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Cassiterite extraction in West Malaysia has left a legacy of some 80,000 hectares of nutrient-poor, drought-prone, quartz sandy tailings. Their proximity to urban centres has long made them a target for agricultural and forestry enterprises, and various techniques have been developed to overcome their intractability, including amendment with bulky organic matter and replacement with natural soils. Although reasonably successful, these approaches have often failed to acknowledge that a percentage of the original heavy mineral suite remains in sandy tailings, exerting possible phytotoxic effects and certainly raising concerns about the suitability of sandy tailings for agronomic crop production. To determine the nature and extent of trace element contamination of sandy tailings, ten different areas were identified and sampled in the states of Selangor and Perak. Preliminary analyses failed to corroborate earlier discoveries of elevated mercury and cadmium status, but lead, zinc, arsenic, uranium and rare earth elements were all common. However, greater concentrations of all these elements were found in clay (slime) tailings, which had been colonized by dense vegetation cover. This indicated that levels of trace elements in sandy tailings were not of themselves phytotoxic, but in the context of reduced nutrient availability, might exert a disproportionate influence on their colonization by plants. The colonization of sandy tailings by Melastoma malabathricum was therefore examined, revealing that in two of four sites, water contents were greater in colonized areas than the rest of each site. Macronutrient concentrations were also greater in colonized tailings, as were concentrations of zinc and manganese, but whether these were the cause or result of plant establishment could not be determined conclusively. Overall, trace element distribution in sandy tailings did not influence colonization by Melastoma, although in three of four populations, foliar concentrations of uranium were greater than those of a population growing on a natural soil. This has serious implications for the agronomic use of sandy tailings. The effects of bulky organic and clay amendment of sandy tailings on the availability and uptake of trace elements has never before been examined. A tropical greenhouse experiment was undertaken to examine the effects of peat and clay on the growth and trace element chemistry of Panicum miliaceum and Pueraria phaseoloides. The use of symbiotic mycorrhizal fungi was also included, since although these often improve the phosphorus nutrition of their hosts, they might also increase trace element uptake from pools sorbed by organic matter. Neither clay nor peat improved the growth of either plant species. However, addition of clay substantially increased the availability of aluminium and trace elements, and its use in rehabilitation attempts cannot be recommended. In contrast, peat reduced the availability of Co, Cu, As, La, Ce and U, whilst simultaneously improving the ECEC of sandy tailings. The effects of mycorrhizal inoculation were difficult to interpret, since the carrier medium used (predominantly zeolite) drastically altered the chemistry of soils to which it was added. Growth of Panicum and Pueraria was equally poor on two of three naturally sandy soils. Adding peat to sandy tailings produced plants with similar foliar chemistry to those grown on natural soils, suggesting that plant communities established on these natural siliceous media could act as models for the sustainable rehabilitation of anthropic mine tailings - something which has never before been suggested. A range of native species are recommended as having potential for further research into naturalistic rehabilitation.

The introductory chapter presents a review of the chemical, physical and biological properties of colliery spoil, and the problems which they represent to reclamation and revegetation. The general approaches already cited in the literature for overcoming such problems are looked at as well as the varying managerial practices and after uses that are often employed. This is followed by a brief description of the field trials at Baads, Riddochhill and Loganlea and includes the rationale behind the choice of organic amendments, their suitability and supply. A number of problems resulting in poor establishment in the latter two trials are also discussed. The build-up of organic matter in the spoil is of great importance to successful reclamation as it improves the physical structure of the material and is the major source of long-term nutrient supply to any established vegetation. Chapter 3 considers the use of the most common chemical methods for the determination of organic matter and organic carbon and shows them to be unsuitable because of the high level of background carbon in the unburnt shale preventing the unambiguous measurement of the build-up of carbon from plant and microbial sources. More successful was the measurement of carbon turnover, estimated by carbon dioxide evolution. This gave comparative figures for "biological activity" and carbon turnover in spoils which received different treatments. Although the carbon turnover in the treated spoils was similar, there was considerable litter accumulation at the spoil surface which varied greatly between amendments. All the spoils showed a high level of carbon turnover, especially when compared to nitrogen and phosphorus. Chapter 4 deals with the levels, distribution and turnover of the macronutrients nitrogen, phosphorus and potassium. Nitrogen and phosphorus are particularly important as they are usually deficient in colliery spoil. Measurements of nitrogen, phosphorus and potassium in the herbage, litter and spoil were made to determine how much of a nutrient capital had been accumulated in the system, and where it was located. The ability of the spoil to supply nutrients was assessed by mineralisation experiments. Information was also obtained on nitrogen cycling by measurement of nitrification. The results of these experiments confirmed that the colliery spoil was deficient in nitrogen and phosphorus, with the exception of the chicken manure treated spoil which contained appreciable amounts of available phosphate, and that little of these nutrients was being supplied. A small fertiliser response trial was set up which showed that vegetation established on reclaimed colliery spoil responded rapidly to the supply of nitrogen, but not phosphate and potassium. A brief, concluding chapter discusses management practices in the light of the experimental results described previously.

