Owing to the crippling nature of arthritis, surgeons have been trying for well over a century to successfully treat this debilitating disease particularly when attacking the hip joint. In the early 1970s, Sir John Charnley started with total hip replacement as a solution to this ever-increasing problem. Many different designs were developed but all the designs revolved around a femoral stem, femoral head and acetabular component. Independent of the design, longevity of the implant remains a problem. The major cause of replacements, according to various hip registers, is due to aseptic loosening resulting from osteolysis. According to these registers, the average in-vivo life of a hip replacement is approximately 12 years. The main aim of this study was to determine the root cause of mechanical failure of the acetabular cups and to determine the origin of the excessive amount of ultra-high molecular weight polyethylene (UHMWPE) wear debris floating in the joint resulting in osteolysis. During the study, various techniques were used to investigate the acetabular components to try to establish the root cause of mechanical failure. These techniques included: 1. Visual inspection 2. Investigation making use of dye penetrant spray 3. Investigation under stereo microscope 4. Investigation making use of a scanning electron microscope 5. Electrophoresis 6. Mass-spectrometric analysis 7. Analysis of the synovial fluid on high-frequency linear-oscillation machine (SRV). The wear debris retrieved from the scar tissue surrounding the joints of a number of patients was also analysed. Apart from the obvious defects such as mechanical damage due to impingement, the main defect on which this study focuses is the wear patches found on the inside of the acetabular components. The wear areas were presented as areas where the surface layer of the UHMWPE was ripped off by adhering to the rotating femoral head. This type of failure is possible if localised overheating takes place resulting in the material either adhering to the rotating femoral head or the material being squeezed out under the prevailing pressure. Both these mechanisms were confirmed by the wear debris retrieved from the scar tissue, being either droplets of UHMWPE or whisker-like wear products. To confirm the existence of elevated temperatures the brown discolouring on the inside of the acetabular cups was analysed, making use of electrophoresis, mass-spectrometric analysis and scanning electron microscope recordings. In this part of the study, it was confirmed that localised temperatures on the bearing surface had reached at least 60°C during in-vivo service. This temperature was confirmed by inserting a thermocouple just under the surface of an acetabular cup and then measuring the temperature while in-vitro testing was taking place on a hip simulator. The wear debris as retrieved was also duplicated in laboratory experiments while the temperature on the surface of an acetabular cup was monitored. It was established that wear particles similar in shape and size were formed at temperatures in excess of 90°C. At temperatures above 50°C the UHMWPE had visually shown extensive increase in creep, indicating that at these temperatures the material softens sufficiently for this type of debris to be generated The overheating as described can also only occur if there is a lack of lubrication in the bearing couple. The synovial fluid from 12 patients was retrieved during revision surgery. This synovial fluid was then tested on a high-frequency linear-oscillation machine (Optimol SRV test machine) to determine the lubricity characteristics of the synovial fluid as retrieved. It was discovered that the load-carrying capability of the synovial fluid did not comply with the minimum requirements for a fluid to function as a lubricant. The final conclusion of this study is that excessive amounts of wear debris are generated due to the localised overheating of the bearing couple as a result of insufficient lubrication. The localised heat build-up results in excessive amounts of wear debris being generated and deposited in the joint area resulting in osteolysis. / Thesis (PhD (Mechanical Engineering))--University of Pretoria, 2005. / Mechanical and Aeronautical Engineering / unrestricted

A field trial was established in January 2002 under a centre pivot at Syferfontein (Sasol) open cast mine, close to Secunda in the Mpumalanga Province (Republic of South Africa). Field measurements of crop, soil, water and weather were taken up till May 2003. Growth analyses were undertaken during the growing period of the planted pastures. Crop growth parameters and input parameters for long term predictions with the SWB model were also determined. The determinations were made for five planted pastures to evaluate if they could be irrigated with Na2SO4 rich mine effluent, and to see if the SWB model could reliably simulate crop growth, as well as the salt and water balance. The results indicated that Fescue (cv. Iewag), Lucerne, and Fescue (cv. Demeter) could be grown successfully with satisfactory yield and quality. No leaf burn was observed for the irrigated pastures. The ECe, pH and ESP of the soil increased slightly over the irrigation period, whereas the EC, pH and SAR of the soil solution fluctuated with rainfall. The model predicted the leaf area index (LAI), top dry matter (TDM), soil water deficit and salts reasonably well. In the long-term, 1420 mm year -1 of mine effluent can be used through irrigation. 93% of the salt added through irrigation was predicted to leach from the profile in a 20 year irrigation period which the rest precipitating in the 0.8 m deep soil profile in the form of gypsum. The Na2SO4 mine water can be utilized for pasture production provided that proper irrigation management and fertilization is done. Copyright 2004, University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. Please cite as follows: Beletse, YG 2004, Modelling the soil water and salt balance of planted pastures irrigated with sodium sulphate rich mine effluent, MSc(Agric) dissertation, University of Pretoria, Pretoria, viewed yymmdd < http://upetd.up.ac.za/thesis/available/etd-01182005-083427 / > / Dissertation (MSc (Agric))--University of Pretoria, 2006. / Plant Production and Soil Science / unrestricted

