Thesis (Ph.D.)(Agricultural Economics)--University of Pretoria, 2007. / Includes summary. Includes bibliographical references. Available on the Internet via the World Wide Web.

The aim of this study was to explore how land degradation influences the living conditions of a farming community in Kenya. Investigation method used was qualitative research and data collection through semi -structured interviews with chosen farmers, interview with a professional in the relevant profession, and field observation within a farming community in central province of Kenya. In developing countries many families live in rural areas and depend on small scale farming for livelihood. These communities are however faced with poverty from degraded lands as is indicated by the interviews conducted in this rural community where farming activities has resulted in degradation of land. Unhealthy agricultural practices threaten human survival by not only eating innutritious food, but reduction in economic capability, as well as causing loss of biodiversity which is indispensable for environmental sustainability.

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This thesis investigates the use of CO2 laser radiation to treat concrete surfaces. Specimens were treated with varying laser parameters, and the resultant surfaces were analysed mechanically and chemically. A glass was formed by laser interaction, with underlying decomposition of both the cement paste and aggregate. The application of a cement-based coating prior to processing protects the concrete from excessive temperature rises during treatment. Processing of the coated material resulted in a glazed surface with no decomposition of the concrete substrate. With low energy density, OPC concrete exhibits only surface dehydration. However, when the energy density is increased, a glassy layer, with surrounding and underlying dehydration, is formed. Increasing the spot size results in a change in behaviour when the material is laser treated: several mm of concrete are removed, leaving either rough, bare concrete or a glazed trench. The resulting surface condition is dependent on the laser power. Thermal analysis techniques were used to identify the degradation reactions and the temperatures at which they occur during laser treatment. These are dehydration of the ettringite and ferrite phases at 1149C, dehydration of Ca(OH)2 at 462C, decarbonation of CaCO3 and ejection of material from 8129C onwards and the formation of a fiised glass layer at 1283 `C. The strength of attachment of the glass to the concrete decreases with increasing power or decreasing traverse speed due to the dehydration of the underlying material. The strength also decreases with time after treatment, due to rehydration of CaO. Mechanical failure occurs several mm below the glassy area into the dehydrated substrate, where dehydration of Ca(OH)2 has caused disruption to the structure of the material. The temperature rise in the material was monitored using embedded thermocouples at various depths. A one dimensional theoretical model agrees well with the experimental results over only a limited range of depth and time. A three dimensional finite difference model shows close agreement with experimental results over a range of operating parameters equivalent to those determined experimentally. Operating maps were generated which predict the depths to which the identified reactions occur. II A combination of pozzolanic Portland cement, chamotte, sand and waterglass can be successfully applied to the concrete surface. It acts both as a thermal insulator and provides vitrifiable material for laser treatment. Low power levels drive water out of the coating resulting in dehydration and colour changes, whilst higher power levels result in the formation of a glass on the coating surface. The attachment of the glass shows an area of maximum strength when power levels are below 150 Watts and traverse speeds below 2mm/s. Beyond these parameters the attachment becomes progressively weaker. Thermal analysis of the coating material shows no evidence of Ca(OH)2 dehydration and no decarbonation, resulting in no ejection of material. The underlying concrete is unheated, and therefore undergoes no decomposition reactions. Mechanical failure occurs at the limit of the glassy region rather than several mm below it as with bare concrete. Thus, the weakest point is the interface of the glazed-unglazed regions now that no significant Ca(OH)2 dehydration occurs.

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This research seeks to explore the complexity of human-land relations in the Aspre, with respect to land degradation. It is argued that in human modified environments, such as this Mediterranean-Pyrenean borderland, nature and culture cannot be meaningfully studied apart. Consequently issues of land degradation must be situated within the broader context of socio-natural interaction. Such a study cannot be approached solely from a natural or social science perspective; what is required, and what has been developed in this research, is a transdisciplinary methodology whereby natural phenomena are situated within their historical and socio-cultural context. Central to that context is the need to position the system within a long term evolutionary dynamic, thus allowing us to view the system in process, rather than as a synchronic present day snapshot. Within this 'longue duree' temporal and spatial scales are seen to be critical. It is argued that land degradation is at root a perceptual issue, thus perception and cognition are seen as critically important in this study. The core field work acts to expose both the physical and social identities of the Aspre, and the multiple perceptions of land degradation held by its inhabitants. The research identifies a series of 'perceptual filters' through which the environment of the Aspre is experienced, and by means of which meaning is negotiated. The recognition of the multiple environmental perceptions and plural rationalities is of crucial importance when contemplating the possible future pathways open to the Aspre, with respect to sustainable futures. What emerges from this research is a redefinition of land degradation in the Aspre, from that of a purely physical issue, to the realization that what we are dealing with are changing social identities within changing landscapes.