forecasted by the climate change events. Even if we did not find a direct effect of temperature on the soil microbial communities, temperature could indirectly affect the soil microorganisms, acting on plant cover, nutrients availability, soil moisture and plant exudation. The soil structure was the main determinant of the microbial community associated to the bulk
soil also in presence of plants. Characterising the microbial community associated to the weeds, we found that the different compartments (roots, rhizosphere and bulk soil) were colonised by
qualitatively and quantitative different microbial structure, in particular on the roots. Differences in the microbial community associated to the rhizosphere and to the bulk soil were plant type dependent. The structure of the microbial community associated to the roots was mainly
determined by the plant species, while the soil type was the main determinant of the microbial community associated to the bulk soil. Weeds are not expected to particularly affect the bacterial community associated to the bulk soil in vineyards, while they could play a role shaping the soil fungal community
6
Njie, Momodou. "Modelling soil moisture dynamics in vegetated soils". Thesis, Imperial College London, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.406159.
Testo completo
7
Dash, Suresh R. "Lateral pile soil interaction in liquefiable soils". Thesis, University of Oxford, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.543468.
Testo completo
8
Gebhardt, Martha Mary. "Soil Amendment Effects on Degraded Soils and Consequences for Plant Growth and Soil Microbial Communities". Thesis, The University of Arizona, 2015. http://hdl.handle.net/10150/556614.
Testo completoAbstract (sommario):
Human activities that disrupt soil properties are fundamentally changing ecosystems. Soil degradation decreases microbial abundance and activity, leading to changes in nutrient availability, soil organic matter, and plant growth and establishment. Land use and land cover change are widespread and increasing in semiarid regions of the southwestern US, which results in reductions of native plant and microbial abundance and community diversity. Here we studied the effects of soil degradation and amendments (biochar and woodchips) on microbial activity, soil carbon and nitrogen availability, and plant growth of ten semi-arid plants species native to the southwestern US. Results show that woodchip amendments result in poor overall plant growth, while biochar amended soils promoted plant growth when soil quality was reduced. Additionally, amendments had a strong influence on microbial activity, while the presence and species identity of plants did not. Biochar amended soils led to increases in the potential activities of enzymes involved in the degradation of carbon, nitrogen, and phosphorus rich substrates. Woodchips, caused an increase of potential activity in enzymes involved in the degradation of sugar and proteins. These results show that microbes and plants respond differently to soil treatments and suggest that microbial responses may function as earlier indicators of the success of re-vegetation attempts.
9
Wagai, Rota. "Climatic and Lithogenic Controls on Soil Organic Matter-Mineral Associations". Fogler Library, University of Maine, 2005. http://www.library.umaine.edu/theses/pdf/WagaiR2005.pdf.
Testo completo
10
Keller, Thomas. "Soil compaction and soil tillage - studies in agricultural soil mechanics /". Uppsala : Dept. of Soil Sciences, Swedish Univ. of Agricultural Sciences, 2004. http://epsilon.slu.se/a489.pdf.
Testo completo
11
Coyle, Kieran. "An investigation of the role of soil micro-organisms in phosphorus mobilisation : a report submitted to fulfil the requrements of the degree of Doctor of Philosophy". Title page, table of contents and abstract only, 2001. http://web4.library.adelaide.edu.au/theses/09PH/09phc8814.pdf.
Testo completo
12
TOUFIGH, MOHAMMAD MOHSEN. "BEHAVIOR OF UNSATURATED SOIL AND ITS INFLUENCE ON SOIL - SOIL INTERACTION AT AN INTERFACE". Diss., The University of Arizona, 1987. http://hdl.handle.net/10150/184224.
Testo completoAbstract (sommario):
The interface failure between caps and natural soil in trenches containing buried low level nuclear waste material was investigated in this study. The Casa Grande Highway Farm (CGHF) soil was used for the entire investigation. This soil is described as being a silty sand with approximately 23% by weight passing sieve No. 200. Other preliminary testing was performed on the same soil. Isotropically consolidated drained (CID) tests were performed on the laboratory compacted samples at different degree of saturation including fully saturated specimens. Suction pressure was measured in the laboratory by adopting pressure plate extractor and compared with determined effective suction in triaxial testing. A generalized failure equation, in term of strength parameters and suction pressure, was defined for all degrees of saturation. The consideration of unsaturated soil sets the current modified model apart from previous bounding surface which only allows use of fully saturated cohesive soil. The saturated material constants associated with the model are identified. These new constants are obtained from a generalized failure equation. The model was then verified by comparing predictions with other laboratory tests which are not used in the calibration. Generally a good agreement between the model and test results was found for stress-strain, stress path and volumetric strain response at different degrees of saturation. Extensive interface tests were performed in the conventional direct shear machine with some modification. Similar to trench cap soil and natural soil in the field, the test specimens were prepared at different degrees of saturation and density (compaction effort). Comparisons were made for the effects of magnitude of normal load, degree of saturation, density, compaction effort, moisture migration and dissimilar bodies density. An interface element and the modified bounding surface model and elasticity model was used in a finite element program to predict the interface response for the laboratory results and actual field problems. Material parameters related to the interface were identified and good predictions were observed for the interface behavior.
13
Li, Xu. "Dual-porosity structure and bimodal hydraulic property functions for unsaturated coarse granular soils /". View abstract or full-text, 2009. http://library.ust.hk/cgi/db/thesis.pl?CIVL%202009%20LI.