This study concerns the phylogeography of Sandelia capensis and S. bainsii (family Anabantidae), two freshwater fish species endemic to Cape coastal rivers of South Africa. The mitochondrial DNA (mtDNA) cytochrome b gene (S. capensis) and control region (S. capensis and S. bainsii) were used as genetic markers. Sandelia capensis has a wide distribution, and occurs in most river systems of the Cape Floristic Region (CFR). Therefore, by studying the genetic variation within the species we could investigate the drainage history of this region. Two major historically isolated lineages were identified within this species, one comprising west coast populations and the other south coast populations. Genetically unique lineages were also identified within each of these two major clades. The split between the two major clades dated back to the Pliocene, while divergence times for lineages within them dated back to the Pleistocene. River capture events and sea level changes in the CFR played a major role in shaping the genetic variation that we observe within S. capensis today. Sandelia bainsii is restricted to a few Eastern Cape coastal rivers, and is classified as endangered. Within this species two divergent clades were identified, a Great Fish/Kowie lineage and a Buffalo/Gulu lineage. Sandelia capensis is also of conservation importance since certain populations are declining as a result of many different threats. In identifying these genetically unique lineages, certain areas (rivers/populations) could be prioritized for conservation management. The two major lineages identified within each of the two species should be conserved as separate units and not be intermixed. Two genetically very unique populations identified within S. capensis, the Heuningnes and Diep, are under severe pressure and should also be prioritized for management. In addition, a preliminary phylogenetic study was performed on the Anabantidae using mtDNA 16S rRNA sequences. This was done to investigate the phylogenetic relationships between the two Sandelia species (classified as sister taxa) and also their relationships with the other anabantids. The phylogenetic relationships between the anabantids were largely unresolved, probably due to an ancient radiation. / Dissertation (MSc (Genetics))--University of Pretoria, 2006. / Genetics / unrestricted

This study assesses the performance of an atmospheric GCM forced with persisted SSTs in simulating austral summer precipitation at smaller spatial (regional) scales. Two statistical recalibration techniques of differing technical complexity are then presented and compared to get an idea as to which method among them is best suitable for southern Africa. The two regression-based methods applied in recalibrating the ECHAM4.5 GCM output during austral summer in southern Africa are based on model output statistics (MOS) using principal components regression (PCR) and canonical correlation analysis (CCA) to statistically link archived records of the GCM to regional rainfall over much of Africa south of the equator. A linear statistical model linking near-global sea-surface temperatures (SSTs) to regional rainfall is also developed. Southern Africa is divided into 18 homogeneous regions using cluster analysis. The potential predictive skill of summer precipitation over each region from raw-GCM ensembles, the linear statistical and MOS models is evaluated using the relative operating characteristics (ROC) score and the ranked probability skill score computed over a 12-year retroactive period 1989/90–2000/01. The MOS technique outperforms the raw GCM ensembles and the linear statistical model in certain cases. On many occasions, the PCR-MOS performs better than CCA-MOS but the former does not show clear superiority over the latter method because the two methods are in a broad sense performing the same task. The need to recalibrate GCM predictions at regional scales to improve their skill at smaller spatial scales is demonstrated in this study. / Dissertation (MSc (Meteorology))--University of Pretoria, 2007. / Geography, Geoinformatics and Meteorology / unrestricted

