Doctoral Degrees (Agricultural Engineering)

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The hydrological effects of fire in South African catchments.
(1994) Scott, David Findlay.; Schulze, Roland Edgar.
Stream-flow and storm-flow in four small catchments were analysed by the paired catchment method for a response to fire. Two of the catchments were vegetated with over-mature fynbos (the indigenous scrub vegetation of the south-western Cape Province, South Africa), one was afforested to Pinus radiata and the fourth to Eucalyptus fastigata. One of the fynbos catchments was burned in a prescribed fire in the late dry season. The other catchments burned in wildfires. Neither of the fynbos catchments showed a change in storm-flows. Annual total flow increases of around 16% were in line with predictions, being related to the reductions in transpiration and interception. The manner of stream-flow and storm-flow generation appeared to have remained unaltered despite the fire. The two timber plantation catchments experienced large and significant increases in stormflow and sediment yields, while total flow increased by 12% in the pine catchment and decreased marginally in the eucalypt catchment. After fire, storm hydrographs were higher and steeper though their duration was little changed. These fire effects are considered to be due to changes in storm-flow generation consistent with an increased delivery of overland flow to the stream channel. This was caused, in part, by reduced infiltration resulting from water repellency in the soils of the burned catchments. The inherent wettability of a wide range of soil types and textures from beneath timber plantations and other vegetation types over a broad geographic distribution in South Africa was measured by four methods. Soils with high repellency ratings, unrelated to fire, are common and are most likely to occur beneath plantations of Eucalyptus and Acacia spp. and indigenous forest. Water repellent soils played a role, at two of the three locations, in the generation of overland flow from small plots exposed to simulated rainfall. However, the inherent repellency of the dry soils was extreme, such that fire-induced water repellency was not a factor in the response of the plots. The important role of fire in this experiment was in burning-off of repellency in the surface layer of the soil and in removing ground cover.
Automated processor for optimizing tractor operation.
(1991) Lyne, Peter William Liversedge.; Meiring, Pierre Andre.
The agricultural tractor is designed as a general purpose machine and consequently, does not perform all its tasks at maximum efficiency. Various methods of increasing the field performance of these vehicles have been studied. Traction is one of the main factors limiting the field performance of the modern tractor. The process of developing traction has therefore been investigated by many researchers and although this study has resulted in a better understanding of the mechanics, it has not to any great extent assisted the operator to optimize performance in the field. It was concluded that in order to solve the problem the operator required a control system to maintain the dynamic load and inflation pressure at optimum levels. Work was carried out to develop and evaluate such a system using the Single Wheel Traction Research Vehicle at the USDA's National Soil Dynamics Laboratory in Auburn, Alabama, USA. A computer management system was developed to control the dynamic load, net traction and inflation pressure of the test tyre. During a simulated field operation the system was programmed to cycle the tyre over its operating range of dynamic load and inflation pressure while monitoring tractive efficiency. A tractive efficiency response surface was computed for the particular condition and the surface searched for the dynamic load and inflation pressure levels which resulted in maximum tractive efficiency. The tyre was then controlled and operated at maximum tractive efficiency. Evaluation showed that within the operating range of the tyre, tractive efficiency varied considerably with dynamic load, inflation pressure, net traction and soil condition. The results indicated that a considerable advantage could be obtained by using such an arrangement on a tractor. The system would automatically maximize the tractive efficiency of the tractor under the particular field conditions and with the particular implement being used. Implements could be ballasted and the hitch system used to control the weight transfer to ensure maximum tractive efficiency. Systems such as these would result in a significant improvement in the field performance of the machine and a reduction in management time required to optimize the performance of the tractor implement combination.
Combustion stress in compression-ignition engines.
(1989) Taylor, Andrew Bruce.; Meiring, Pierre Andre.
South Africa produces alternative fuels from a number of different sources. The properties of a fuel are known to affect the nature of combustion in compression-ignition engines significantly, and have occasionally resulted in engine failures. Combustion analyses have been conducted on a wide range of fuels and combustion has been thoroughly quantified. However, the role played by the different combustion variables in failures was not known. The result was that it was not possible to predict the implications of variations in the nature of combustion. There was thus a need to investigate the relative role of combustion variables in the failure of engines. The mechanisms of combustion and engine failure were studied. All the variables required to determine combustion and engine durability were measured simultaneously. This research required the development of a complete engine research facility as well as specialized transducers. Fast response surface thermocouples were designed and constructed in order to monitor transient surface temperatures. Heat transfer rates were then calculated with the aid of Fourier analysis. Dynamic stresses were monitored by strain-gauges applied to the engine. A special high speed data acquisition system was developed. An existing heat release model was modified and used to calculate combustion rates. A comprehensive finite element model was developed to calculate piston temperatures and stresses. The role of each combustion variable in stress and durability was investigated by statistical analysis. The results successfully identified the causes of combustion related engine failures. The primary cause of engine failure was found to be thermal loading. The principal cause of any variation in thermal loading and thus engine durability was maximum cylinder pressure. The life of the engine was proved to be determined almost entirely by peak cylinder pressure. The role of the rate of pressure rise was proved to be insignificant. All the implications of variations in the nature of combustion can now be determined accurately. It will thus be possible to optimise engine modifications and fuel properties before validation by durability testing.