Testo completo
14
Pengthamkeerati, Patthra. "Soil physical and microbiological properties affected by soil compaction, organic amendments and cropping in a claypan soil /". free to MU campus, to others for purchase, 2004. http://wwwlib.umi.com/cr/mo/fullcit?p3164537.
Testo completo
15
Gusli, Sikstus. "Effect of methods of wetting and rainfall characteristics on crusting and hardsetting of a red-brown earth". Title page, abstract and table of contents only, 1995. http://web4.library.adelaide.edu.au/theses/09PH/09phg982.pdf.
Testo completoAbstract (sommario):
Includes bibliographical references. The beneficial effects of tillage are often negated in Australian soils by poor aggregate structural stability. If irrigation or rain falls on exposed freshly tilled soil, crusting or harsetting often develops on drying. Rainfall intensity, kinetic energy, rate of wetting, antecedent water content and soil management history have been implicated in aggregate breakdown.
16
Twomlow, Stephen John. "Soil loosening and drainage efficiency of silt soils". Thesis, University of Plymouth, 1989. http://hdl.handle.net/10026.1/2738.
Testo completoAbstract (sommario):
An experiment was set up to investigate the effects of soil loosening on the drainage efficiency of a structurally unstable silty clay loam in Devon. Such soils are common to the Palaeozoic slates of South West England, and in many parts of Wales and Scotland. The dominance of the fine earth fraction these soils by silt sized particles and the associated low clay fractions ( 10-35%) gives rise to weak structures that are unsuitable f or mole drainage. Six drains were laid with permeable fill at a 20 m spacing on a gently sloping site at Seale-Hayne College Farm. A year after installation half the site was loosened to a depth of 0.4 m. The whole site was then cultivated and winter wheat sown. The study concentrated on the modification of the soil physical environment and water transmission routes following loosening operations for autumn re-wetting, the winter period and spring drying. Data collection involved the analysis of drainflow hydrographs and the measurement of soil water physical parameters. Results from an intensive twelve month monitoring period indicate that the modification of subsoil to improve drainage does not necessarily give the results expected . In this study it has been shown that loosening of an unstable silty clay loam did not enhance drainage, in fact the reverse was true which can have dire consequences in terms of trafficability and plant root growth. Loosening lead to an increased porosity which resulted in a greater, albeit temporary, retention of water within the disturbed zone. This means that loosened soils were wetter prior to a rainstorm and remained so for a longer period after rainfall. This response, in turn lead to significant reductions in soil shear strength, which has important implications for successful crop husbandry in the autumn and spring periods when field operations are necessary. Further work is required to assess the temporal persistence of soil loosening on soil physical conditions and crop responses.
17
Stinghen, Geovanne Silva. "Assessment of nitrogen efficiency in maize due to soil compaction and changes in soil physical properties /". free to MU campus, to others for purchase, 2004. http://wwwlib.umi.com/cr/mo/fullcit?p1422967.
Testo completo
18
Brandsma, Richard Theodorus. "Soil conditioner effects on soil erosion, soil structure and crop performance". Thesis, University of Wolverhampton, 1997. http://hdl.handle.net/2436/99094.
Testo completo
19
Grieger, Gayle. "The effect of mineralogy and exchangeable magnesium on the dispersive behaviour of weakly sodic soils /". Title page, table of contents and abstract only, 1999. http://web4.library.adelaide.edu.au/theses/09PH/09phg8478.pdf.
Testo completo
20
Yeow, Hoe Chian. "Soil classification through dynamic soil signatures". Thesis, University of Aberdeen, 1990. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU031990.
Testo completoAbstract (sommario):
The demand for a cost effective site investigation method has resulted in the introduction of various advanced in-situ testing techniques. These techniques utilise modern electronics instrumentation to monitor various soil parameters during site investigation. The data is then processed using high speed, low cost digital computers which allow an accurate and rapid assessment of the conditions of the foundation soil under a proposed construction site. In this thesis, a site investigation tool that drives a coring tube into the ground under a combination of vibration and impact is considered. This machine, called a vibro-impact corer, is fully instrumented to provide penetrometer-type information and a core sample for further inspection in the laboratory. The self-adjusting mechanism inherent in this machine delivers the minimum level of energy required to overcome soil resistance which thereby allows continuous penetration of the coring tube. This mechanism is also results in minimal induced disturbance during the coring process. This thesis investigates use of the vibro-impact corer as a soil classification tool. It involves the design of data analysis software to perform the soil classification procedure. Due to the nature of the system, the resistance monitored through the annular load cell fitted at the tip of the coring tube consists of the dynamic end resistance waveform and the peak magnitude of these waveforms over a sampling period. The vibro-impact soil classification system is based on the distinct self-adjusting mechanism of the machine. The self-adjustment mechanism imparts a different level of impact and vibration as soil conditions change which produces distinct dynamic soil resistance waveforms. In addition, the penetration rate and the magnitude of the soil resistance encountered also varies according to the material being penetrated. These two features are used to form the basis of the soil classification system in this software. The software also includes options for empirical correlation of the results obtained from the vibro-impact penetrometer with the CPT and SPT tests to allow comparison. The vibro-impact soil classification software is designed to be user-friendly. It reads the data files from a Biodata Transient Capture System for the classification process. The output devices such as plotter and printer are used to produce hardcopy records for various data. All the options are menu driven. A two degree freedom simulation of the operational responses of the vibro-impact machine is also included in this thesis. The main objective of this simulation is to study the soil response during vibro-impact mode of driving. This allows a comparison of the simulation soil responses to the model test results to provide an understanding of the soil behaviour under a combination of both vibratory and impact loadings. This thesis presents the results of several laboratory model and full scale vibro-impact penetrometer tests. It concentrates on the main subject of soil classification during the discussions although in some occasions the operational mechanism of the machine is mentioned. The results justify the approaches adopted for the soil classification system using a vibro-impact machine.