Shoot growth and leaf photosynthesis of 6-7 year-old, field-grown mango (Mangifera indica L. cv ‘Kent’) trees subjected to the following irrigation regimes were monitored during the season of 2002/2003: Co, control (±95% of field capacity, FC); DI-1 and DI-2, continuous deficit irrigation (±79% and ±69% of FC, respectively); RDI, regulated deficit irrigation (like Co except that irrigation water was withheld for 2 weeks in Dec 2002/Jan 2003 during the final stage of fruit growth); and Co-F, farm control, full irrigation when soil moisture was lower than -10 KPa). During the post-harvest flushes in 2002 and 2003, Co-F shoots showed 56% more shoot volume and dry mass than Co indicating that a large amount of irrigated water was used for such vigorous growth. There were no significant differences in the number of flowering canes between all irrigation treatments during the flowering flush in 2002. However, the pattern of decreasing numbers of flushing terminals and shoot numbers was concurrent with decreasing amounts of irrigation water applied (Co-F>Co>RDI>DI-1>DI-2). The results indicated that part of the irrigation water applied to Co-F was used for vigorous vegetative growth; while in the DI-2 treatment severe shoot growth reduction seemed to seriously hinder productivity. Midday leaf assimilations in well-irrigated ‘Kent’ mango trees in the field during winter and spring amounted to (4.5 ± 0.6 and 5.9 ± 0.3 µmol CO2 m-2 s-1, respectively) and were lower than in autumn and summer (6.4 ± 1.8 and 11.1 ± 0.8 µmol CO2 m-2 s-1, respectively). Differences in mean photosynthetic (Pn) rates between the three field-grown and well-irrigated cultivars, ‘Kent’, ‘Keitt’ and ‘Heidi’, were not significant except for January and April 2003. Young leaves (<25 DABB, days after bud break) photosynthesized only to a small extent in winter and summer at midday (0.2 ± 0.9 and 0.4 ± 0.3 µmol CO2 m-2 s-1, respectively). However, high Pn rates at midday were reached in leaves aged 90-180 DABB in summer (10.3 ± 2.0 µmol CO2 m-2 s-1) and maintained at leaves that were older than 365 DABB (10.4 ± 0.7 µmol CO2 m-2 s-1), while those in winter were lower for both leaf age groups (3.2 ± 0.6 and 3.5 ± 0.8 µmol CO2 m-2 s-1, respectively). In field-grown ‘Kent’ mango trees, water deficit reduced significantly the photosynthetic capacity in the irrigation treatment DI-2 across the entire year, especially during late spring and early summer, in comparison to the Co-F treatment, while differences between the treatments Co, DI-1, and RDI were negligible (in the range of 7.0-7.3 µmol CO2 m-2 s-1) across the entire year. Generally, the Co-F treatment maintained slightly higher photosynthetic rates (7.9 ± 3.2 µmol CO2 m-2 s-1) over the entire year than the other treatments showing that they received more water. Nevertheless, DI-2 maintained reasonable rates (6.5 ± 1.7 µmol CO2 m-2 s-1), even though they were severely stressed indicating that those trees apparently adapted to low water regimes by increasing their water use efficiency. / Dissertation (MInst Agrar (Horticulture))--University of Pretoria, 2006. / Plant Production and Soil Science / unrestricted

The pupal cocoons of two southern African wild silkmoth species, Gonometa postica and G. rufobrunnea (Lepidoptera: Lasiocampidae), are composed of high quality silk and have potential as a commercially viable resource. However, limited ecological research has been done on these species, and their population dynamics is especially poorly known. A steady and predictable supply of cocoons is paramount to the economic sustainability of a wild silk industry. There is thus an urgent need for documenting and understanding the population dynamics of southern Africa’s Gonometa species. Here, the temporal and spatial variation of pupal (and thus cocoon) abundance, as well as associated natural enemies, are described for both Gonometa species for the first time. The larval parasitoid species emerging from parasitised pupae were quantitatively associated with species-specific emergence holes, making field-identification of these species possible. Eleven sites in total were sampled, over four generations, across the region where both species have historically reached high population densities. Apparent spatial synchrony in pupal abundance found between sites suggests that climate is responsible for observed population size fluctuations. As predicted from their life history traits, temporal variability was lower than expected for classically eruptive species. Gonometa species thus have an intermediate position on the population dynamics gradient. In turn, the responses of natural enemies were not predictable from Gonometa species defensive traits, but appear to be mediated by between-species cocoon strength differences. Using data on the number of G. postica pupae per tree and associated parasitism at several sites, the importance of the degree of spatial explicitness in the quantification of aggregation and the detection of density dependence was illustrated. The spatially explicit method gave different results and more information regarding the spatial pattern of pupal abundance and parasitism than non- and semi-explicit methods. Similarly, the detection of density dependence in parasitism rates was affected by the use of spatially explicit data, with the spatial explicit approach giving different and more biologically informative results than traditional, non-spatially explicit methods. This has marked implications for previous insect-host - parasitoid studies aimed at detecting density dependence. The variability in cocoon size, a surrogate for larval performance, adult fecundity and silk yield, revealed that gender, followed by species, contributed most to observed size differences, with no clear differences between generations or localities. Finally, the between-host plant and withinhost plant distribution ofG. postica and G. rufobrunnea pupae was quantified, chiefly investigating the deterministic nature of the choice of pupation site. The distribution of both species at these scales was found to be markedly non-random, with pupae generally preferring specific tree characteristics and micro-sites. These results now provide the basis for recommending an appropriate utilisation strategy for southern Africa’s wild silk moths. Based on the spatial and temporal variability in pupal abundance observed, a constant and predictable cocoon supply for natural harvesting is unlikely. Long-term, broad-scale documentation of Gonometa species population cycles may make it possible to predict cocoon availability in the future. Until such research is done, it is recommended that the current practise of only collecting cocoons from which moths have emerged be continued. Simultaneously, artificial rearing and seeding as alternative utilisation strategies should be experimentally explored based on the information gathered and patterns identified here. / Thesis (DPhil (Entomology))--University of Pretoria, 2007. / Zoology and Entomology / unrestricted