A diagnostic quasi-dimensional model of heat transfer and combustion in compression-ignition engines.
(1989) Hansen, Alan Christopher.; Meiring, Pierre Andre.
Investigations into the combustion of alternative fuels in compression-ignition engines in South Africa have underlined the inadequacies of existing zero-dimensional combustion models. The major aspect of concern in these models was the computation of heat transfer which had been singled out by a number of researchers as the leading cause of inaccuracies in heat release computations. The main objective of this research was to develop a combustion model that was less empirically based than the existing zerodimensional models for use in evaluating the combustion and resulting thermal stresses generated by alternative fuels. in diesel engines. Particular attention was paid to the development of a spatial and temporal model of convective heat transfer that was based on gas flow characteristics and to the introduction of a radiation heat transfer model that made use of fuel properties and fuel-air ratio. The combustion process was divided into two zones representing burnt and unburnt constituents and the resulting temperatures in each zone were used in the calculations of convective and radiative heat transfer. The complete model was formulated in such a way that it could be applied with the aid of a micro-computer. Calibration and verification of the gas flow sub-models which involved the squish, swirl and turbulence components necessitated the use of published data. Good agreement for the squish and swirl components was obtained between the present model and the experimental data from three engines, two with a bowl-in-piston and the other with a flat piston. These gas flow components dominated the gas velocities in the combustion chamber and provided a reliable foundation for the calculation of convective heat transfer. In spite of the well documented difficulties of characterising turbulence, after calibration the model generated turbulence levels with acceptable trends and magnitudes. Tests were carried out on a naturally aspirated ADE 236 engine involving the measurement of cylinder pressure and heat flux at a single point. Motored engine data were used to verify the convective heat transfer rates and to ascertain the effects of soot deposition on the heat flux probe. Close correlation between predicted and measured heat flux was achieved after accounting for the effects of chamber geometry at the probe site. Soot deposition on the probe caused a significant attenuation of the heat flux within a short period of the engine running under fired conditions. The results from fired engine tests showed that the two zone combustion model was providing plausible trends in the burnt and unburnt zone temperatures and that the model generated combined heat transfer rates which were credible not only on a global basis but also in terms of point predictions in the combustion chamber. The results also highlighted the considerable variation in heat transfer that could occur from one point in the chamber to another. Such variations added considerable weight to the objective of moving away from a zero-dimensional model to a quasi-dimensional type where predictions could be made on a more localised rather than global basis. It was concluded that the model was a definite improvement over zero-dimensional models and competed favourably with existing quasi-dimensional models with advantages in both simplicity and accuracy.
Crop water requirements for irrigation planning in South Africa.
(1988) Dent, Mark Clifford.; Schulze, Roland Edgar.
Irrigation in 1980 accounted for approximately 52 per cent of the water consumed in Southern Africa. The need for planning water resources in the agricultural sector is therefore apparent. Much of Southern Africa's arable farming is carried out on land which, in terms of soil moisture availability to crops, can be described as marginal. Information on soil moisture is therefore valuable to the agriculturalist for planning irrigation schemes and for dryland farming. The objectives of this study were to provide the information mentioned above. This was achieved by producing a detailed delimitation of 712 zones throughout Southern Africa, of more or less homogeneous climate and by providing estimates of crop water requirements under dryland and irrigated conditions in each zone. At the same time the bulk of information which is normally forthcoming from such an analysis involving a large number of combinations of possible input, i.e. crops, soils and planting dates, was reduced, whilst the essential information content was retained. The study provided inter alia an estimate of the frequency of non-exceedance of certain levels of irrigation requirement, based on analyses of soil moisture budgets using long daily rainfall records. The soil moisture budgeting models which were used to estimate the above information were verified inter alia using field measurements of soil moisture. The irrigation analysis was designed such that the results should not became redundant when the inevitable improvement occurs in the estimation of crop factors or soil moisture variables nor if the farming practices change with respect to planting dates. A dryland soil moisture budget analysis for a range of crops and soils was performed in addition to the abovementioned irrigation analysis. The need for this latter study stemmed from the belief that irrigation should not be considered in isolation but rather as one of a range of options, many of them involving dryland farming, facing the agriculturalist. In addition to the dissertation, this study produced a map of Southern Africa on which the 712 homogeneous climate zones are depicted. For each of these zones four pages of computer printout were produced. These pages contain the results of the crop water requirements study for irrigated conditions and the crop water requirement deficit, runoff and an index of stress days for a range of crops, soils and planting dates, under dryland conditions.