21
Dove, Jonathan Thomas Barnett Mark O. "Mercury immobilization by subsurface reactive barriers". Auburn, Ala, 2009. http://hdl.handle.net/10415/1901.
Testo completo
22
Wearing, Cameron. "Sodicity and soil microstructure /". [St. Lucia, Qld.], 2005. http://www.library.uq.edu.au/pdfserve.php?image=thesisabs/absthe18523.pdf.
Testo completo
23
Saez, Carolin Cordova. "Spatial variability of soil organic matter fractions in arable and grassland soils - implications for soil N supply". Thesis, University of Reading, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.542058.
Testo completo
24
Miller, Christopher James. "Mechanisms of water colour release from organic soils and consequences for catchment management". Thesis, Available from the University of Aberdeen Library and Historic Collections Digital Resources. Online version available for university members only. This requires an institutional login off-campus, 2008. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?application=DIGITOOL-3&owner=resourcediscovery&custom_att_2=simple_viewer&pid=24724.
Testo completo
25
Limprasert, Tawan. "Behavior of soil, soil-cement, and soil-cement-fiber under multiaxial test". Ohio : Ohio University, 1995. http://www.ohiolink.edu/etd/view.cgi?ohiou1179260769.
Testo completo
26
Limprasert, Tawan. "Behaviour of soil, soil-cement and soil-cement-fiber under multiaxial test". Ohio University / OhioLINK, 1995. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1179260769.
Testo completo
27
Duval, Jean. "Assessing porosity characteristics as indicators of compaction in a clay soil". Thesis, McGill University, 1990. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=59275.
Testo completoAbstract (sommario):
Persistent soil compaction by heavy-axle-load vehicles is a growing concern for the long-term productivity of clay soils. For optimum soil management, however, we must be able to evaluate adequately soil structural damages. This study compares different methods of assessing soil structure as affected by compaction and subsoiling treatments in a clay soil under corn production.The tests used were: total porosity as calculated from densimeter readings and from soil cores; structural porosity; water desorption characteristics; and soil profile examination. These tests were performed in three layers of 20 cm and evaluation was based on their practicality and their ability to differentiate between treatments and to correlate with corn yield.
The results confirm that total porosity is a poor indicator of compaction in the subsoil. In soil profile assessments, ped descriptions were preferable to examination of pores. Water content and saturation deficit at $-$4.0 and $-$100 kPa were the best indicators of treatments and plant response.
28
Hoyle, Frances Carmen. "The effect of soluble organic carbon substrates, and environmental modulators on soil microbial function and diversity /". Connect to this title, 2006. http://theses.library.uwa.edu.au/adt-WU2007.0050.
Testo completo
29
Sandhu, Harjinder. "Sorption of lead and arsenic on soil components and effectiveness of phosphates for remediating lead and arsenic contaminated soils". Morgantown, W. Va. : [West Virginia University Libraries], 2001. http://etd.wvu.edu/templates/showETD.cfm?recnum=1923.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--West Virginia University, 2001.Title from document title page. Document formatted into pages; contains xii, 170 p. : ill. (some col.). Includes abstract. Includes bibliographical references.
30
Jenkins, Anthony Blaine. "Organic carbon and fertility of forest soils on the Allegheny Plateau of West Virginia". Morgantown, W. Va. : [West Virginia University Libraries], 2002. http://etd.wvu.edu/templates/showETD.cfm?recnum=2486.
Testo completoAbstract (sommario):
Thesis (M.S.)--West Virginia University, 2002.Title from document title page. Document formatted into pages; contains x, 282 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references.
31
Barzegar, Abdolrahman. "Structural stability and mechanical strength of salt-affected soils". Title page, contents and abstract only, 1995. http://web4.library.adelaide.edu.au/theses/09PH/09phb296.pdf.
Testo completoAbstract (sommario):
Copies of author's previously published articles in pocket inside back cover. Bibliography: leaves 147-160. This thesis outlines the factors affecting soil strength and structural stability and their interrelationship in salt-affected soils. The objectives of this study are to investigate the influence of clay particles on soil densification and mellowing, the mellowing of compacted soils and soil aggregates as influenced by solution composition, the disaggregation of soils subjected to different sodicities and salinities and its relationship to soil strength and dispersible clay and the effect of organic matter and clay type on aggregation of salt-affected soils.
32
Renforth, Phil. "Mineral carbonation in soils : engineering the soil carbon sink". Thesis, University of Newcastle Upon Tyne, 2011. http://hdl.handle.net/10443/1216.