Objective of Research The interest in crop modelling started since the introduction and popularisation of computer technology, which facilitated the dynamic simulation of complex natural systems. In particular, crop growth and soil water balance models for irrigation scheduling are popular at locations where water is a limiting factor for crop production. In a Water Research Commission project, the soil water balance model (SWB) for irrigation scheduling under full and deficit irrigation was made available. The SWB model is a relatively simple generic crop growth model based on sound physical and physiological principles, (i.e. mechanistic) using daily climatic inputs for daily time-step calculations of the soil-plant-atmosphere water balance to estimate plant growth water use. The SWB model was primarily developed for predicting real-time soil water deficit of field crops with a one-dimensional canopy light interception and water redistribution procedure. Hedgerow tree crops are planted in widely spaced rows to allow access between trees to carry out necessary management practices (e.g. pest control and harvesting). Distribution of energy is not uniform in widely spaced crops. In addition, localised under tree irrigation is often used for tree crops to reduce system installation costs. This irrigation (micro- or drip) only wets a limited area under the canopy of the trees so that evaporation from the soil surface is also not uniform. One can expect root density to vary with depth as well as with distance between the rows so water uptake for transpiration will also vary in two dimensions. It is also essential to take into account the limited volume of soil wetted under micro-irrigation. If this is not done, the soil capacity will be incorrectly estimated with a standard one-dimensional approach, leading to undesirable over-irrigation in the wetted zone, as well as possible crop stress resulting from a too long an irrigation interval. In order to accurately estimate canopy growth, water balance and yield, it is therefore essential to model canopy radiant interception and soil water balance of hedgerow tree crops in two dimensions and on an hourly time step, based on sound physical principles. Lack of suitable user-friendly tools to mechanistically describe the two-dimensional energy and soil water balance of tree crops was identified. Due to the importance of fruit crops, on the export as well as local markets, as well as the encouraging results from the initial SWB model, it was decided to improve the SWB model by incorporating a two-dimensional system for use in hedgerow plantings. This thesis reports on the methodology developed to monitor the energy and soil moisture differences within various hedgerows through 24 hour cycles and the results obtained, as well as the subsequent use of the results to evaluate the 2-dimensional water balance model. This research was an integral, but independent, part of a larger research thrust, i.e. the development of a two-dimensional fruit tree water balance model that can account for the unique fractional interception of solar radiation associated with hedgerow orchards as opposed to the horizontal planar interception encountered in agronomic crops. The primary objective of this thesis is not the actual programming and mathematical manipulations of the relevant algorithms but to create a reliable data base and then evaluate the model. The primary objective of this thesis was to evaluate the model for deciduous fruit trees using peaches as an example and evaluate the model for evergreen fruit trees using citrus as an example. Model description In the overall research thrust two types of model, both predicting crop water requirements on a daily time step, were developed for hedgerow tree crops and included in SWB: i) A mechanistic two-dimensional energy interception and finite difference, Richards’ equation based soil water balance model; and ii) An FAO-based crop factor model, with a quasi-2D cascading soil water balance model. For the sake of clarity and completeness, the principles of the models are presented in the thesis and are briefly described in this subsection. The first model calculates the two-dimensional energy interception for hedgerow fruit trees, based on solar and row orientation, tree size and shape, as well as leaf area density. The two-dimensional soil water redistribution is calculated with a finite difference solution. The two-dimensional energy interception model assumes leaves to be uniformly distributed within an ellipsoid truncated at its base, and radiation penetrating the canopy is attenuated according to Beer’s law. This geometry is very versatile as many different shapes can be generated. In order to determine the spatial distribution of soil irradiance across the tree row, the canopy path length through which the radiation must travel to reach a certain point on the soil surface is calculated. Radiation can penetrate neighbouring rows, so two rows on either side of the simulated row are considered. Beam or