The preparation and novel application of diphosphorus xanthene family ligands in homogeneous catalysis.
(2011) Marimuthu, Thashree.; Friedrich, Holger Bernhard.
Abstract available in print version.
The development and evaluation of a performance-based standards approach for regulating the use of heavy vehicles in South Africa.
(2013) Nordengen, Paul Anthony.; Lyne, Peter William Liversedge.; Bezuidenhout, Carel Nicolaas.
The regulation of the use of vehicles on the road network is aimed at ensuring acceptable safety and recovery of road maintenance costs, as well as minimising congestion, road wear, excessive noise and air pollution. The traditional approach of regulating heavy vehicles is prescriptive, i.e. enforcing regulations that primarily limit the mass and dimensions of these vehicles. This approach is generally favoured because such regulations are easy to understand and enforce. However, an underlying disadvantage is that the prescriptive approach does not always adequately safeguard the dynamic performance of heavy vehicles while travelling on the road. Principle-based and performance-based standards are primarily aimed at specifying desired outcomes, rather than how these outcomes should be achieved. Under a performance-based standards (PBS) approach, performance measures (such as low-speed swept path, rearward amplification, load transfer ratio and high-speed offtracking) are utilised to specify the performance required from vehicles. Although more complex to regulate, a PBS approach has a number of potential benefits such as: (a) improved vehicle safety, (b) improved productivity, (c) reduced infrastructure wear and emissions, (d) a more optimal use of the existing road network, and (e) the encouragement of innovation in vehicle design. The aim of this research was to apply, refine and demonstrate an alternative approach to the design and operation of heavy vehicles in South Africa with improved outcomes in terms of road transport productivity, vehicle safety performance, emissions, congestion and preservation of road infrastructure. The research included the development and implementation of a PBS demonstration project in South Africa and the monitoring and evaluation of PBS demonstration vehicles operating in the forestry industry in the provinces of KwaZulu-Natal and Mpumalanga. Evaluation focused on improvements in productivity (fuel efficiency and trip reduction) and load control with reference to initial results regarding road wear and safety performance. Results show a significant improvement in payload control and fuel efficiency of the PBS vehicles compared with the baseline vehicles. This also resulted in a reduction in CO2 emissions per ton.km. Road wear assessments of PBS and baseline vehicles showed that in some cases a reduction in road wear of up to 200% per ton of payload can be achieved through the use of PBS vehicles. Safety assessment results of four PBS vehicle designs showed various shortcomings of prescriptive baseline vehicles in terms of the performance standards.
A comprehensive qualitative and quantitative assessment of harvesting and other sugarcane supply chain disruptions within the Eston Mill supply area.
(2014) Kadwa, Muhammad.; Bezuidenhout, Carel Nicolaas.; Ortmann, Gerald Friedel.
The Eston Mill, which was established in 1994, is the newest in the KwaZulu-Natal sugar belt. Like for most other mills, it can be argued that there are inefficiencies in the supply chain due to systemic issues, which reduce optimum performance. The literature study involved a review of the factors which cause inconsistencies in sugarcane supply chains and the strategies implemented for improvement. This research study involved five main aims. First, a novice qualitative diagnostic analysis of the Eston sugarcane system, to identify a range of systemic issues and one pertinent problem, involving pay-weekends and subsequent labour absenteeism, was isolated for further investigation. This was conducted through explorative interviews and network analysis approaches. Secondly, based on the information from the diagnostic analysis, a model that predicts and quantifies the factors which influence daily crush rate disruptions at Eston, was developed, validated and verified. Thirdly, the extent of the pay-weekend problem area was systematically estimated in terms of frequency, variability and predictability. Fourthly, the cost of cutter absenteeism was conservatively quantified, based on two factors, namely, sugar recovery and mill operational costs. Lastly, a case study was carried out, which involved the feasibility of a mechanical harvesting system, to mitigate the impacts of labour absenteeism. The model involved the calibration of parameters for mill maintenance and operational stops, rainfall events and days in the week when slow crush rates occurred. The model captures approximately 64% of the variation observed in daily crush rates. Subsequent to the development of the model, additional cane supply disruptions, caused by cutter absenteeism, were also investigated. It was statistically verified that a significantly detectable degree of labour absenteeism occurs immediately after pay-weekends. There has been a general increased trend in cutter absenteeism from about 2007 until 2010. An economic analysis estimated the costs associated with cutter absenteeism to be approximately R1.3 million per season, for the Eston region. The alternative harvesting system case-study solution, was found to be risky. However, acquiring second-hand equipment, which was available on the market, is estimated to make the solution more feasible. Based on a literature search, this research is considered to be the most comprehensive analyses of sugarcane supply consistency at mill-scale worldwide. The model developed can be utilized to critically evaluate different sugarcane milling areas and could potentially make significant contributions to commercial sugarcane operations. The effectiveness of the model is dependent on usage in other milling areas, as well as other industries. In addition, the specific labour absenteeism coefficients for each season can possibly be investigated using other industries as well.