Testo completoAbstract (sommario):
Rapid anthropogenic climate change is one of the greatest challenges that human civilisation will face in the 21st century. A 25-180 % increase in atmospheric carbon dioxide content since the early 1800’s and a predicted increase of 2-3% each year will lead to a 2-6°C rise in tropospheric temperatures. The consequences of increased atmospheric temperatures are profound and would put unsustainable strain on human infrastructure, which was conservatively estimated in the Stern Review (2006) to cost approximately 20% of GDP. Given the political, technical, economic and social barriers preventing the transition to a low carbon economy, there is an unequivocal need to research ‘geoengineering’ technologies that can bridge the gap between carbon emission reduction targets and actual emissions. Soil mineral carbonation is one such technology. The atmosphere is one of the smallest carbon pools at the Earth’s Surface (depending on how each pool is demarcated). Soils turn over the quantity of carbon in the atmosphere in under a decade and collectively form one of the largest carbon pools (3-4 times the quantity of carbon in the atmosphere). Land use change since the agricultural revolution has released 256 GtC (40 % of anthropogenic emissions). Research investigating the potential for carbon accumulation in soils is primarily focused on restoring organic carbon concentration to pre-agricultural values through modification of farming practices. The research presented in this thesis is the first that explores the potential of increasing the inorganic carbon pool as an emissions mitigation technology. Inorganic carbon accumulation is promoted by introducing divalent cation rich (predominantly calcium and magnesium) silicate and hydroxide minerals into the soil, which weather and supersaturate the soil solution with respect to carbonate minerals (predominantly calcite, aragonite, magnesite and dolomite). The carbon in the resultant precipitate is derived from the atmosphere. This is analogous to mineral carbonation technologies which induce carbonate precipitation from silicate weathering in industrial scale reactors at elevated temperatures and pressures. However, carbonation in soil exploits natural weathering processes to the same effect with minimal energy and infrastructure input. The research presented in this thesis broadly investigates soil mineral carbonation by contributing work towards the fundamental issues associated with application of soil mineral carbonation technology. Research activity described herein covers a range of laboratory batch weathering experiments, field work, geochemical modelling, plant growth trials, soil microcosm experiments and literature reviews. While eclectic, all work packages contribute to the same goal of describing the efficacy, effectiveness and potential impacts of soil mineral carbonation. The efficacy of mineral carbonation technology is primarily limited by the availability of appropriate silicate bearing material. A literature search suggests that approximately 15-16 Gt a- 1 of silicate rich ‘waste’ materials are produced as a consequence of human activity. This has a carbon capture potential between 190 and 332 MtC a-1, which is equivalent to other emissions mitigation strategies. Quarrying silicate specifically for carbonation is a suggested strategy that may be able to store on the order of 102 GtC a-1 (based on two sites in the US). Therefore, mineral carbonation may form part of global mitigation strategies collectively equivalent to 14 GtC a-1 to stabilise the CO2 concentration of the atmosphere at 500 parts per million by volume. Considering that the potential capacity of soil mineral carbonation is sufficient to act as a substantial emissions mitigation strategy it was appropriate to investigate issues associated with the application of such a technology. In the first instance, sites known to contain silicates were investigated. These include soils developed on natural silicates (on the Whin Sill in Northumberland), construction and demolition waste (at a brownfield site and waste transfer stations) and slag (at a former steelworks). Interpretation of fieldwork results suggests that inorganic carbon accumulation is rapid (up to 38 gC kg-1(soil) a-1), and is orders of magnitude xxv greater than organic carbon accumulation in natural soils. The average concentration of inorganic carbon (20-30 Kg m-3) is equivalent to organic carbon in natural soils. The unusually light carbon and oxygen isotope ratios of the carbonate (-3.1 ‰ and -27.5 ‰ for δ13C and -3.9 ‰ and -20.9 ‰ for δ18O) were used to determine that up to 55% of the carbon was derived from the atmosphere. The rate of carbon capture, which is the same as the precipitation rate of carbonate, is a function of solution chemistry. The more supersaturated a solution is with respect to a carbonate mineral, the more rapid the precipitation rate. Saturation of a solution is a function of divalent cation and carbonate anion concentration. Therefore, the supply of each of these components was investigated in laboratory experiments. Batch weathering experiments were used to investigate the supply of calcium from artificial silicates (hydrated cement gel). Up to 70-80 % of the calcium contained in the mineral was removed, which is consistent with efficiencies reported for conventional mineral carbonation. The log rate of weathering was between -10.66 and -6.86 mol Ca cm-2 sec-1, which is several orders of magnitude greater than that usually reported for natural silicates. Microcosm experiments were conducted to investigate the rate of supply of carbonate from the organic carbon mineralisation in high pH solutions. The research clearly demonstrates that high pH solutions inhibit the breakdown of organic carbon as a function of nutrient supply. Where organic carbon was successfully mineralised the log rates (-3.4 mmol g-1(field moist soil) sec-1) were equivalent to that found in previous studies. While the influx of dissolved carbonate mineral components into the soil solution is the primary controlling step in the rate of carbon accumulation, there is a complex relationship between soil physical properties and geochemistry. This was highlighted in a numerical model that was constructed for this thesis, which suggests that soil pore volume and particle size distribution are important variables. An additional numerical model was constructed to investigate the transportation of silicate material to the application site. This model suggests that an economics of soil mineral carbonation is a function of transport costs, the value of the silicate material and the price of carbon. Field observations, growth trials, microcosm experiments and previous research suggest a complex interaction between biology, weathering and carbonate precipitation. Additional work is required to investigate carbonate precipitation mediated by plant and microorganism activity and the degree to which soil mixed with silicates impact on ecosystem functioning. This research has demonstrated that mineral carbonation in soils could form a substantial emissions mitigation strategy, but additional work is required in a number of areas to which this thesis provides a suitable foundation.