direct radiation and diffuse radiation for the PAR (photosynthetically active radiation) and NIR (near-infrared radiation) wavebands are calculated separately, as they interact differently with the canopy. The ratio of actual measured to potential radiation is used to estimate the proportion of direct and diffuse radiation in these two spectral bands. The attenuation of beam radiation by the canopy is strongly dependent on zenith angle, and, for crops planted in rows, azimuth angle and row orientation will also be crucial. Elevation and azimuth angles are calculated from latitude, solar declination that depends on day of year, and time of day. Before the length of canopy through which radiation penetrates can be calculated, azimuth angle needs to be adjusted to take row orientation into account. Input data required to run the two-dimensional canopy interception model are: day of year (DOY), latitude, standard meridian, longitude, daily solar radiation, row width and orientation, canopy height and width, bare stem height and distance from the ground to the bottom of the canopy, extinction coefficient, absorptivity and leaf area density. In order to simulate two-dimensional water movement in the soil, a grid of nodes were established. This divides the soil up into a number of elements. The distances between nodes are selected so that model output can easily be compared to field measured values. Each element has its own physical properties, so this scheme allows variation in soil properties in two dimensions. Symmetry planes are assumed to occur mid-way between two rows on either side of the hedgerow and no water flux is allowed across these planes. The model redistributes water in the soil in two-dimensions using a finite difference solution to Richards’ continuity equation for water flow. The aim is to find the matric potentials, which will cause the mass balance error to be negligible. This is done using the Newton-Raphson procedure. Two lower boundary conditions can be chosen in the model: i) gravity drainage for well-drained soils, and ii) zero-flux lower boundary to simulate an impermeable layer. A precipitation or irrigation in mm is converted to a flux in kg m-1 s-1 by dividing the time step and multiplying by the horizontal distance over which the water is distributed. The infiltration does not have to be uniform over the surface. Non-uniform infiltration is especially important in very coarse soils where lateral redistribution is likely to be limited, or in the case of micro-irrigation. As with the infiltration flux, evaporation is multiplied by the horizontal distance over which it occurs in order to get an evaporative flux in kg m-1 s-1. Potential vapotranspiration (PET) is calculated from weather data using the Penman-Monteith equation and the maximum crop factor after rainfall occurs. PET is then partitioned at the soil surface into potential evaporation and potential transpiration depending on solar orientation, row direction and canopy size, shape and leaf area density. Crop water uptake (transpiration) can either be limited by atmospheric demand or soil-root water supply. Root densities at different soil depths are accounted for in the calculation of root water uptake. The user can specify root depth and the fraction of roots in the wetted volume of soil. Required inputs for the two-dimensional soil water balance model are: starting and planting dates, altitude, rainfall and irrigation water amounts, as well as maximum and minimum daily temperature. Two points on the water retention function (usually field capacity and permanent wilting point), initial volumetric soil water content and bulk density are required for each soil layer. Soil saturated hydraulic conductivity can also be entered as input for each soil layer, or calculated by the model using the water retention curve. Row distance, wetted diameter of micro-jets or drippers, fraction of roots in the wetted volume of soil as well as distance of the nodes from the tree row are also required as input. The second, simpler model, based on the FAO crop factor approach, was developed to enable users to predict crop water requirements with limited input data. This model includes a semi-empirical approach for partitioning of aboveground energy, a cascading soil water redistribution that separates the wetted and non-wetted portion of the ground, as well as prediction of crop yields. The FAO-based crop factor procedure was combined with the mechanistic SWB model, thereby still allowing evaporation and transpiration to be modelled separately as supply and demand limited processes. The crop factor model does not grow the canopy mechanistically and therefore the effect of water stress on canopy size is not simulated. The simpler crop factor model should, however, still perform satisfactorily if the estimated canopy cover closely resembles that found in the field. The following input parameters are required to run the FAO-type crop factor model: planting date, latitude, altitude, maximum and minimum daily air temperatures, FAO crop factors and duration of crop stages. The input data required to run the two-dimensional cascading model are rainfall and irrigation amounts, volumetric soil water content at field capacity and permanent wilting point, as well as initial volumetric soil water content for each soil layer. Row spacing, wetted diameter, distance between micro-irrigators or drippers and the fraction of roots in the wetted volume of soil are also required. Required input data for yield prediction with the FAO model are FAO stress factors for growing stages and potential yield. Field Trial