Browsing by Author "Ellis, Freddie"

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    Die gronde van die Karoo
    (Stellenbosch : Stellenbosch University, 1988) Ellis, Freddie; Lambrechts, J. J. N.; Stellenbosch University. Faculty of AgriSciences. Department of Soil Science.
    ENGLISH ABSTRACT: Soil information pertaining to one of the most extensive arid and semi-arid areas of South Africa is limited. This area, known as the Karoo, comprises 36 million hectares or 32% of the surface area of South Africa. The purpose of this study was to gather as much information as was possible regarding the distribution, morphology, classification, physical, chemical and fertility status of the soils of this area. The pedosystem concept was used to identify and demarcate the terrain and soils of this study area. This assumes that a fair degree of interdependence exists between the environmental characteristics, terrain morphology and the soil. From this a general map (scale 1: 1 000 000) of the Karoo was produced. This illustrates broad soil patterns, while topsoil texture classes and underlying materials can easily be read from the map. In addition, terrain characteristics (i.e. percentage level land and relief) are also given. For the interpretation of soil and terrain characteristics it was necessary to define a small number of natural regions of the Karoo. In these regions the natural resources of soil, terrain and climate are strongly interdependent. They have been called broad physiographical regions. Twenty such regions have been identified in the Karoo. For each broad physiographical region a description is given of the nature and extent of the terrain together with the distribution of the soils with their morphology, classification, physical and chemical characteristics and fertility status. The soils of the Karoo can conveniently be arranged into seventeen broad soil patterns. It was clear that shallow calcareous lithosols and red apedal soils with a high base saturation occupy the largest area of the Karoo. The red soils usually have sandy topsoils (A horizon) while the clay content of the calcareous lithosols is slightly higher varying from 6- 15%. The deep, weakly structured soils which are associated with unconsolidated deposits and which should have a high potential for irrigation, occupy ca. 1 million hectares and occur mostly in the central , northern and eastern parts of the Karoo. Approximately 22 million hectares (60%) of the soils of the Karoo are stony and a further 14% are covered by desert pavement.
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    Petroduric and "petrosepiolitic" horizons in soils of Namaqualand, South Africa
    (Universia, 2012) Francis, Michele Louise; Fey, Martin V.; Ellis, Freddie; Poch, Rosa Maria
    Indurated, light-coloured 'sepiocrete' horizons have been found in Namaqualand Calcisols and Durisols. These horizons resembled calcrete but were non- to only mildly calcareous, resisted slaking in acid and alkali, and often broke with a conchoidal fracture. The presence of elevated quantities of sepiolite in the bulk-soil was confirmed by XRD analysis. The degree of induration in some these horizons suggested cementation by silica, and so in this paper the slaking properties, bulk chemistry, mineralogy and micromorphology of these horizons are compared with the typical silica-cemented, reddish-brown petroduric/duripan (dorbank) encountered in the region. 'Sepiocrete' horizons are chemically, mineralogically and morphologically distinct from the petrocalcic and petroduric horizons with which they are commonly associated. Micromorphology of the petroduric horizons revealed prominent illuviation in the form of oriented clay parallel to grains and crescent coatings on voids, a red matrix due to iron oxides, and translucent, isotropic amorphous silica coatings on grains and voids. In the 'sepiocrete' horizons, sepiolite appeared as a matrix of interlocking, sub-parallel fibres while the amorphous material was localised. The amorphous material was silica-rich with prominent aluminium and lesser magnesium; light brown under plane polarised light; not completely isotropic and had a lower birefringence than the sepiolite. The calcite was usually micritic, but also appeared as loose granules and as elongate crystals in a sepiolite matrix. The presence of the laminar Si-Al -rich areas on the sections suggested at the least localised duric properties and so mutual reinforcement of sepiolite and silica is possible. However, the 'sepiocrete' horizons did not meet the slaking requirements of the petroduric (dorbank) horizons and are distinct in appearance to the typical petroduric horizons in the region. They contained more MgO than the region’s typical petroduric, and too little SiO2 to be silcrete. While the '-crete' terminology provides a useful expression of the cemented nature of the horizon, in order to fit existing soil classification and description schemes the terms 'sepiolitic' and 'petrosepiolitic' (in the same sense as 'calcic' and 'petrocalcic') are proposed and defined. The term 'sepiolitic' would be useful in the adjectival form in petrocalcic or petroduric horizons where sepiolite is significant but not the primary cement. The genesis of the 'petrosepiolitic' horizons is likely to be essentially similar to that of petrocalcic and petroduric horizons, except for chemical differences in the matrix solutions from which secondary minerals were precipitated, dictated by the pH and evaporative evolution of the soil solution.