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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

An investigation of the interaction of soil micro-organisms with special reference to the study of the bacterial population of plant root systems

Harper, John L. January 1950 (has links)
Experiments and a critical review of the literature of the technique of soil microbiology have shown that the agar plate method for the estimation of soil microbes may lead to severe errors. (1)The number of micro-organisms developing from a soil innoculum to colonies on agar media, and which are counted and used to estimate the soil population, do not always all develop. Of these organisms which can reproduce or grow on the medium provided, a proportion is not represented if the colonies are too crowded. The relationship between amount of soil innoculum and the number of colonies developing from it, is not then linear. When the development of some colonies is suppressed in this way, microbial populations estimated from the plate counts may be severely underestimated. The late developing colonies in particular are suppressed when the density of colonies on plates is high. The suppression of the development of microbial types into colonies is differential, and so changes in the degree of crowding of colonies on agar plates may bring about changes in the proportional representation of specific groups of microbes. The proportional representation of actinomycetes for example, is depressed at high densities, and yellow chromogens may be depressed or proportionately increased in different populations. It is shown that both the quantitative and qualitative effects of plating density can be attributed to microbial interaction, and that these effects are very significant within the conventional range of plating densities 70-200 colonies per 9cm. diamter plate. It is shown that there is a general relationship between the proportional representation of microbial types and the estimated total population of soils in the experimental results reported by a number of investigators. Many of the differences between rhizospheres and soil populations which have been claimed by investigators, and which show this relationship can be interpreted as plating density artifacts and it is pointed out that until many of the rhizosphere experiments which have been reported have been confirmed, making due allowance for or excluding the density effect, the results must be suspect. Statistical methods have been used to show differential rhizosphere effects (in the presence of the density effect) between three fen plants growing in peat, and between banana varieties. There is a correlation between the rhizosphere flora of the banana varieties examined and resistance to Panama disease. Within the genetic pairs Congo - Gros Michel, and Silk Fig - Guindy, the susceptible variety supports a larger microflora on its roots than the resistant. The power of the varieties to support a varied microbial flora is correlated with the size of population supported on root systems in the field. Antibacterial and antifungal substances were isolated from the rhizomes of a number of banana varieties, but no correlation with disease resistance could be found.

Molecular characterization of terrestrial organic carbon in some organic-rich soils in the northern latitudes

Swain, Eleanor Yvonne January 2013 (has links)
Northern peatlands store around one third of the global soil carbon, however over the past 100 years significant areas of these peats and peaty gley soils have been drained and planted with coniferous forest. Afforestation could accelerate peat decay due to land disturbance causing the peatland to become a net carbon source, alternatively carbon may accumulate due to increased carbon fixation, causing the peatland to remain a net carbon sink. Despite the global importance of these mechanisms, our understanding of the fate of soil carbon stores in afforested carbon-rich soils (i.e. peaty gley and peat soils) remains unclear. Peat and litter were analysed using thermally assisted hydrolysis and methylation (THM) in the presence of 13C-labelled and unlabelled tetramethylammonium hydroxide (TMAH) which revealed the distribution, degradation transformations and turnover rates of vascular plant- and Sphagnum-derived phenols in carbon-rich soil profiles. The studied sites included afforested peaty gley soils under a first- and second-rotation Sitka spruce plantation, unplanted moorland, and self seeded Sitka spruce on unprepared moorland, all of which are located in Kielder Forest, northern England. A pristine peatland in central Sweden was also extensively sampled to assess the carbon related processes occurring in carbon-rich soils prior to afforestation. The effects of afforestation on total carbon stocks were also investigated. The establishment of coniferous forests on peaty gley soils led to a net accumulation of soil carbon during the second rotation, surpassing the moorland carbon capacity. Whilst the encroachment of Sitka spruce on to open moorland via self seeding has resulted in a decreased carbon stock. The phenol composition of soil horizons displayed a maximum lignin content at deep soil across the afforested sites caused primarily by the horizon inversion that occurred prior to planting. Sphagnum acid THM products were identified across the peatland and serve as putative biomarkers for the contribution of Sphagnum-derived organic matter in peats and afforested peatlands, as well as showing potential to provide information on peatland oxic conditions. Sphagnum phenols accumulate preferentially in the anoxic saturated peat, suggesting changes introduced via land-use change or climate change could affect the water table, and thus increase the potential peat decomposition, and the subsequent loss of carbon in peatlands.

