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Air-filled porosity (AFP) affected the suppressiveness of organically based plant growth media against Pythium ultimum infection. AFP also interacted with microbial activity, moisture levels altered by covering/uncovering media and water severity of pythium damping-off. It has not been possible to determine a narrow range of AFP required to achieve consistently suppressive media, as AFP has been found to interact with many factors such as microbial activity, temperature shock of media and plants and moisture levels modified by covering and uncovering media, or using different pot heights to modify WHC. The use of different batches of compost and ageing of compost in the seven experiments reported here may also account for some of the different effects of AFP on the severity of Pythium disease. It is not recommended that AFP be used for controlling Pythium damping-off, unless certain conditions, such as microbial activity, can be controlled to a range of specifications also. Variability of compost is one of the principal factors limiting its widespread use, so therefore, improving the quality control during the composting process would be the principal factor which should be investigated in future. / Master of Science (Hons)

Typewritten copy Includes bibliographical references The measurement of soil moisture in situ is called Part A; The study of soil moisture changes under a simple crop rotation is called Part B. Evaluates the Bouyoucos electrical resistance method of measuring soil moisture in situ; and studies the soil moisture under a simple crop rotation. Has been the subject of 2 papers entiled: Techniques associated with the use of gypsum block soil moisture meters / Aitchinson, Butler and Gurr; and, Gypsum block moisture meters as instruments for the measurement of tension in soil water / Aitchinson and Butler. The papers are attached. Part A includes a brief summary and discussion of these papers

Near infrared spectroscopy (NIS) has been used routinely for many years for the measurement of grain protein and moisture in plant breeding programmes. Investigation as to the applicability of NIS to the identification from a barley breeding programme of the progeny with high malting quality potential was carried out over several harvests. The project concentrated on the determination of correlations between Hot Water Extract, Total Soluble Nitrogen, and Free Alpha Amino Nitrogen contents of worts (the extract of malt used to make beer) and NIR transmission data using the multivariate method of partial least squares regression. The correlation coefficients, for both calibration and prediction data sets, were significant and the standard error of prediction was similar to that obtained in the standard methods in the first year, but were unsatisfactory in the second. The instrument chosen for the study gave satisfactory correlations for the purpose of selection in the intermediate generations of the breeding programme with errors similar to the analytical methods, as long as a very wide range of calibration samples were collected from more than one harvest. It was shown that the use of an NIR spectrophotometer as a selection tool for malting quality within a barley breeding programme would not be sufficient to justify investment in this type of instrument for this purpose alone. / Master of Science (Hons)

Knowledge of the stress-strain relationship of the compacted soils in tension is of importance for understanding of cracking that occurs in earth structures, in particular embankment dams and landfill barriers. Understanding the correlation between tensile properties and traditional soil parameters and soil suction is essential in identifying problems associated with desiccation induced cracking. A series of extensive laboratory experiments were performed on three different soils from existing embankment dams. This thesis concentrated on the investigation of tensile strength in relation to the type of soil, compaction water content, compaction density ratio, rate of loading, soil suction, moisture retention characteristics and the effect of drying and wetting. Stress-strain behaviour and tensile properties indicated a dependence on soil type and compaction criteria. The plasticity index, clay content and type of mineral has shown a significant influence on tensile strength. Compaction dry of optimum resulted in an increase in strength. Compaction wet of optimum showed a decrease in strength and small increase in strain at failure. Higher compaction effort resulted in higher tensile strength, tensile stiffness and brittle stress-strain behaviour. Difference in loading rate revealed response time for initial tensile deformation as well as sustainable duration up to failure point. The effect of soil suction plays an important role in drying during which specimens exhibited a considerable strength increase. The magnitude of strength increase may have been contributed by a combination of suction, air entry value and compaction density. The effect of wetting could cause decreasing in suction and thus a reduction in strength. Based on the findings, it was concluded that the desiccation-induced may not necessarily occur due to an associated increase in tensile strength. However, an increase in tensile strength is likely to be accompanied by an increase in shrinkage. Therefore, desiccation-induced cracking is related to the interaction between moisture loss, change in soil suction, tensile stress and shrinkage.