It is proposed that microbial polysaccharides behave anion-exclusively, permitting the transport of cations, but excluding the diffusion of anions. This hypothesis has been investigated in the context of polysaccharides produced by microorganisms in the rhizosphere. The anion-exclusive behaviour of exopolysaccharides, extracted from broth cultures of a range of rhizosphere microorganisms together with several commercial polysaccharides (i.e., xanthan, scleroglucan, dextran, guar gum) was investigated by measuring the electrochemical potential which developed as a result of the diffusion of KC1 across a polymer layer. Considering xanthan as a 'model' microbial polysaccharide, polymer concentration, layer thickness and the presence of either O-acetyl or pyruvyl groups were found to positively affect the degree of anion exclusion. The anion-exclusive behaviour of xanthan was verified by direct ion analysis of solutions either side of the polymer layer. It was found that in a range of ionic environments, the diffusion of anions was reduced by ~70% by the presence of a 3% w/w xanthan layer. The influence of xanthan on the diffusion of cations was studied using magnetic resonance imaging. In contrast to the proposed theory of anion exclusion, the rate of cation (Mn2+) diffusion through a 3% w/w xanthan layer was found not to be greater than that through free aqueous solution. The possible occurrence of anion exclusion and consequences thereof in the rhizosphere were assessed by studying the effect of substitution of the water films in soil with a layer of 3% xanthan on the growth of wheat seedlings. The phosphate, but not potassium content of those plants grown in soil with xanthan was ~20% lower than in the control plants. Those plants grown in xanthan-amended soil produced ~30% more biomass by dry weight. The anion-exclusive properties of polysaccharides produced naturally in bulk soil, the rhizosphere and root surface of pea was studied by the measurement of diffusion potentials. All three were found to show a high level of anion exclusion. The influence of O-acetyl groups in xanthan on the rate of water transport and degree of water binding was studied using stray field NMR methods. It was found that removal of O-acetyl groups reduces the rate of water transport and increases the rate of water binding at any given xanthan concentration. It is proposed that microoganisms produce anion-exclusive polysaccharides in the rhizosphere to protect themselves against the potentially lethal effects of water stress.

Previous work has suggested that soil conditioners can provide environmentally beneficial aids to agriculture and soil conservation. To investigate this further, studies were carried out on soil conditioner effects on soil erosion, soil structure and crop performance. The main soil conditioner investigated was an anionic, hydrophilic conditioner based on ammoniurn-laureth-sulphate. Several objectives were established, in order to test the hypothesis that ammonium-laureth-sulphate can establish treatment effects by decreasing soil erosion and improving soil structure and crop performance. Subsequently, initial attempts were made to elucidate the mode of action. The field experiments were established on loamy sand soil (Bridgnorth series) at the Hilton Experimental Site, east Shropshire and on sandy silt loam soil (Salwick series) at the Plant and Environment Research Unit at Compton Park, Wolverhampton. The main soil conditioner applied was 'Agri-SC' at manufacturer recommended application rates and three other soil conditioners were used for some comparative studies. Following applications of ammonium-laureth-sulphate to bare and cropped plots, effects on the topsoil (0-5 cm) included significantly decreased bulk-densities, soil moisture contents and splash erosion and significantly increased soil porosity and infiltration rates. Other effects included decreased runoff and erosion rates from 100 slopes and penetrometer resistance and increased aggregate stability and drainage capacities. Responses in a winter wheat crop (cv. Beaver) included apparent suppressed seedling emergence, followed by apparent enhanced growth and development. Initial laboratory studies indicated conditioner treatment altered cation exchange capacities, mineral and elemental compositions and provided evidence for chemical interparticle bonds. ' The soil conditioner appeared to function through a mechanism involving several stages. Upon application, the charged polymer molecules were electrostatically attracted to clay or silt particles and their attached ions. It is postulated that ammonium ions could then replace Ca and possibly Mg and Na, causing the polymer molecules to adhere to soil particles. This might be associated with mineral deposition. The laureth polymer strings could thus bridge individual particles and increase internal aggregate stability. This mechanism may be relevant for further understanding of the mode of action of other hydrophilic, polymer-based soil conditioners.

The object of this research programme was to investigate the stability of a silty clay under undrained repeated loading. Equipment has been designed and developed for the application of a quasi-sinusoidal compressive load form to triaxial samples. A series of monotonic strain controlled triaxial tests with pore pressure measurement was performed on normally consolidated and overconsolidated samples of saturated reconstituted Keuper Marl. These tests defined the critical state parameters, and hence the stable state boundary surface for this soil, and provided a basis for a comparison with the results of cyclic stress controlled triaxial tests. Two series of cyclic triaxial compression tests were performed: firstly, single stage tests using a constant level of repeated stress; and secondly, multistage tests. These aimed to investigate: a) stress conditions at failure under cyclic loading; b) strength of non-failed samples after cyclic loading; and c) strain and pore pressure behaviour under repeated loading. Criteria for the stability of a soil under cyclic loading are presented and a model is developed based on the pore pressure behaviour of the soil under repeated loading. This model can be used to predict pore pressures and failure for normally consolidated and lightly overconsolidated soils.