Miniature piezocene tests and effects of smear due to vertical penetration in layered soils

Sangtian, Note January 2001 (has links)
Knowledge of the soil profile is necessary for ground engineering projects and piezocones are widely used in situ test devices that can supply some of this knowledge. This thesis describes an investigation of the performance of a specific piezocone when used in thinly layered soil. A miniature piezocone, with a cross sectional area of 1 cm2, was driven at a speed of 20mm/sec into artificial layered soil samples that were constructed in the laboratory and consolidated under a vertical pressure in a 254mm diameter test cell. The layered samples contained alternating layers of pre-consolidated Speswhite kaolin clay about 20mm thick and layers of more permeable, silty or sandy soil about 2mm thick. The pore pressure filter of the piezocone was located either at the cone tip or cone shoulder. During driving, the cone resistance and pore pressure responses were recorded at a rate of at least 200 readings/sec. Once the piezocone was stopped, in a clay layer, the dissipation of excess pore water pressure was monitored. In terms of the pore pressure response, though not the cone resistance, the piezocone was able to detect the more permeable layers located between the clay layers. Both dilation and localised drainage in the more permeable layers, deformed during penetration, could have significantly influenced the pore pressure responses. Despite the proximity of permeable layers, values of the coefficient of consolidation obtained from pore pressure dissipation at the piezocone tip agreed fairly well with values obtained independently during unloading or reloading of the clay in one-dimensional consolidation tests. At the cone shoulder, the permeable layers had some influence and larger values were obtained. The layered soil samples used for piezocone testing were also used for investigating the effects of soil disturbance, or "smear", caused by vertical penetration of objects with different sectional shapes in the context of permeability measurement and soil drainage. A mandrel carrying a vertical drain, either circular (23.5mm diameter) or rectangular (50x6.5mm) in section, was driven into the centre of the soil sample at a speed of 5mm/sec. The effects of smear were evaluated by performing radial flow permeability tests in which pressure distributions across sample were recorded. The effect of smear increased substantially as the permeability of the more permeable layers increased, but only when it exceeded the permeability of the clay by a factor of about 100. For a given layer combination, the rectangular drain always produced a significantly smaller smear effect than the circular drain.

