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.