An assessment of the feasibility of quality indicators for the postharvest deterioration of sugarcane (Saccharum officinarum L.)
(2014) Sibomana, Milindi Sylver.; Bezuidenhout, Carel Nicolaas.; Workneh, Tilahun Seyoum.; Sobratee, Nafisa.; Rutherford, Richard Stuart.
Sugarcane deterioration remains one of the most important supply chain efficiency leverage points in the South African sugar industry. Cane quality has been identified as an issue that has the potential to improve the overall efficiency of the sugarcane supply chain. A review comparing the postharvest quality management systems and measurements in the South African sugar and fresh produce industries was conducted. The difference in postharvest handling between the two industries was found to be an important factor dictating quality management. Advances in non-destructive quality measurement techniques and sanitation strategies were found in the fresh produce industries, which could be adopted by the South African sugar industry. An empirical study of standard sugar industry cane quality parameters was also performed. Sugarcane quality parameters measured at the Felixton mill were analysed, per ward, using quality control charts and non-parametric statistical approaches. A daily analysis of these parameters, as well as the Pol % Fibre ratio, using Shewhart quality control ( x ) charts revealed that, overall, Monday deliveries were of significantly lower quality (P<0.01). This is a quantitative indicator of logistics (or management) inefficiency over the weekend. Using the Mann-Whitney test, Pol % Fibre was used to generate a grower performance index, based on high levels of statistical significance (P<0.05), which may allow stakeholders to improve operations, through identifying the levels at which individual growers deliver significantly (P≤0.05) lower quality cane in the early part of the week. This study uncovered new and significant statistical trends within the sugar industry's quality database and demonstrates the potential of Pol % Fibre as an indicator of quality inferiority in the cane supply chain. To further investigate cane deterioration in this context, two burn/harvest-to-crush delay trials involving two sugarcane varieties (N12 and N31), which were exposed to ambient environmental conditions for a period of nine days after harvest were performed. On sampling dates, each variety was tested for quality parameters such as total bacterial counts, D-lactate production, and respiration. Standard sugar industry quality parameters and Pol % Fibre were also monitored. Parameters were measured in bottom, middle and top portions of the stalks to evaluate the effect of section on the parameter changes. Trial 1 was conducted on unburnt cane in October 2012 and Trial 2 on burnt cane, April-May 2013. Stalk portion significantly (P<0.001) affected the parameters, with the top and bottom portions showing higher bacterial proliferation, respiration rates and D-lactate production compared to the middle portion in Trial 1. Trial 2 showed no significant variability in stalk portion. In Trial 1, a significant (P<0.05) declining trend was noted for Brix % DM and Pol % Fibre in the top portion. The effect of higher respiration in the cut-ends in Trial 1 was noted in significantly reduced Pol % Fibre in these cut-ends. Environmental conditions were found to be the major factor influencing quality during the cane storage period. The study concludes, from both analysis of CTS data and the results of the BHTCD trials, that Pol % Fibre can be monitored at sugar mills as an additional parameter for signalling inferior quality and deterioration of cane consignments.
Non-point source pollution processes and connectivity modelling in the Mkabela Catchment, South Africa.
(2015) Kollongei, Kipkemboi Julius.; Lorentz, Simon Antony.; Chaplot, Vincent A. M.