Ecotoxicology of nanoparticles : effects on plant growth and soil processes

Abdalgader, Naser January 2014 (has links)
The uptake and impact of CdS and ZnO NPs in/on maize roots and shoots was investigated and compared with their soluble bulk materials (ZnClz and CdClz). The plants were grown in Eutric Cambisol soil for 21 days. The soil was treated with seven concentrations (0.1-1.25 mg kg-I) for each metal. The Tolerance Index (T!), the Agronomical Efficiency (AE), the Bio-Concentration Ratio (BCR), the Relative Increase Percentage (RI), uptake and uptake %. were calculated for maize roots and shoots. The concentration of metals in maize roots and shoots following treatments of soil with either NPs or bulk materials increased relative to control samples. In addition, the concentration of all metals was higher in maize roots than in shoots across all metals concentrations studied. The uptake of Cd and Zn by maize roots and shoots grown in soils treated with bulk compounds was higher than for those grown in equivalent treated soil with NPs. The majority of NPs and their bulk materials had no significant negative effects on maize growth parameters. However, CdS NPs, CdClz and ZnO NPs had negative effects on the length of maize roots and shoots at the highest metal soil ratio (1.0 and 1.25 mg kg-I). The calculated maize growth parameters (TI, AE, BCR, RI, uptake and uptake %) were varied in maize roots and shoots depending on the plant part, growth period and metal treatments. The toxic effects of CdS NPs (0-100 mg L-1) and ZnO NPs (0-1000 mg L-1) on the germination and the development of maize root were studied for 8 days. The results indicated that the concentration of Zn in maize seeds and roots was higher than Cd for equivalent initial NPs concentrations. Most of the NP concentrations studied had a negative effect on the length and dry weight of maize roots. Germination of maize seed was reduced by the ZnO NPS (68.6%) more than that of CdS (58.1 %). The uptake of CdS, ZnO, and CuO NPs was also investigated for maize plants grown in Eutric Cambisol soil and hydroponic culture over 21 days. High NPs concentrations were used across both growth mediums (0.01-1.0 g kg-1 /g L-1). The TI, AE, BCR, RI, uptake and uptake % were also calculated for maize roots and shoots. The concentration of all NPs showed a similar trend of accumulation behaviour in maize roots and shoots to those found in low concentrations of NPs « 1.25 mg kg-1). The concentration of all metals in maize roots and shoots grown in nutrient solution containing NPs was higher than those grown in the NP treated soil. In addition, the impact of all NPs indicate that CuO and CdS NPs has negative effect on the length of maize roots and shoots at the highest concentrations in both cultures. Moreover, the dry weight of maize shoots was decreased by CdS NPs at the highest concentration in hydroponic culture. The calculated maize growth parameters were also varied in maize roots and shoots depending on the plant part, growth period and metal concentrations. The adsorption kinetics and desorption % of CdS, ZnO, and CuO NPs was studied on the surface of four soils using the batch method. Adsorption isotherms were evaluated by Freundlich and Langmuir model. The results of study suggest that the adsorption of all NPs increased as a function of increasing NPs concentrations until the adsorption equilibrium was reached across all soils. The relative mean adsorption of NPs in four soils was found to follow the following order: Cu > Cd >' Zn. Results also indicated that the highest adsorption of NP on soils was as follows: Libyan sandy soil> Eutric Cambisol soil > Sandy soil > Haplic podzol soil. The adsorption results for all NPs were best modelled using Freundlich equation across all soils. The kinetic behaviour of all studied NPs toward four soils showed the pseudo-second order rather than pseudo-first order kinetics. The mean desorption % of NPs in four soils was found to follow the following order: Zn > Cd > Cu. The effect of CdS, CuO, and ZnO NPs on the rate of nitrogen mineralization was investigated in Eutric Cambisol, Haplic podzol, and Sandy soil over 28 days, three concentrations of each metal NP were used (0.01-l.0 g kg-1). The influence of all test NPs on soils respiration rate was also examined for 48 hours using the same NPs concentrations above. The results of nitrogen mineralization revealed that, the concentration of nitrate (N03-) accumulated readily in three soils; however, the concentrations of ammonium (NH/), dissolved organic nitrogen (DON) and free amino acids had low levels of accumulation across all of test soil and NP types. The comparison results of NPs impact indicated that the large majority of NPs failed to reveal any significant effect upon nitrogen mineralization under any of the NP concentrations save that for amino acid concentrations. Results of soil respiration revealed that no negative significant impacts for all NPs on soil respiration across all NPs and soil types.

Spatial and statistical analysis approaches to investigate the oral bioaccessibility of potentially toxic elements in Northern Irish soils

Palmer, Sherry Beth January 2015 (has links)
Using soil samples from the Northern Ireland Tellus Survey soil archive, the oral bioaccessibility of cadmium, chromium, arsenic, nickel, lead and vanadium was measured in Northern Irish soils on a national scale. As identified by the Tellus geochemical survey, all of these elements are present at elevated concentrations in Northern Ireland soils, in some cases exceeding available human health soil screening criteria. Oral bioaccessibility testing results were combined with a pre-existing Northern Ireland oral bioaccessibility data set derived from analysis of different soil samples. From this joined data set, interpolated maps were generated to illustrate geographical trends in trace element oral bioaccessibility across the study area. Oral bioaccessibility data and previously measured geochemical variables from the same soil sample locations were then subjected to statistical analyses to underpin factors that affected trace element bioaccessibility in study area soils. Correlation analysis, factor analysis and linear regression techniques identified clay, peat, anthropogenic, igneous and sedimentary geology components each exerting unique controls over trace element oral bioaccessibility.

Soil tests for predicting nitrogen supply in Irish soils

McDonald, Noeleen Theresa January 2014 (has links)
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.