33
Wallace, Eileen P. "Soil classification and radionuclide migration in west Cumbrian soils". Thesis, University of Newcastle Upon Tyne, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.327266.
Testo completo
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Riggs, Katherine Sarah. "Soil chemical changes following limestone additions to acid soils". Thesis, University of Newcastle Upon Tyne, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.315889.
Testo completo
35
McDonald, Noeleen Theresa. "Soil tests for predicting nitrogen supply in Irish soils". Thesis, Queen's University Belfast, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.675659.
Testo completoAbstract (sommario):
Existing nitrogen (N) fertilizer recommendations for Irish grassland do not account for the potential variability in soil N supply through N mineralization. Research carried out within this thesis aims to identify a suitable N test that can estimate the potential range of N supplied in temperate soils and to increase the knowledge of soil metabolites linked with soil N mineralization. To fulfill these aims a series of interlinking studies were conducted. Initially laboratory studies investigating various soil N pools and N tests were undertaken, then a more in depth analysis of the carbon (C) and N metabolites in these soils was conducted using proton nuclear magnetic resonance spectroscopy (1H NMR). Following this a microcosm study was conducted to validate the laboratory findings and finally, field studies to investigate the temporal variability of soil N pools and their relationship with grass production. The laboratory studies found that there was large differences in mineralizable N (MN) capacity between Irish grassland soil types and that the Illinois soil N test (ISNT-N) was the best rapid predictor of MN across these soil types. The 1 H NMR analysis of these soils identified 7 metabolites, most as labile sources of C linked as regulators of N mineralization. The microcosm experiment, showed that a model combining ISNT-N, total oxidized N (TON), C:N and the interaction of ISNT-N X C:N best predicted grass OM production and N uptake. In the field study, soil mineral N was found to be highly transient, over the 15 month sampling period, while MN was less variable. Daily grass OM production was mainly explained by climatic variables and further evaluation across multiple seasons is therefore warranted. Overall this study highlights the real opportunity to improve N use efficiency with soil N testing, hence reducing costs to the farmer and losses to the environment.
36
Tenywa, Moses Makooma. "Soil erosion overland flow processes on spatially variable soils /". The Ohio State University, 1993. http://rave.ohiolink.edu/etdc/view?acc_num=osu148784853136528.
Testo completo
37
Silvertooth, J. C., A. Galadima e E. R. Norton. "Residual Soil Nitrogen Evaluations in Irrigated Desert Soils, 2001". College of Agriculture, University of Arizona (Tucson, AZ), 2002. http://hdl.handle.net/10150/197713.
Testo completoAbstract (sommario):
Field experiments were conducted in Arizona in 2001 at three locations (Maricopa, Marana, and Safford). The Maricopa and Safford experiments have been conducted for14 consecutive seasons and the Marana site was initiated in 1994. The original purposes of the experiments were to test nitrogen (N) fertilization strategies and to validate and refine N fertilization recommendations for Upland (Gossypium hirsutum L.) and American Pima (G. barbadense L.) cotton. The experiments have each utilized N management tools such as pre-season soil tests for NO₃⁻-N, in-season plant tissue testing (petioles) for N fertility status, and crop monitoring to ascertain crop fruiting patterns and crop N needs. At each location, treatments varied from a conservative to a more aggressive approach of N management. Results at each location revealed a strong relationship between the crop fruit retention levels and N needs for the crop. This pattern was further reflected in final yield analysis as a response to the N fertilization regimes used. The higher, more aggressive, N application regimes did not benefit yields at any location. Generally, the more conservative, feedback approach to N management provided optimum yields at all locations. In 2001, a transition project evaluating the residual N effects associated with each treatment regime was initiated and no fertilizer N was applied. Therefore, all N taken-up by the crop was derived from residual soil N. In 2001 there were no significant differences among the original fertilizer N regimes in terms of residual soil NO₃⁻-N concentrations, crop growth, development, lint yield, or fiber properties. The lint yields were very uniform at each location and averaged 1500, 1100, and 850 lbs. lint/acre for Maricopa, Marana, and Safford, respectively.
38
Silvertooth, J. C., A. Galadima e E. R. Norton. "Residual Soil Nitrogen Evaluations in Irrigated Desert Soils, 2002". College of Agriculture, University of Arizona (Tucson, AZ), 2003. http://hdl.handle.net/10150/197911.