Evaluation of the model was carried out for a wide range of conditions (row orientation, period of the year and canopy density). For this purpose, two field trials were set up. The first trial was established in a peach (Prunus persica cv Transvaalia) orchard on the lysimeter facilities at Hatfield (Pretoria University experimental farm). This provided a site where detailed observations could be easily recorded to evaluate the SWB model for deciduous trees. The second trial was established in a citrus clementine (Citrus reticulate cv. Nules Clementine) orchard at the Syferkuil experimental farm of the University of the North. This was the site where measured data were collected to evaluate the SWB model for evergreen trees. In both field trials, the following field measurements were carried out and used to evaluate the two-dimensional energy interception and soil water balance model: i) Weather measurements (temperature and relative humidity, wind speed, solar radiation and rainfall). ii) Soil texture, bulk density, penetrometer resistance. iii) Volumetric soil water content with neutron water meter and time domain reflectometry (TDR). iv) Soil matrix potential with heat dissipation sensors. v) Root distribution by taking soil core samples and washing out roots to determine root length. vi) Soil irradiance at different distances from the tree row with tube solarimeters. v) Leaf area index and density with a LAI-2000 plant canopy analyser. vi) Canopy size and row orientation. In addition, load cell lysimeters were used in the peach orchard at Hatfield in order to measure crop water use. An additional field trial was carried out at the Hatfield experimental station on Leuceaena (Leucaena leucocephela) trees in order to test the two-dimensional radiant interception model for different environmental conditions (tree size and shape as well as row orientation). For the same purpose, two other trials were carried out on two commercial orchards at Brits in Empress Mandarin (Citrus reticulate cv. Empress) and Delta Valencia (Citrus sinensis [L.] cv. Osbeck) orchards. In these field trials, weather data were recorded, soil irradiance across the row was measured with tube solarimeters, as well as leaf area index and density, canopy size and row orientation. Results The simple, quasi two-dimensional, cascading soil water balance model was calibrated using data from the peach trial at the Hatfield experimental station. In the process, FAO basal crop coefficients (Kcb) were determined for first and second leaf peach trees. The daily crop factor (Kc) was calculated using evapotranspiration measurements from the lysimeters and the grass reference evapotranspiration calculated from weather data. The Kcb values for the various growth stages were determined by fitting an appropriate line through the lower values of Kc, which were taken to reflect the condition where the soil surface was dry (negligible evaporation), subsoil drainage was negligible and there was sufficient water not to restrict transpiration. There was good agreement between predicted and measured daily soil water deficit for water stressed and non-stressed treatments. This was expected since the calibration data came from the trial. Field measurements in Hatfield also indicated that in hedgerow plantings the whole area across the row must be borne in mind when assessing soil water content. The practice of using single or restricted locality measurements, as utilised in agronomic crops, can be misleading in orchards. The reason for this is the effect of the irrigation distribution and rain interception by the canopy, the variation in radiation interception by the canopy across the row, the irradiance reaching the soil surface as the season progresses, the presence of a grass sod or bare soil in the inter-row region and the root density across the row. In both field trials at Hatfield and Syferkuil, it was found that there are significant amounts of roots in the inter-row region and thus this portion of the rooting volume must not be disregarded when assessing the water balance. The two-dimensional energy interception and soil evaporation components were evaluated separately. The crucial interactions between the model components were integrated in the validation of the two-dimensional soil water balance model, which uses the energy interception and soil evaporation sub-models to split evaporation and transpiration. The radiant interception model predictions and the tube solarimeter measured soil irradiance generally gave very good agreement at different distances from the tree row and in different orchards. However, some discrepancies between measurements and model predictions occurred. This was attributed to the presence of trunks and branches shading the tube solarimeters at low leaf area densities, irregularities in the shape of the hedgerow, and nonuniform distribution of leaves within the canopy. In one case the canopy shape differed drastically from that used in the model. The output obtained with the two-dimensional soil water balance model was compared to independent field measurements in order to evaluate the full SWB two-dimensional model. Volumetric soil water content data collected with the TDR system in the peach and citrus orchards were compared to SWB simulations. Results of model simulations done during drying cycles showed that the surface layer predictions were generally very good. However, in certain situations discrepancies between measurements and simulations were observed, in particular, for deeper soil layers. This could have been due to spatial variability of soil properties, as well as