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lateritic gravel, phosphorus, soil properties, phosphorus buffering


This study aimed at investigating the distributive patterns and properties of lateritic gravels at "Yalanbee" (C.S.I.R.O. research station) and how these properties and patterns e ffect the adsorption of phosphorus onto the lateritic gravels. It also aimed partly at investigating the effect of the presence of lateritic gravels on the adsorption of phosphate by "whole soils". Gravels in the Yalanbee soil had migrated since their formation as was shown by their abundance and large size at the top of a slope which graded to less abundant, smaller and more rounded gravels further down the s lope. The distribution of gravels in the Malebelling soil was not associated with the landscape but showed the same relationship between abundance and size. A region of soil with a low percentage of gravel (10%) exhibited on abundance of smaller gravels (2.0-4.0rnrn) whilst a region of soil with a high percentage of gravel (>40%) exhibited gravels mainly of a size greater than 4.0rnrn. The pattern of distribution of Kojonup bog-iron was related to the proximity of a water course. Differences were found in shape, colour, fabric and texture of the gravels under study. Mineralogical differences were found using x-ray diffraction. The main difference was the presence of secondary forms of aluminium (gibbsite and boehmite) in Yalanbee soils and its general absence in Malebelling and Kojonup soils. The crystal size and composition of minerals did not vary with the landscape, however the mineral types present did. Lateritic gravels do adsorb phosphate. This adsorption is generally on the outer surface as shown through autoradiography and the amount adsorbed increases with smaller sized gravels as borne out in phosphate adsorption experiments . The amount of phosphate adsorbed by Malebelling gravel s after five weeks was greater than that adsorbed by Yalanbee and Ko jonup gravels of the same size distribution. Electron microscope work suggested that this high adsorption was due to the nature of the surface and to the possibility that a porous structure is associated with these gravels as evidenced by fungal and bacterial activity inside the gravel. The adsorption of phosphate onto "whole soils" was greatly effected by the abundance and size of gravel present. The adsorption at all levels of phosphate after 24 hours and five weeks for most samples was reduced according to the abundance and size of gravel present.


University of Western Australia Undergraduate Thesis

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