Testo completoAbstract (sommario):
Field experiments investigating N fertilizer management in irrigated cotton production have been conducted for the past 15 seasons at three Arizona locations on University of Arizona Agricultural Centers (Maricopa, MAC; Marana, MAR; and Safford, SAC). In 2002, residual N studies were conducted at two of these locations (MAC and MAR). The MAC and SAC experiments have been conducted each season since 1989 and the Marana site was initiated in 1994. The original purposes of the experiments were to test nitrogen (N) fertilization strategies and to validate and refine N fertilization recommendations for Upland (Gossypium hirsutum L.) and American Pima (G. barbadense L.) cotton. The experiments have each utilized N management tools such as pre-season soil tests for NO₃⁻-N, in-season plant tissue testing (petioles) for N fertility status, and crop monitoring to ascertain crop fruiting patterns and crop N needs. At each location, treatments varied from a conservative to a more aggressive approach of N management. Results at each location revealed a strong relationship between the crop fruit retention levels and N needs for the crop. This pattern was further reflected in final yield analysis as a response to the N fertilization regimes used. The higher, more aggressive N application regimes did not consistently benefit yields at any location. Generally, the more conservative, feedback approach to N management provided optimum yields at all locations. In 2001, a transition project evaluating the residual N effects associated with each treatment regime was initiated and no fertilizer N was applied. Therefore, all N taken-up by the crop was derived from residual soil N. In 2001, there were no significant differences among the original fertilizer N regimes in terms of residual soil NO₃⁻-N concentrations, crop growth, development, lint yield, or fiber properties. The lint yields were very uniform at each location and averaged 1500, 1100, and 850 lbs. lint/acre for MAC, MAR, and SAC, respectively. In 2002, results were very similar at the MAC and MAR locations. Trends associated with residual fertilizer N effects are not evident at either location just two seasons following N fertilizer applications.
39
Silvertooth, J. C., A. Galadima e E. R. Norton. "Residual Soil Nitrogen Evaluations in Irrigated Desert Soils, 2003". College of Agriculture, University of Arizona (Tucson, AZ), 2004. http://hdl.handle.net/10150/198133.
Testo completoAbstract (sommario):
Field experiments aimed at investigating N fertilizer management in irrigated cotton production have been conducted for the past 16 seasons at three University of Arizona Agricultural Centers (Maricopa, MAC; Marana, MAR; and Safford, SAC). In 2003, residual N studies were conducted at two of these locations (MAC and MAR). The MAC and SAC experiments have been conducted each season since 1989 and the Marana site was initiated in 1994. Original purposes of the experiments were to test nitrogen (N) fertilization strategies and to validate and refine N fertilization recommendations for Upland (Gossypium hirsutum L.) and American Pima (G. barbadense L.) cotton. Each experiment has utilized N management tools such as pre-season soil tests for NO₃⁻-N, in-season plant tissue testing (petioles) for N fertility status, and crop monitoring to ascertain crop fruiting patterns and crop N needs. At each location, treatments varied from a conservative to a more aggressive approach of N management. Results at each location revealed a strong relationship between fruit retention levels and N needs of the crop. This pattern was further reflected in the final yield analysis as a response to the N fertilization regimes used. The higher, more aggressive N application regimes did not consistently benefit yields at any location. Generally, the more conservative, feedback approach to N management provided optimum yields at all locations. In 2001, a transition project evaluating residual N effects associated with each treatment regime was initiated with no N fertilizer applied. Therefore, all N taken-up by the crop was derived from residual soil N. In 2001, 2002, and even 2003 there were no significant differences among the original fertilizer N regimes in terms of residual soil NO₃⁻-N concentrations, crop growth, development, lint yield, or fiber properties. Lint yields were very uniform at each location in 1991 and averaged 1500, 1100, and 850 lbs. lint/acre for MAC, MAR, and SAC, respectively. In 2002, results were very similar and yields averaged 1473 and 1060 lbs. lint/acre for MAC and MAR locations respectively. The results for 2003 were similar to the results of the prior two years with yields at 1322 and 1237 lbs. lint/acre for MAC and MAR, respectively. Trends associated with residual fertilizer N effects are not evident at either location following three consecutive seasons of N fertilizer treatments.
40
Silvertooth, J. C., A. Galadima e E. R. Norton. "Residual Soil Nitrogen Evaluations in Irrigated Desert Soils, 2004". College of Agriculture, University of Arizona (Tucson, AZ), 2005. http://hdl.handle.net/10150/198175.
Testo completoAbstract (sommario):
Field experiments aimed at investigating N fertilizer management in irrigated cotton production have been conducted for the past 16 seasons at three Arizona locations on University of Arizona Agricultural Centers (Maricopa, MAC; Marana, MAR; and Safford, SAC). In 2004, residual N studies were conducted at two of these locations (MAC and MAR). The MAC and SAC experiments have been conducted each season since 1989 and the Marana site was initiated in 1994. The original purposes of the experiments were to test nitrogen (N) fertilization strategies and to validate and refine N fertilization recommendations for Upland (Gossypium hirsutum L.) and American Pima (G. barbadense L.) cotton. The experiments have each utilized N management tools such as pre-season soil tests for NO₃⁻-N, in-season plant tissue testing (petioles) for N fertility status, and crop monitoring to ascertain crop fruiting patterns and crop N needs. At each location, treatments varied from a conservative to a more aggressive approach of N management. Results at each location reveal a strong relationship between the crop fruit retention levels and N needs for the crop. This pattern was further reflected in final yield analysis as a response to the N fertilization regimes used. The higher, more aggressive N application regimes did not consistently increase yields at any location. Generally, the more conservative, feedback approach to N management provided optimum yields at all locations. In 2001, a transition project evaluating the residual N effects associated with each treatment regime was initiated and no fertilizer N was applied. Therefore, all N taken-up by the crop was derived from residual soil N. In 2001, 2002, 2003 and even 2004 there were no significant differences among the original fertilizer N regimes in terms of residual soil NO₃⁻-N concentrations, crop growth, development, lint yield, or fiber properties. The lint yields were very uniform at each location in 1991 and averaged 1500, 1100, and 850 lbs. lint/acre for MAC, MAR, and SAC, respectively. In 2002, results were very similar and yields averaged at 1473 and 1060 lbs. lint/acre for MAC and MAR locations respectively. The 2003 results were not different from the prior two years of results and yields averaged at 1322 and 1237 lbs. lint/acre for MAC and MAR respectively. In 2004, yields averaged 828 and 1075 lbs. lint/acre. Trends associated with residual fertilizer N effects are not evident at either location four seasons following N fertilizer applications.