In South Africa water resources and water quality issues are becoming increasingly important as the country manages its scarce water resources. The National Water Act of South Africa Act 36 (1998) stipulates that water resources must be shared in a sustainable fashion among humans, environment and economic land uses. Deterioration of water qualities in rivers are not only unique problems to South Africa. Indeed the degradation of water quality by nutrients originating from agriculture through excessive use of fertilizers (NO₃ and P) and erosion (sediments) is an international environmental concern. Rivers passing through agricultural areas experience high pollution levels from non-point sources resulting from these agricultural activities. Dealing with this issue is not straight forward because the agricultural contribution to diffuse pollution varies widely as a complex function of soil type, climate, topography, hydrological connectivity, land use and management. This creates widespread, intermittent, and poorly defined contaminant sources that degrade water quality in a way that makes their control difficult. In recognition of the accelerated degradation of water bodies from agricultural Non-Point Source (NPS) pollutants, watershed models have evolved from traditional hydrology models to more comprehensive water quality models. Diminished use or even loss of the water resource for other beneficial uses has resulted from over burdening of the receiving waters with waste fertilizers from agriculture. For example, many surface and groundwater bodies used as a water supply have lost their utility due to agricultural pollution. Upstream users of land do not feel the economic impact of their action on the downstream users who must use water from other sources because the water quality of their source was rendered unusable. Farmers respond to their economic realities, i.e. they want to make at least some profit or at least survive during harsh economic situations, both of which can be accomplished by increased crop yields. Without some intervention in the farmers’ economic reasoning, the potential water quality problems far downstream is not a part of the farmers’ decision making process with regards to how much fertilizers they will use on their land or how to dispose of their animal waste. The new ACRU-NPS (Agricultural Catchment Research Unit- Nitrogen, Phosphorous and Sediments) model was developed to try to address these challenges. The model was configured using a nested approach, which requires an effective description of all relevant components of the system and an understanding of the processes and feedbacks taking place within and between different scales and hydrological processes response zones. The concept of connectivity in the model was introduced to improve simulations. Connectivity defines the physical coupling of landforms (e.g. hillslope to channel) within a catchment where the passage of water from one part of the landscape to another is expected to generate a catchment runoff response that may carry along with it dissolved pollutants, sediments and any contaminants that they may carry through the drainage basin. The connectivity of the river (drainage) network in the Mkabela Catchment (near Wartburg, KwaZulu-Natal) was assessed on a sub-catchment basis and was linked to in-stream controls that included farm dams, wetlands and buffer zones where the fate and transport of dissolved N and P, sediment and associated adsorbed P were studied. A new method of calculating crop yield, different from that used in the SWAT (Soil and Water Assessment Tool) model, was developed and incorporated in the ACRU-NPS model. In the new method water and nitrogen stresses were used to limit crop growth on a daily time step. This enabled consequences of subsequent nutrient and sediment loads in streams to be studied. The major limitation to long-term use of SWAT in South Africa is the lack of long-term nutrient and suspended solids data for calibration and validation. This study utilized the new ACRU-NPS modelling approach to study pollutants emanating from the Mkabela Catchment in South Africa. The developed ACRU-NPS model included sufficient process details to allow for the implementation of controls such as wetlands, dams and buffer strips. Successful simulation of crop yields, nutrient and sediment production, together with the fate of NPS pollutants, for various land uses was thus achieved. The major contribution of this study however was to link hydrology and NPS pollution processes by describing and defining pathways through which pollutants moved in the catchment. This was achieved through studying the dynamics and connectivity of water, sediments and nutrient fluxes by combining hydrometric, hydropedological, geophysics and stable water isotope techniques to interpret the field and laboratory data. Suggestions for future improvements on the ACRU-NPS model were given based on the understandings gained from the different observations and sampling done in the Mkabela Catchment.
Using system dynamics to explore the poor uptake of irrigation scheduling technologies in a commercial sugarcane community in South Africa.
(2016) Jumman, Ashiel.; Bezuidenhout, Carel Nicolaas.
Abstract available in PFD file.
Development and application of decision support systems for improved planning and operation of large dams along the White Nile.
(2015) Zaake, Benon Tamukedde.; Smithers, Jeffrey Colin.