A study of the use of bentonite for reducing the permeability of soils

Barren, A. R. January 1966 (has links)
No description available.

Nutrient mobilisation in a cultivated heathland soil

Ross, Sheila M. January 1979 (has links)
The present investigation was undertaken to study the effect of the intensity of organic matter - mineral soil mixing on organic matter decomposition and nutrient mobilisation in soil intensively cultivated for afforestation. Soil mixing produced in the field by the newly developed Rotary Mouldboard Forestry Plough was simulated in laboratory incubation studies. Rates of organic matter decomposition and mobilisation of nitrogen, phosphorus, potassium, calcium and magnesium were studied in different mixing intensities of organic matter and pure quartz sand, incubated in 1 metfc tall leaching columns. Levels of mobilised nutrients were determined in fortnightly leachates. Rates of mobilisation for all five elements were found to be consistently higher in the most intensively mixed treatment with the largest surface area of organic matter exposed. When calculated on an organic matter surface area basis, nutrient mobilisation was found to be constant per unit area of organic matter surface, regardless of the total surface area in the treatment. Amounts of leached nitrogen, potassium and particularly phosphorus from organic matter and sand mixtures were higher under waterlogged conditions than when the column samples were aerated daily. Nutrient mobilisation rates for incubation samples, calculated on a field basis, showed that at the greatest mixing intensity, it might take 200 years to completely mobilise the soil nitrogen and 100 years for soil phosphorus. At this mixing intensity, potassium, calcium and magnesium might be completely mobilised in less than 50 years. 18-40% of the annual nitrogen requirement for uptake by conifers could be supplied by mobilisation of soil nitrogen in the most intensive mixture and only potassium would be mobilised at a rate exceeding tree requirement for uptake. It is suggested that a low field mixing intensity, in combination with low fertilizer inputs, could sustain acceptable yields while maintaining soil fertility for future rotations.

Donkeys and compost : intermediate transport and soil fertility management in northern Ghanaian livelihoods

Bellwood-Howard, Imogen January 2013 (has links)
Sustainable livelihoods comprise complex interactions between diverse practices, facilitated by different capital use systems. Soil Fertility Management (SFM) is one such practice. Savanna farmers use organic and inorganic soil amendments. Although a strategy integrating both is most sustainable, compost use is limited by poor access to vehicles with which to carry it. This interdisciplinary study examines how SFM interacts with transport in northern Ghanaian maize smallholders’ livelihoods. It asks how farmers could best transport compost and compares compost to fertiliser. It considers which of the five capitals described in the livelihoods framework facilitates the most appropriate SFM and transport strategies. Extending the livelihoods model, those capitals and their sources are linked to different development systems, based on capitalist, statist, participatory and traditional ideologies. Sixty farmers in two villages compared six modes of transport and the capital use systems under which they were accessed. Thirty of them similarly compared compost and fertiliser. Strong sustainability was highly relevant as crops grown with water retentive organic fertilisers consistently outperformed those fertilised inorganically. Wealthier farmers could purchase fertiliser, implying the capitalist paradigm, but most joined participatory groups through which they obtained subsidised fertiliser on credit: a mixture of participatory and state systems. Ability to use compost, however, was controlled by vehicle access. The best carriage system involved donkey carts, which were larger and could be used almost all day, and bicycles, owned by most farmers. Vehicle access was easiest when richer individuals owned large vehicles and hired or lent them to peers, combining capitalist and traditional systems. A second strategy was useful when no one in the community had enough money to purchase a vehicle. This involved participatory group ownership of large vehicles, supplemented by ownership of small vehicles that could be used at the owners’ convenience. Different systems gave access to fertiliser and transport because different contexts surrounded each. Not everyone can afford to buy fertiliser, which is a subtractable good; whereas vehicles, which are less subtractable, are increasingly available to richer individuals. The unique contribution of this thesis is to demonstrate that different access mechanisms to sustainable livelihood activities are appropriate in various contexts. However, the most successful always involve a mixture of modes or systems.

Studies on population ecology, with particular reference to soil Collembola

Usher, Michael B. January 1967 (has links)
No description available.

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