41
Silvertooth, J. C., A. Galadima e E. R. Norton. "Residual Soil Nitrogen Evaluations In Irrigated Desert Soils, 2005". College of Agriculture, University of Arizona (Tucson, AZ), 2006. http://hdl.handle.net/10150/198203.
Testo completoAbstract (sommario):
Field experiments aimed at investigating N fertilizer management in irrigated cotton production have been conducted for the past 16 seasons at three Arizona locations on University of Arizona Agricultural Centers (Maricopa, MAC; Marana, MAR; and Safford, SAC). In 2001-2005, residual N studies were conducted at two of these locations (MAC and MAR). The MAC and SAC experiments have been conducted each season since 1989 and the Marana site was initiated in 1994. The original purposes of the experiments were to test nitrogen (N) fertilization strategies and to validate and refine N fertilization recommendations for Upland (G. hirsutum L.) and American Pima (G. barbadense L.) cotton. The experiments have each utilized N management tools such as pre-season soil tests for NO₃⁻-N, in-season plant tissue testing (petioles) for N fertility status, and crop monitoring to ascertain crop fruiting patterns and crop N needs. At each location, treatments varied from a conservative to a more aggressive approach of N management. Results at each location revealed a strong relationship between the crop fruit retention levels and N needs for the crop. This pattern was further reflected in final yield analysis as a response to the N fertilization regimes used. The higher, more aggressive N application regimes did not consistently benefit yields at any location. Generally, the more conservative, feedback approach to N management provided optimum yields at all locations. In 2001, a transition project evaluating the residual N effects associated with each treatment regime was initiated and no N fertilizer was applied. Therefore, all N taken-up by the crop was assumed to be derived from residual soil N. However irrigation water analysis showed that NO₃⁻-N concentration levels added to the crop ranged from about 5-9 ppm. In 2001-2005 there were no significant differences among the original fertilizer N regimes in terms of residual soil NO₃⁻-N concentrations, crop growth, development, lint yield, or fiber properties. The lint yields were very uniform at each location and season. Trends associated with residual fertilizer N effects are not evident at either location for five seasons following N fertilizer applications.
42
Ward, Philip R. "Generation of water repellence in sands, and its amelioration by clay addition /". Adelaide, 1993. http://web4.library.adelaide.edu.au/theses/09PH/09phw262.pdf.
Testo completo
43
Franks, Carol Dawn. "Temperature, moisture and albedo properties of Arizona soils". Thesis, The University of Arizona, 1985. http://etd.library.arizona.edu/etd/GetFileServlet?file=file:///data1/pdf/etd/azu_e9791_1985_263_sip1_w.pdf&type=application/pdf.
Testo completo
44
Gottschalk, Pia. "Modelling soil organic carbon dynamics under land use and climate change". Thesis, University of Aberdeen, 2012. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=186643.
Testo completoAbstract (sommario):
Soil organic matter (SOM) models simplify the complex turnover dynamics of organic matter in soils. Stabilization mechanisms are currently thought to play a dominant role in SOM turnover but they are not explicitly accounted for in most SOM models. One study addresses the implementation of an approach to account for the stabilization mechanism of physical protection in the SOC model RothC using 13C abundance measurements in conjunction with soil size fractionation data. SOM models are increasingly used to support policy decisions on carbon (C) mitigation and credibility of model predictions move into the focus of research. A site scale, Monte Carlo based model uncertainty analysis of a SOM model was carried out. One of the major results was that uncertainty and factor importance depend on the combination of external drivers. A different approach was used with the SOM ECOSSE model to estimate uncertainties in soil organic carbon (SOC) stock changes of mineral and organic soils in Scotland. The average statistical model error from site scale evaluation was transferred to regional scale uncertainty to give an indication of the uncertainty in national scale predictions. National scale simulations were carried out subsequently to quantify SOC stock changes differentiating between organic and mineral soils and land use change types. Organic soils turned out to be most vulnerable to SOC losses in the last decades. The final study of this thesis emplyed the RothC model to simulate possible futures of global SOC stock changes under land use change and ten different climate scenarios. Land use change turned out to be of minor importance. The regionally balance between soil C inputs and decomposition leads to a diverse map of regional C gains and losses with different degrees of certainty.
45
Williamson, Derek Guthrie. "Relating release and biodegradation kinetics in soils containing aged mixtures of hydrocarbons /". Digital version accessible at:, 1998. http://wwwlib.umi.com/cr/utexas/main.
Testo completo
46
Kwong, Chin Pang. "Field and laboratory experimental study of water infiltration in cracked soil /". View abstract or full-text, 2009. http://library.ust.hk/cgi/db/thesis.pl?CIVL%202009%20KWONG.