In this study the regulation of Lakes Victoria, Kyoga and Albert in East Africa are investigated with the objective of maximising hydropower production subject to system constraints for existing and future planned dams along the Upper White Nile in Uganda. A Decision Support System (DSS) has been assembled and applied to search for efficient lake-reservoir operating rules for this basin. Elements of the DSS include power plant functions, a simulation model of the Upper Nile Equatorial Lake Basin, the Stochastic Analysis Modelling and Simulation (SAMS) computer software package for analysing hydrologic time series and the Colorado State University Dynamic Programming (CSUDP) model for solution of the optimisation problem. A concurrent record of observed lake levels and outflows for the three lakes during the reference period 1899 – 2008 has been constructed from various long term monitoring stations and utilised to derive net basin supply or net inflow time series at a monthly and annual time scale. Statistical tests confirmed the non-stationarity of the annual lake net basin supply time series. A justification to model the stochastic process of the monthly inflows as a Markov process was also reached. A Univariate Shifting Mean model was fitted to the annual historical data in tandem with a model for temporal disaggregation of annual to monthly net basin supplies for the purposes of generating synthetic flow series. The model performed well in terms of preserving the statistical characteristics of the historical reference set for each lake. The synthetic time series are considered to be a useful reference data set for future research in generating reservoir operating rules. Two Dynamic Programming (DP) models that may be used to generate reservoir operating rules were investigated. The desired scope of optimization was however curtailed by the well-known dimensionality problem of DP. Application of the deterministic method of Incremental Dynamic Programming (IDP) to the optimisation problem could only be carried out on a monthly time step and for single years separately. Annual time step optimization could only be carried out for the historic net inflows. The 1000 stochastically generated time series of net basin supplies could not be utilized within the implicit framework of deriving operating rules due to impractical computational requirements. The IDP however, yielded a realistic set of optimal operating policies at an annual time scale for the historical reference period (1898 – 2008). The beginning of year lake levels and annual release magnitudes obtained were compared against similar data for natural unregulated lake conditions. It is concluded that, in general, lake regulation would yield desirable benefits in terms of hydropower generation but would lead to marked deviation from natural lake levels and more variable outflows. The Stochastic Dynamic Programing (SDP) model was only applied to Lake Victoria in single reservoir optimization scheme due to limitations imposed by the large dimensionality of the problem and difficulty of simultaneously incorporating multiple lake reservoir transition probability matrices in the model. Application of the model for Lake Victoria showed that, it was feasible to define final storage levels for discretized initial storage and previous period inflow class combinations. The results from the study indicate that realistic heuristic operation rules can be inferred from the results of applying the IDP models and SDP algorithm.
Estimating traffic induced sugarcane losses for various harvesting, loading and infield transport operations in South Africa.
(2016) Tweddle, Peter Brian.; Lyne, Peter William Liversedge.; Lagerwall, Gareth.
Infield traffic has been understood to cause adverse field conditions for crop growth. Literature containing traffic induced yield responses for sugarcane was reviewed and synthesised to better estimate the impact of infield traffic on sugarcane yields. Approximately 128 sugarcane yield responses to infield traffic treatments from local and international trials were collated and analysed. The impact of soil compaction effects on soil properties were not considered as there is a substantial body of knowledge on this topic. The results confirm that traffic on a sugarcane row is more detrimental than inter-row traffic. Soil water content at the time of infield traffic and infield traffic load intensity are further critical factors affecting soil compaction and sugarcane yield. Further aggregation of the data by soil textural groups was found to establish yield response trends useful for modelling of infield traffic scenarios, but were not statistically significant. Infield traffic paths of equipment movements were surveyed and mapped for a range of typical harvesting systems found commercially in the South African sugarcane industry. The maps were analysed to proportion the field area by row traffic, inter-row traffic and remaining non traffic areas for each machine component used infield. Yield losses based on vehicle traffic impacts were assigned to each corresponding component as determined from the results of the literature synthesis. The traffic induced yield loss was apportioned to the areas trafficked to determine a field based yield loss estimate for each of the harvesting and extraction systems and a corresponding economic impact reported. The ranking of system costs, reported off a mechanisation costing base, altered when the additional field traffic induced yield loss components were added, particularly when yield losses were compounded across multiple ratoons within a cropping cycle. Systems operating with low impact vehicles, of low traffic extent combined with controlled traffic practices resulted in the lowest yield losses on a field basis and also resulted in the lowest overall cost. Controlled traffic practices reduce the impact of heavy infield equipment on yields. The significance of this work is that the yield losses due to infield traffic can now be attributed to systems to allow for improved costing analyses and system comparisons to be conducted. It is proposed that this new contribution be incorporated into standard mechanisation costing methodologies to allow for such crop yield losses to be accounted for.
Technological viability of coffee husk ash, soil rich in koalinite-ferrinatrite and koalinite-geothite for the adsorptive removal of chromium (VI) from industrial wastewater = Ukusebenziseka kobuchwepheshe bomlotha wekhofi i-husk, inhlabathi enothile ngeKaolinite-Firrinatrite kanye neKaolinite-Geothite ekukhucululeni okusansimbi okuphuma emanzinimfucuza yasezimbonini.
(2017) Samuel, Zerihun Asmelash.; Workneh, Tilahun Seyoum.; Trois, Cristina.; Feyessa, Fekadu Fufa.
