Doctoral Degrees (Conservation Ecology and Entomology)

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Browsing Doctoral Degrees (Conservation Ecology and Entomology) by Subject "Agriculture -- Economic aspects -- South Africa"

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    Characterisation of soil macro- and mesofauna diversity and their contribution to soil health in grain agroecosystems
    (Stellenbosch : Stellenbosch University, 2023-03) Mamabolo, Emogine; Pryke, James S. ; Gaigher, Rene; Stellenbosch University. Faculty of Agrisciences. Dept. of Conservation Ecology and Entomology.
    ENGLISH ABSTRACT: Agriculture is the most important source of food and critical to the South African economy, yet it is detrimental to the environment, including the soil. We need to find innovative ways to achieve agricultural sustainability. Sustainable models are increasingly being adopted, but the major challenge remains measuring their effectiveness. Soils are inextricably linked to sustainable agriculture, as good soils promote crop growth and yields, while sensitive to chemical inputs that farmers place on the croplands. Due to the importance and sensitivity of soil, the assessment of soil health and soil fauna biodiversity has been proposed as an indicator of sustainability yet rarely considered when making recommendation for sustainable agricultural intensification. This dissertation explores the differences in diversity of soil macro-and mesofauna (from here on called soil fauna) under different agricultural land uses, namely conventional, conservation, integrated and natural grasslands, and how this affects the soil physicochemical environment and decomposition processes. The status of macrofauna as bioindicators of soil health was explored to provide a more direct tool in measuring soil function and sustainability. Biodiversity metrics revealed that cultivation under minimum soil disturbance coupled with complex vegetation and soil cover benefited soil fauna and allowed the establishment of most functional groups, which are crucial for pest control, nutrient cycling, and decomposition. Therefore, reduced tillage and increased structural complexity are recommended for preserving soil arthropod diversity and associated ecosystem services. Litter decomposition was positively linked to soil fauna species richness and not abundance or diversity. Results also showed that, soil fauna significantly contributed to decomposition, but contributions are highly depended on temperature, soil moisture and land use intensity. These findings highlight the importance in understanding management effects on soil fauna functional roles in maintaining nutrient cycling and soil health. Soil characterisation showed that conventional land uses favoured some important soil properties, however the overall effects of the soil physicochemical environment on fauna were complex, implying that sustainable intensification will not only be beneficial for productivity but also for the promotion of soil fauna and ecosystem services. Multivariate analyses of soil health characterisation allowed for the development of a simple but robust soil health assessment tool using soil macrofauna as indicators. The tool is important for assessing land use management and associated effects on soil health and ecosystem function. Overall, this dissertation shows that sustainable management, increased biodiversity, and increased soil health complement each other. Compared to their conventional counterparts, the conservation and livestock integrated land uses optimised favourable and stable conditions for various soil fauna groups and were more like that of the natural grasslands. As some of the important soil variables are favoured by more intensive land uses, designing sustainable and functional schemes is a lengthy process which requires patience, as soil itself is an ever-evolving entity which needs time to generate and/or restore. Here it is shown that low intensity agriculture promotes health soil fauna, thus sustainable management of soils in agriculture has the potential to increase the overall soil health, biodiversity, and function, meaning they (ecosystem engineers) can restore degraded soils and ecosystem services.