Testo completo
47
Zhan, Liangtong. "Field and laboratory study of an unsaturated expansive soil associated with rain-induced slope instability /". View Abstract or Full-Text, 2003. http://library.ust.hk/cgi/db/thesis.pl?CIVL%202003%20ZHAN.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--Hong Kong University of Science and Technology, 2003.Includes bibliographical references (leaves 471-490). Also available in electronic version. Access restricted to campus users.
48
Miller, Kendall Mar 1958. "INTERPRETIVE SCHEME FOR MODELING THE SPATIAL VARIATION OF SOIL PROPERTIES IN 3-D (AUTOCORRELATION, STOCHASTIC, PROBABILITY)". Thesis, The University of Arizona, 1986. http://hdl.handle.net/10150/276981.
Testo completo
49
Chief, Karletta. "Soil Air Permeability and Saturated Hydraulic Conductivity: Development of Soil Corer Air Permeameter, Post-fire Soil Physical Changes, and 3D Air Flow Model in Anisotropic Soils". Diss., The University of Arizona, 2007. http://hdl.handle.net/10150/195482.
Testo completoAbstract (sommario):
Air permeability (ka) is a viable alternative to water- and texture-based methods to rapidly map saturated hydraulic conductivity (Ksat). The ability to measure this important hydraulic property without the use of more cumbersome and time-consuming methods may provide a practical approach to generate more complete data to describe hydrologic conditions. This study presents the development of an air permeameter which is suitable for desert soils. The Soil Corer Air Permeameter (SCAP) is compatible with a standard soil corer and employs digital components to measure flowrates under low-pressure gradients to improve accuracy, ease of use, and portability. SCAP allows for the extraction of undisturbed soil samples for laboratory analysis, providing direct comparisons of ka with other soil physical and hydraulic properties. The applicability of a regression equation to estimate Ksat from field-measured ka using SCAP was examined in unburned and burned soils. Ex situ field ka and laboratory Ksat measurements were compared and air to water permeability (ka/kw) ratios were calculated to determine structural changes due to water saturation. The study also characterized changes in permeability due to fire in woodland-chaparral and coniferous soils. For soils that could be extracted with minimal structural changes, results show ka and Ksat measurements for unburned and burned soils were within the 95% confidence intervals of a ka-Ksat regression developed for agricultural soils. However, correlations for in situ ka measurements in some burned soils showed a decrease in accuracy and may be attributed to soil anisotropy. A three-dimensional steady-state finite element air flow model was developed using FEMLAB 3.0A to consider the effects of anisotropy on in situ ka measurements. Results show that anisotropic conditions can introduce an error as high as a factor of 2 especially for air permeameters with high diameter to height (D/H) ratios, however, the error is much smaller than the anisotropy ratio. If anisotropy is important to characterize, it was shown that paired measurements of in situ and ex situ ka can be used to infer the anisotropy ratio.
50
Nciizah, Adornis Dakarai. "Cattle manure, scalping and soil wetness effects on some physical properties of a hardsetting soil and associated early maize growth". Thesis, University of Fort Hare, 2011. http://hdl.handle.net/10353/349.
Testo completoAbstract (sommario):
Most soils in the Eastern Cape Province, South Africa are shallow and are low in organic matter. Therefore these soils are structurally fragile and highly susceptible to inherent degradative processes like hardsetting. The objective of this study was to determine the effect of cattle manure, scalping and soil wetness on aggregate stability, penetration resistance and early maize growth in hardsetting soils. Glasshouse and field studies were conducted to determine the effect of cattle manure on aggregate stability and penetration resistance of freshly exposed topsoils by scalping at 0, 10 and 20 cm depths. In the glasshouse cattle manure was applied at 0 and 20 Mg/ha and matric suction was kept at ~ 30 and ~ 400 kPa; contrasting high and low soil wetness. Three soils were put in pots and arranged in a randomized complete block 3 2 2 factorial design. The field study was done at the University of Fort Hare research farm and the treatments were arranged in a split-plot complete randomized design with three replications. Scalping treatment was the main plot whilst the quantity of the cattle manure applied was the sub plot. Cattle manure increased mean weight diameter (MWD) by between 48% and 71% under glasshouse and between 18% and 33% under field conditions, depending on the soil wetting rate. Cattle manure reduced MWD when the soil under field condition was subjected to mechanical shaking. Soil penetration resistance decreased linearly, with increasing soil wetness but it rapidly increased with increase in matric suction up to ~200 kPa and thereafter the rate of increase reduced. In the glasshouse, all treatments had no significant effects on shoot dry weight but low matric suction increased root dry weight by 133%. Interaction of cattle manure and low matric suction reduced shoot length by 6%, shoot fresh weight by 25%, root surface area by 36%, root length by 5% and root fresh weight by 29% compared to the control. In contrast, application of cattle manure and high matric suction increased shoot length by 37%, shoot fresh weight by 136%, root surface area by 159%, root length by 94% and root fresh weight by 119%. In the field, cattle manure application increased root length density and shoot dry matter by 26% and 30% respectively. Cattle manure improved the stability of aggregates of the hardsetting soil under rapid or slow water intake conditions experienced during rainfall or irrigation. However, under field conditions cattle manure acted as a deflocculant and decreased the stability of aggregates when mechanical stress was applied. The effectiveness of cattle manure in improving maize growth in hardsetting soils was determined by matric suction.