ABSTRACT: Most industries in developing countries discharge a high amount of untreated wastewater, containing toxic chemicals, into nearby water bodies. Heavy metals and chemicals above permissible levels can be emitted to the environment as wastewater effluents from industries such as leather, electroplating, tanning, metal, fertilizer, and other industries. When these are discharged into the environment, they significantly pollute the quality of the water bodies and the environment, thereby substantially affecting river and human health. The safe and effective purification of polluted water containing heavy metals is always a challenge in many parts of the world, because cost-effective treatments are not readily available. Various methods are used for removing heavy metals, such as irradiation, chemical precipitation, ion exchange, adsorption, biological and chemical treatment. However, the adsorption technique is the best option due to easy to operate, simple, cheap, efficient, and suitable for the environment. The adsorption method is a suitable technique for developing countries like Ethiopia, where the advanced wastewater treatment technologies for high amount of toxic industrial wastewater are unaffordable. Locally-available adsorbent materials reasonably meet the criteria that have been established for the wastewater treatment process, due to their natural availability as adsorbents, their high natural porosity, their very low price, easy design, operation and maintenance, as well as their suitability for pollutant adsorption. The applicability of low-cost, locally-available adsorbent materials for the adsorptive removal of heavy metals from industrial wastewater is important. This study investigated the technological viability of low-cost materials, such as coffee husk ash, soil that is rich in kaolinite (40.4%) and ferrinatrite (59.6%), and soil that is rich in kaolinite (29.4%) and goethite (70.6%), for the adsorptive removal of chromium from industrial wastewater. The physical properties and elemental composition of the three adsorbents (soil rich in kaolinite-ferrinatrite, coffee husk ash and kaolinite-geothite) were characterized. The experiments were conducted under batch adsorption set-ups to assess the effect of different parameters and their optimum removal efficiency. The optimum adsorption of Cr(VI) on the three adsorbents used were observed at 40 minutes and two pH values and their doses of adsorbent, shaker speed, and initial Cr (VI) ion concentration were different in the batch adsorption experiments. The adsorption of Cr(VI) followed pseudo second-order kinetics, with a coefficient of determination r2 > 0.99 for the three-adsorbent media. Results of the adsorption isotherm show that Freundlich adsorption isotherm model better described Cr(VI) adsorption into soil rich in kaolinite-ferrinatrite (SRKF), soil rich in kaolinite-geothite (SRKG) and coffee husk ash (CHA) with coefficients of determination; r2 > 0.93. The adsorption capacity of the adsorbent followed the decreasing order CHA >SRKF > SRKG. The findings on the adsorption characteristics of batch system from this work suggests that soil rich in kaolinite-ferrinatrite, coffee husk ash and soil rich in kaolinite-goethite could represent an interesting low-cost naturally available adsorbent material that could be used for the chromium (VI) removal from wastewater. The empirical data and models developed in the study were used to establish theoretical design analysis of adsorptive treatment plant for industry emits such wastewater. However, further investigations will be required for the practical application of these locally-available adsorbent materials for the removal of chromium from wastewater. IQOQA LOCWANINGO:Izimboni eziningi emazweni asathuthuka zikhipha amanzimfucuza amaningi achithwa engahlanzwanga, anamakhemikhali nobuthi, ezindaweni zokuchitha amanzi. Imfucuzamanzi yesikhumba, i-electroplating, i-tanning, okusansimbi, isivundisi, nobunye ubuxhamaxhama, bunamakhemikhali kanye nokusansimbi okunobungozi obungaphezu kwezinga elivunyelwe. Uma konke lokhu sekuchithwe emphakathini, kungcolisa kakhulu izindawo zokuchitha amanzi kanye nendawo, ngaleyo ndlela kuphazamisa impilo yamanzi kanye nempilo yabantu. Indlela ephephile nesebenzayo yokuhlanza amanzi angcolile anokusansimbi okusindayo kuhlale kunezinqinamba ezindaweni eziningi emhlabeni, ukuhlanzwa okungabizi kakhulu akutholakali kalula. Izindlela ezahlukahlukene zisetshenzisiwe ukukhipha okusansimbi okusindayo, njenge- irradiation, ukusefa amakhemikhali, ukushintsha inhlasigesi, i-adsorption, ukuhlanzwa kwamakhemikhali nokuphilayo. Kodwa-ke isu le-adsorption yilona elidla ubhedu ngenxa yokuthi lenzeka kalula, lisobala, alibizi, lisebenza kahle, futhi liyifanele indawo. Uma sibheka