soil disturbance during the installation of TDR probes. It is clear that TDR probes can be used in irrigation scheduling to determine crop water use over certain periods. Caution should, however, be exercised in the interpretation of absolute values of volumetric soil water content obtained from the probes. Scenario modelling and sensitivity analyses were carried out by varying some input parameters and observing variations in certain output variables. The aim was to show an application of this tool to identify the most suitable management practice in order to maximise water use efficiency. Two case studies were considered for two “virtual” orchards located at different latitudes and in different climates (Kakamas in the Northern Cape and Stellenbosch in the Western Cape). The results of the scenario simulations indicated that, based on the inputs used, the orchards should be planted in a N-S row orientation, a wetted diameter of 0.5 m should be applied when the canopy width is 2 m, in order to minimize water losses through evaporation. As the canopy width increased to 3 m, so the wetted diameter should be increased to 1.5 m. If the wetted diameter is too small, transpiration and thus yield will be reduced. A sensitivity analysis was also carried out for both case studies varying the fraction of roots in the wetted volume of soil, and observing variations in the output results of evaporation and transpiration. The contribution to crop water uptake from the inter-row volume of soil can be high, in particular under high atmospheric evaporative demand, and this needs to be accounted for in irrigation management in order to maximise rainfall use efficiency in areas of higher summer rainfall. Conclusions and recommendations The methodologies developed to measure the temporal and spatial variation in solar radiation and thus the energy distribution within Hedgerow orchards worked well. The methods used to measure the temporal and spatial variation of the soil water balance also worked well. Thus a very good data set was generated that enabled the sound evaluation of the 2-D SWB model. Thus one can conclude that the two-dimensional energy interception and soil water balance model that was developed in the overall research thrust and included in the Soil Water Balance irrigation scheduling model worked well. The simpler model, based on the FAO crop factor approach and a cascading soil water balance, that was also developed to enable users to predict crop water requirements with a limited set of input data, also gave very satisfactory results. The FAO-based model and the cascading soil water balance were calibrated for first leaf and second leaf peaches at Hatfield. The two-dimensional model was fully evaluated for deciduous orchards using data obtained in field trials on peaches and Leucaena (Hatfield). For model validation in evergreen citrus orchards, data obtained in field trials set up at the Syferkuil experimental station (University of the North) and on two commercial farms in Brits were used. Irregular trunks and branches could cause inaccuracies in predictions of the energy balance. At low leaf area densities, the shade from trunks and branches is not accounted for in the SWB model. The relative importance of non-symmetric canopy shape as opposed to nonuniform leaf distribution did have an effect but indications where that this was not critical. The major difficulties encountered in the evaluation of the soil water balance were due to spatial variability of soil properties and disturbance of the soil when the water status monitoring sensors were installed. Careful installation is therefore recommended when using sensors that give localised measurements like those used in this study (heat dissipation sensors and TDR probes). The successful evaluation of the two-dimensional energy interception and soil water balance model opens the opportunity to develop a useful yield predictor and productivity efficiency measure if one knows the canopy to fruit ratio. This information could also be useful for fruit colour and internal quality research. As demonstrated with data from the peach trial at Hatfield, soil or cover crops between rows can also have a large effect on the efficient use of rainfall, and this could be further investigated. The biggest contribution of this model is likely to be the quantification of the contribution that rainfall can make to crop water use by taking the non-irrigated inter-row soil reservoir into account. It is recommended to accurately estimate the root fraction in the wetted and nonwetted volume of soil by digging a trench across the row, taking core soil samples and determining root densities. The two-dimensional energy interception and finite difference soil water balance model is expected to be more accurate than the cascading soil water balance, due to the sound physical principles on which it is based. The mechanistic detailed approach could give guidance with respect to the magnitude of errors made by using simpler, more empirical approaches. However, the two-dimensional model will also require more input parameters compared to the simpler cascading model. In particular, the most difficult parameters to determine will be the leaf area density for the radiation energy interception part due to the cost of the instrumentation, and the hydraulic conductivity for the soil part due to the specialised knowledge and scientific equipment required. On the other hand, the cascading model requires calibrated FAO crop factors in order to reasonably partition evaporation and transpiration. It would be interesting to compare the cascading