This research was carried out with the main objective of assessing the suitability of Tanzanian vermiculites as soil improvers for crop production through characterization. The research involved five samples from Tanzania and one from South Africa, which was included for comparison purposes. The results show that not all samples are vermiculites, some are hydrobiotites. Analysis shows that none of them contain hazardous accessory minerals. The samples have high cation exchange capacities (CEC) and, thus, they are suitable as soil improvers with ability to retain plant nutrients form leaching. Some have elevated concentrations of Cr and Ni, but the metals are insignificantly plant-available and do not inhibit the uptake of essential plant nutrients. Heating vermiculites above 600 °C should be avoided as it reduces the CEC by more than 90%, and makes some of the exfoliated products strongly alkaline and, thus, unfavourable for crop production. The Tanzanian vermiculites can retain plant-available water, but their ability is less than vermiculite from South Africa. The P in the vermiculites is extractable and extractability increases on heating to 200-400 °C. Application of vermiculites to the soil significantly enhanced the retention and fertilization of P. Nitrogen and K were less retained. Maize vegetative growth, dry matter yield, and nutrient uptake were significantly enhanced by amending the soil with vermiculites. Pre-heated vermiculite at 600 °C performed better than unheated vermiculite and inhibited the fixation of the applied K and N. Thus, the Tanzanian vermiculites are suitable for use as soil improvers for crop production. However, more field trials are recommended on other types of soils and crops other than sand and maize used in this research.

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This thesis presents an automated multi-electrode resistivity system which was developed for the water content characterisation of unsaturated clay soil. The system controls 64 electrodes in a fully automated procedure, offering continuous real-time data acquisition, which is one of the recent advances in resistivity instrumentation. The system was tested using a wide range of high precision reference resistors and different soils, and validated using commercial standard instruments. The results indicated a high precision, accuracy and resolution of the outputs, with a measurement error of 0.19% (maximum 0.80%) in a four-electrode method and 0.21% in an automated acquisition mode. Water content characteristics of mechanically compacted BIONICS clay soil was extensively investigated, with particular focus on the effect of wetting, drying and cracking on soil properties. It was found that the electrical resistivity of soil is sensitive to water content and compaction conditions. Experimental relationships that relate soil resistivity, volumetric water content and degree of saturation were developed. These relationships are useful to estimate the in situ water content. The resistivity behaviour of clay soils subjected to drying and wetting procedures was discussed. Soil water content and microstructure changes are key controlling parameters for resistivity behaviour. Numerical and experimental techniques were used to characterise cracking in clay soils. The results showed that cracks have anomalous high resistivity values that can be distinguished from the background, and changing cracking depth, length, width and orientation causes significant changes in soil resistivity. As the cracks form barriers that disturb the flow of electrical current, the depth and length of the crack have the major influence on soil resistivity. It was concluded that the degree of saturation or volumetric water content is a more reliable parameter than the gravimetric water content to calibrate in situ resistivity data against water content and soil resistivity can be used as a useful indicator for monitoring water content changes in clay soils subjected to drying and wetting cycles.

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The objective was to examine soi1-plant relationships on thirty soils from the Candacraig and Glenbuchat area in Aberdeenshire, Scotland, by chemical, biological and statistical techniques. Laboratory, glasshouse, and field methods of estimating soil nutrient supply to plants by measuring quantity, intensity and rate factors of elements in the soil and by making measurements on actual plants were reviewed. A classification was then made of multivariate statistical techniques and the advantages of these techniques, in particular factor analysis when used in situations in which emphasis is not on any one variable, over classical statistical techniques were discussed. A preliminary experiment to estimate the precision and accuracy of. determining Fe', Zn, Cu, Ni arid Cr by atomic absorption spectrophotometry and A1 and'Kn colorimetrically was successfully concluded. A correlation coefficient matrix based on forty six soil variables reflecting IT, P, K, Ca, Iwg, Na, Fe, En, M, Cr, Al, Zn, and Cu supply, (obtained from thirty soils series developed on parent materials ranging from acid to ultrabasic) and sixty eight plant variables (obtained from-a glasshouse experiment in which lime and fertilizer were added in a factorial treatment structure) was computed. This matrix was analysed into factors which however remained unidentified. Significant simple and multiple regression equations we re calculated, and the ' .1 effects of soil, lime, fertilizer and their interactions on nutrient contents, uptakes and dry matter production of ryegrass were shown. The following major findings emerged from the study: (I) There is a simple basic pattern of relationships to explain the complex correlation coefficient matrix in terms of six to seven factors. (II) Plant growth was predictable from measurements on the untreated soils, and the prediction of dry matter production was considerably improved when more than one soil variable was considered, (ill) The soils under study are of rather low nutrient status and respond well to complete fertilizers. (IV) Lime was very beneficial on the serpentine soils though it tended to depress yield when applied with, fertilizer on the non-serpentine soils.

One of the methods of mitigation against climate change is to offset CO2 emissions by using Carbon (C) sinks based on the Kyoto Protocol Articles 3.3 and 3.4 (UNFCCC 1997). One potential C sink is the terrestrial soil organic carbon (SOC) pool which can be affected by a wide variety of environmental factors across a range of time and spatial scales. Soil carbon models RothC, DNDC, Century and the IPCC method were assessed and compared to measured site data in order to determine accuracy. Simpler models such as RothC and the IPCC method were found to perform better [In the absence of abundant input data]. The uncertainty of these models was assessed and found to be +/-15% for the RothC model, +/-19% for the DNDC model and +/-26% for the Century model all with 95% confidence. Post-hoc application of mitigation factors were derived using the IPCC method to provide estimates of carbon mitigation potential. These were applied on a pan-European scale using projected land-use changes. The estimates were compared to trends simulated using an adapted regional scale version of the RothC model, which estimated that 3.1% (+/-0.5%) of the 8% Kyoto EU 15 emissions reduction target (from 1990 levels) could be achieved using these measures.

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