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In agricultural production, disturbance of the soil by cultivation occurs regularly. Mechanical energy applied in this way can have a adverse effect on soil stability, a lowering of soil organic matter (S_OM), and a increase in CO2 emissions. These changes result in unwanted environmental consequences and compromise the ability of soil to maintain a competitive and sustainable agricultural industry. As agricultural systems evolve, it becomes important to develop a indication of their sustainability with regard to soil structure, well before any serious consequences become apparent. The am of this work was to quantify the effect of mechanical energy (in particular tillage) on soil structural stability and the loss of SOM. New laboratory techniques were devised in which mechanical energy was applied to a range of soils at different water contents with measurements made of stability and the mineralization of SOM. Techniques used for characterising stability involved measuring mechanically-dispersed clay, cm using a turbid metric technique and the proportion of water stable aggregates (>250 m). A re-examination of the statistical theory of brittle fracture showed that soil friability, F1, could be quantised using the coincident of Variation of tensile-strength of a population of similar sized aggregates. Specific energies associated with different cultivation practices, were simulated using a falling weight and results indicated that the sensitivity of soil to mechanical damage was essentially zero at soil water contents below the plastic limit (wpL). With increasing soil water content, sensitivity to destabilization increased sharply. The empirical model to characterise these phenomena was evaluated under field conditions where the energy consumption of different tillage implements, operating at different soil water contents, was measured directly. Good agreement between the level of destabilization measured in the field and those in the laboratory was obtained at similar specific energy values. C.W. Watts, 2003. Cranfield University, Silsoe. The field experiments also showed that increased levels of cm following tillage were responsible for stronger and less friable day aggregates. More experiments on a soil with SOC values ranging from all to 32 g/kg enabled the original model to be refined, linking cm, SOC and soil water content to disruptive energy. This led to the development of a index, S, which quantise the sensitivity of soil to destabilization by mechanical energy inputs and provides a method for identifying soils at risk. The effect of mechanical energy on the mineralization of SOC was measured using the falling-weight. Mineralization was characterised by measuring soil respiration using data-logging, conductinetric respirometers, built to monitor CO2 emissions following applications of mechanical energy. Changes in respiration were characterised by the respiration ratio, rr (defied a respiration following the application of energy divided by basal respiration). Higher values of, rr, were associated with greater energy levels, particularly on soils with lower SOC. Increased respiration was also measured following tillage in the field, particularly from soils following tillage at high energy levels where the effect lasted for several weeks. In this work three physically based measures of soil quality (S, F1 and rr) have been used to quantify the effects of tillage of different intensities on soil structural stability and the loss of organic matter. Parameters common to these measures of soil quality are SOC content, soil-water content and tillage intensity. Results of this work indicate that organic matter, physically protected by stable soil structures, can b exposed to mineralization when the structure in destabilized during tillage, particularly a the soil becomes wetter (w>w1ºL). The practical consequences of this work concluded that increasing the levels of SOC, cultivating the soil at water contents below the plastic limit and a reduced energy input, provide the best practical approach to maintaining soil physical quality. The new methodologies developed here have helped improve understanding of the effects of mechanical energy on soil structural condition. They provide a sound basis to answer a range of questions relating to soil physical quality and the consequences of different soil management practices for soil behaviour in the environment, thus enabling the boundaries between good and bad practices to b better defied.

Soil compaction has been described as the most serious environmental problem caused by conventional agriculture, as it results in several stresses which may interact simultaneously, including increased soil strength, decreased aeration and reduced hydraulic conductivity. Root system architecture (RSA) is the arrangement of roots within the soil matrix and is important because the specific deployment of roots within the soil can determine soil exploration and resource uptake. As roots deliver water and nutrients to growing plants, whilst also providing anchorage, their importance cannot be overstated. Yet, our understanding of how roots interact with the surrounding soil, especially at the micro-scale level, remains limited because soil is an opaque medium, so preventing roots from being visualised without disturbing them. Destructive techniques are commonly employed for the analysis of RSA, however this can result in the loss of key information concerning root architecture, such as elongation rates and root angles and important soil characteristics such as soil structure and pore connectivity. However, X-ray Computed Tomography (CT) has been shown to be a promising technique for visualising RSA in an undisturbed manner. The species considered in this thesis were wheat (Triticum aestivum L.) and tomato (Solanum lycopersicum L.). Further information regarding the response of roots to soil compaction has been achieved through the use of X-ray CT, automatic root tracing software and novel image analysis procedures. Soil compaction significantly affected root length, volume, surface area, angle, diameter, elongation rates and root path tortuosity, however the influence of soil texture on root responses to soil compaction was significant. Moderate compaction benefits root growth in clay soil, possibly due to the greater nutrient and water holding capacity, but adversely affected root growth in loamy sand. The results suggest that there is an optimum level of soil compaction for the different soil types. Roots elongated rapidly between 2-3 days after germination (DAG), it is hypothesised that is related to the mobilization of seed storage substances to the growing roots. The use of transgenic mutants of tomato with altered levels of abscisic acid (ABA) has provided a greater insight into the role of ABA in mediating root responses to soil compaction. This work will enable better phenotyping of plant varieties with enhanced root system traits for resource foraging and uptake. Knowledge of the responses of root systems in heterogeneous soil is vital to validate root phenotypes and overcome future food security challenges.

The principal objective of archaeology is to reconstruct in all possible ways the life of a community at a specific physical location throughout a specific time period. Distinctly separate layers of soil provide evidence for a specific time period. Discovered artefacts are most frequently used to date the layer. An artefact taken out of context is virtually worthless; hence the correct registration of the layer in which they were uncovered is of great importance. The most popular way to record temporal relationships between stratigraphic layers is through the use of the 2D Harris Matrix method. Without accurate 3D spatial recording of the layers, it is difficult if not impossible, to form new stratigraphic correspondences or correlations. New techniques for archaeological recording, reconstruction, visualisation and interpretation in 3D space are described in these works and as a result software has been developed. Within the developed software system, legacy stratigraphy data, reconstructed from archaeological notebooks can be integrated with contemporary photogrammetric models and theodolite point data representations to provide as comprehensive a reconstruction as possible. The new methods developed from this research have the capability to illustrate the progression of the excavation over time. This is made possible after the entry of only two or more strata. Sophisticated, yet easy-to-use tools allow the navigation of the entire site in 3D. Through the use of an animation-bar it is possible to replay through time both the excavation period and the occupation period, that is to say the various time periods in antiquity when human beings occupied these locations. The lack of complete and consistent recording of the soil layers was an issue that proved to be an obstacle for complete reconstruction during the development of these methods. A lack of worldwide archaeological consensus on the methods of stratigraphic recording inhibited development of a universal scientific tool. As a result, new recording methods are suggested to allow more scientific stratigraphic reconstruction.

Comprised of the author's previously published works / Includes bibliographical references / 1 v. (various pagings) : / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (D. Sc.)--University of Adelaide, Dept. of Soil Science, Waite Agricultural Research Institute, 1988?