and the two-dimensional soil water balance models against field measurements in order to determine the level of accuracy in predictions. The two-dimensional energy and soil water balance model is primarily meant to be a realtime, irrigation scheduling tool for commercial orchards. Results from this study should guide irrigation scheduling consultants, extension officers and farmers to more efficiently use scarce water resources on high value tree crops. The two-dimensional model, however, can also be used for planning purposes as demonstrated in the scenario simulations. The mechanistic canopy radiation interception routine which has been shown to be very accurate will make it possible to evaluate the effect of row orientation and spacing as well as the effect of wetted diameter and pruning practices on water use. This model also holds tremendous potential as a teaching aid to allow students to do “whatif?” scenario analyses and thus study cause and effect interactions of various orchard designs and practices. / Thesis (PhD (Agriculturae: Plant Production))--University of Pretoria, 2007. / Plant Production and Soil Science / unrestricted

No abstract available / Dissertation (MTh (Theology))--University of Pretoria, 2007. / Science of Religion and Missiology / unrestricted

Today's globalised team culture of business places a premium on effective social skill, as social skill is needed for effective leadership, customer services, negotiation as well as for the acquiring and sharing of information. Psychological tests are commonly used as aids in determining whether individuals have the necessary skills for a specific job. Practically all psychometric tests are western in origin, which implies that the measuring of the psychological constructs are based upon a western culture. This brings into question the bias and validity of psychometric instruments when utilised on other cultures, as constructs may not be similarly defined or interpreted in all cultural groups. Construct equivalence implies that the same construct is measured across all cultural groups being studied, regardless of whether or not the measurement of the construct is based on identical instruments across all cultures. Construct equivalence is thus a pre-requisite for valid comparison of scores across the cultural groups being studied. The aim of this study is therefore to determine the construct equivalence of the PIB/SpEEx Socialization Index for job applicants from diverse cultural backgrounds in the public safety and security sector in South Africa. Exploratory- as well as Confirmatory Factor Analytic techniques were used to determine the intercultural equivalence of the sociability and the A-sociability constructs underlying the PIB/SpEEx Socialisation Index. Preliminary single group Confirmatory Factor analysis was conducted to establish how good the data fit the model in respect of each of the cultural groups, followed by a multi-group analysis of factorial invariance. The results of this study revealed that the constructs of the PIB/SpEEx Socialisation Index are equivalent for the Black, Asian, White and Coloured groups. / Dissertation (MCom (Human Resources Management))--University of Pretoria, 2007. / Human Resource Management / unrestricted

Through the process of selection the measurement and prediction of behaviour has become an important activity in the field of psychology, especially in the workplace. A dynamic selection process can assist the organisation in identifying individuals who best suite it’s needs. Psychometric testing is the most common procedure in the prediction of human behaviour during selection. Seeing that not all instruments are valid and reliable, much controversy still exists on the use of such instruments in South Africa. Only by introducing instruments that apply to these criteria will psychometrics have a future in labour practices. The purpose of this study was to assess the construct validity of the First View™ , an instrument originating in the United States, for selection purposes in South Africa. By incorporating personality and cognitive ability into one instrument, First View™ , as a psychometric instrument, can be used in selection to determine job performance. The cognitive scale is based on Guilford’s Structure of Intellect and the personal scale on the Big Five Personality factors. The reliability and validity of this instrument have proved to be high in the United States. In order to investigate validity, First View™ had to be correlated with well established and valid South African instruments. In this study the Differential Aptitude test (DAT) and 16 Personality Factor Questionnaire SA-92 (16 PF) were used. The three tests were administered to a sample of 229 respondents from different race, gender, age and occupation groups, drawn by means of convenient sampling and random selection. Canonical correlation showed a strong relationship between the independent and dependant variables. From this a conclusion can be drawn that the 16 PF SA-92 and the personal scale of First View™ show a positive interrelationship. The multiple regression indicated a significant relationship between the predictors and the composite criteria, concluding that there is a strong relationship or overlapping between the DAT and cognitive scale of First View™. Thus, results indicate that First View™ can be a valuable instrument in selection. The findings and implications of the study are discussed and recommendations for future studies made. / Dissertation (MCom (Human Resources Management))--University of Pretoria, 2007. / Human Resource Management / unrestricted