The problem of cavity expansion in unsaturated soils is investigated. A unified constitutive model for unsaturated soils is presented in a critical state framework using the concepts of effective stress and bounding surface plasticity theory. Consideration is given to the effects of suction and particle crushing in the definition of the critical state. A simple isotropic elastic rule is adopted. A loading surface and bounding surface of the same shape are defined using simple and versatile functions. A limiting isotropic compression line exists, towards which the stress trajectories of all isotropic compression load paths approach. A non-associated flow rule is assumed for all soil types. Isotropic hardening/softening occurs due to changes in plastic volumetric strains as well as suction for some unsaturated soils, enabling account of the phenomenon of volumetric collapse upon wetting. Results of isotropic compression tests, oedometric compression tests and drained and undrained triaxial compression tests performed on Kurnell (quartz) sand in saturated and unsaturated states and subjected to stresses sufficient to cause particle crushing are presented and used to calibrate the model. The model is also calibrated using results reported in the literature for triaxial tests performed on saturated and unsaturated speswhite kaolin and three load paths. For both soils the model leads to a much improved fit between simulation and experiment compared to that for models based on conventional plasticity theory. The model is implemented into a cavity expansion analysis using the similarity technique, extended for application to unsaturated soils. Cylindrical and spherical cavities are considered, as are drained and undrained conditions. Cavity expansion results for the bounding surface model and conventional plasticity models are compared for saturated conditions. Substantial differences highlight the importance of adopting a model that accurately describes stress-strain behaviour. Cavity expansion results for the bounding surface model and saturated and unsaturated conditions are also compared. Substantial differences, particularly in the limit pressure, highlight the major influence of suction and the importance of accounting for this when using cavity expansion theory to interpret results of the cone penetration and pressuremeter tests.

Thesis (Ph. D.)--Oregon State University, 1964. / Typescript. Mounted photographs. Includes bibliographical references (leaves 99-109). Also available on the World Wide Web.

Both transportation costs and market values of woody biomass are strongly linked to the amount of moisture in the woody biomass. Therefore, managing moisture in the woody biomass well can lead to significant advantages in the woody biomass energy business. In this study, two prediction models were developed to estimate moisture content for Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) and hybrid poplar (Populus spp.) woody biomass. Experimental data for the Douglas-fir model were collected over four different seasons at two different in-forest study sites in Oregon (Corvallis and Butte Falls) between December 2010 and December 2011. Three woody biomass bundles consisting of 3-meter length logs (30 to 385 mm diameter) were built each season at each study site; a total of 24 Douglas-fir bundles (1,316 to 3,621 kg weight) were built over the period. Experimental data for the hybrid poplar model were collected in two drying trials at two off-forest study sites in Oregon (Clatskanie and Boardman) between April 2011 and January 2012. Two types of woody bundles consisting of 3-meter length logs were built each trial: small (28 to 128 mm diameter, 2,268 to 5,389 kg weight) and large (75 to 230 mm diameter, 3,901 to 7,013 kg weight). A total of eight hybrid poplar bundles were built over the period. These data were used to develop linear mixed effects multiple regression models for predicting the moisture content of Douglas-fir and hybrid poplar biomass, respectively. The major factors considered in this study for predicting woody biomass moisture content change were cumulative precipitation, evapotranspiration (ET₀), and biomass piece size. The Food and Agriculture Organization (FAO) Penman-Monteith method, which requires temperature, solar radiation, wind, and relative humidity data, was used to calculate ET₀. The developed models can be easily applied to any location where historic weather data are available to calculate estimated air-drying times for Douglas-fir and hybrid poplar biomass at any time of the year. Oregon has been split into nine climate zones. Use of the model was demonstrated for four climate zones, two in which air-drying data were collected, and two in which it was not collected. Considerable differences in predicted drying times were observed between the four climate zones. / Graduation date: 2013

Graduation date: 1996

Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2007. / Includes bibliographical references. Also available in electronic version.