School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemThe reactions and availability of manganese in soils( 1969)The reactions of Mn in soils and the relationships between these reactions and the mechanisms of supply of Mn to plants have received attention from scientists over the last 40 years; most attention being given to the problem of Mn deficiency which occurs most commonly in soils with pH's from 6.5 to 8.0. The term "neutral" soils will be used throughout this thesis for these soils on which in deficiency occurs; the term is just as meaningful as and less cumbersome than the term "neutral and alkaline soils" which is commonly used. Some significant contributions have been made to our knowledge of the availability of In in neutral soils, but the progress has been unduly slow. It would appear that the slow progress can be partly attributed to the perpetuation of poor work, and thinking, not only by some workers in the subject, but by some writers of textbooks. This is a serious allegation to make, but when one becomes intimately involved in the subject, one is confronted with many pieces of work which are incompatible and mutually contradictory. The commonly accepted reason for In deficiency is the microbial oxidation of divalent In to higher in oxides, and yet many workers are obviously not aware of evidence which makes this conventional theory look absurd. The two simple facts that microbial oxidation of divalent Mn occurs in all neutral soils and that Mn deficiency is a "disease" of the wetter and cooler climates of the world illustrate my point precisely. This unsatisfactory situation calls for a critical appraisal of the existing theories, and in this thesis I have attempted to do this and to give a clear account of the subject. The reader will quickly find, however, that here we have a very complicated problem to which we only know some of the answers. In this thesis reference is made to some "local" soils, namely: Corny Point, Dooen, Hallam, Mt. Gambier, Penola Hill, Penola Flat, Rendelsham, University, Walpeup, Werribee, and Yambuk. And, for the convenience of the reader, some of the relevant properties of these soils are described in Part IV - Experimental Methods and Description of Soils, pp.252-255. The Introduction is not a complete review of all the work which has been done on Mn in soils. It is deliberately selective and obviously some work is irrelevant here, but some other work has been omitted either because it is mere duplication or because it does not warrant perpetuation; though possibly some work, which is relevant or otherwise, may have been overlooked. The early part of the Introduction outlines our present knowledge of the reactions and availability of in in neutral soils. This is followed by an attempt to define the nature of the root surface, a subject which has received little attention in relation to soils and has considerable relevance in the mechanism of uptake of in from neutral soils. The experimental work covers several aspects of Mn in soils, namely: the microbial oxidation of Nn, the reversion of available forms of in and the uptake of Mn by contact reduction. The results and discussions of the experiments indicate forcefully the extreme complexity of the problem of the availability of In in neutral soils. And, possibly just as important, they indicate that in a few years, one person cannot possibly solve a problem which has been baffling scientists for decades.
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ItemThe dynamics of growth in even-aged stands of Eucalyptus obliqua (l'herit)( 1968)The genus Eucalyptus contains a large number of species suitable for the commercial production of timber, but the history of their forest management is comparatively recent, being initially founded on traditional European experience. Despite this tradition and the fact that many species have certain silvicultural properties in common distinguishing them from other timber producing genera (Jacobs, 1955), there already exists a diversity in silvicultural systems, even for the one species or species association in a single region. This diversity appears to be associated with the development history of the forest region, because there has been a general tendency to perpetuate the characteristic forest structure of a particular area at the time that planned management was commenced. This structure has varied from extensive areas of even-aged stands of a single species to intimate mixtures of species of all ages and sizes in association. The variation in forest structure appears to have developed largely from a diversity in the history of settlement and early exploitation. Fire history, access history, intensity and frequency of past utilization have all played a prominent role in forming the characteristic forest structure of a particular area. Regardless of whether growing in regular or irregular forests, the determination of tree and stand age for the majority of eucalypts is extremely difficult or even impossible. The identification of annual rings is reasonably reliable only for those species growing in subalpine and alpine climatic zones of Australia. Therefore, in the absence of adequate compartment and stand history records, management planning in the eucalypts must be based on methods which do not require precise knowledge of tree and stand age. While age is not normally required for the management of irregular forests, it has been fundamental to the planned management of even-aged forests. The ability to distinguish sites of differing productive capacities is an important aid in forest management. The most popular method of site classification is the site index, which gives stand height at a particular reference age. If age is unknown this method cannot be used and alternative methods of site quality determination have not yet been developed for the eucalypts. (From Introduction)