uhlaziyo olungenhla, indlela ye-adsorption yilona lisu elifanele lamazwe asathuthuka afana ne-Ethiopia, lapho ubuchwepheshe obusezingeni eliphezulu bokuhlanza amanzi ebuthini obuningi obusuka emfucuzeni yamanzi asezimbonini lungakwazi ukuthi lwenzeke. Amathuluzi okusebenza ekhaya akhona e-adsorbent ahambisana kahle nezimo zokwenza ezakhiwe uhlelo lokwelapha amanzimfucuza ngenxa yokubakhona kwama-adsorbents ngokwemvelo, ukuba khona kwezimbotshana kwalo ngokwemvelo, amanani aphansi, umumo olula, ukusebenziseka kanye nokugcineka kwalo, nokulungela kwalo i-adsorption engcolisekile. Ukuba khona kwamanani aphansi, amathuluzi akhona e-adsorbent ekhaya okususa okusansimbi okusindayo kwe-adsorptive kumfucuzamanzi yasezimbonini kubalulekile. Lolu cwaningo luhlole ukuthi amathuluzi enani eliphansi obuchwepheshe angasebenza yini, njengomlotha wekhofi i-husk, inhlabathi enothile ku-kaolinite (ama-40.4%) ne-ferrinatrite (ama-59.6%), kanjalo nenhlabathi enothile ku-kaolinite (ama-29.4%) ne-goethite (70.6%), yokususa i-adsorptive ye-chromium kumfucuzamanzi yasezimbonini. Amalinge enziwa ngaphansi kwe-batch ye-adsorption eyenzelwe ukuhlola umthelela wamapharamitha ahlukahlukene kanye nokusuka kwawo ngokuphelele. I-adsorption ephelele yenhlabathi enothe nge-kaolinite-ferrinatrite, umlotha wekhofi i-husk kanye ne- kaolinite-goethite yabonwa ngokujwayelekile emizuzwini engama-40 kanye namaveluzi amabili e-pH kanye namadosi e-adsorbent, ijubane le-shaker, kubandakanya i-Cr yokuqala (VI) ubukhona be-ion babuhlukile kuma-batch amalinge e-adsorption . I-adsorption Cr(VI) ilandele i-pseudo second-order kinetics, inokudlelana ne-coefficient engama-R2 > 0.99 ngama-adsorbent amathathu ezokukhangisa. Imiphumela ye-adsorption isotherm ikhombisa ukuthi imodeli ye-Langmuir adsorption isotherm echazwa kahle njenge-Cr (VI) adsorption enhlabathini enothe nge-kaolinite–ferrinatrite (i-SRKF), inhlabathi enone nge-kaolinite–geothite (SRKG) kanye nomlotha wekhofi i-husk (i-CHA) nobudlelwano obuyi-coefficient; ama-R2 > 0.93. Umthamo we-adsorption ye-adsorbent kungahlelwa ngendlela eyehlayo i-CHA >SRKF > SRKG. Okutholakele emisebenzini ye-adsorption yezinhlelo zama-batch kulo msebenzi kuphakamisa ukuthi inhlabathi enothile ku-kaolinite-ferrinatrite, umlotha wekhofi i-husk kanye nenhlabathi enothe ku-kaolinite-goethite ingamelela izinto ezitholakala ngenani eliphansi ngokwemvelo ze- adsorbent ezingasetshenziselwa i-chromium (VI) ukususwa kumanzimfucuza. Ulwazi oluhloliwe locwaningo kanye namamodeli akhiwe ocwaningweni asetshenziswe ukwakha umumo wokuhlaziya wenjulalwazi yomshini wokwelapha i-adsorptive embonini eqokiwe. Yize kunjalo, kusadingeka ukuthi kwenziwe ucwaningo oluzoveza ukusebenza-ke manje kwale-adsorbent etholakala ekhaya esusa i-chromium kumanzimfucuza.
Effect of maturity and postharvest handling of prunus persica ‘landrace’ produced in KwaZulu-Natal: case study of physicochemical properties, tunnel solar drying and quality of processed products.
(2017) Mkhathini, Khangelani Maxwell.; Workneh, Tilahun Seyoum.; Mwithiga, Gikuru.; Magwaza, Lembe Samukelo.
Farmers in KwaZulu-Natal produce peach fruit. However, they are faced with overwhelming losses of the fruit due to lack of proper handling techniques, skills and facility during postharvest. In addition, these farmers have limited formal markets where they could sell fresh fruit immediately after harvesting. Thus, they are forced to consume the least they can and leave the rest of the fruit hanging on the tree. As a result, they lose close to 45% of their fruit. The literature review congruently pointed out such challenges of food losses in less developed countries and South Africa is not an exception. With a limited understanding of peach properties, it becomes increasingly difficult for farmers to handle the fruit. The cost of storage and processing facilities (such as sophisticated refrigeration) is very high and a decision table was used to determine which affordable method can be employed to process the peach fruit. The study is significantly important for the reduction of massive losses of fresh produce in the small-scale household farming sector as whole in South Africa. This study had three main aims to address. Firstly, it aimed to understand the physiological maturity and ripening of the peach fruit by determining physicochemical properties such as days to maturity, mass, volume, shape, moisture, pH, total soluble solids, colour (CIELab) and firmness. Secondly, the study aimed to install and test a tunnel solar dryer according to a decision table criteria that used to decide on a fruit processing method. Thirdly, the study aimed to process the fruit into dried peach slice with pre-treatments of lemon juice (LJ), ascorbic acid (AA) and a control, using a tunnel solar dryer. In addition, the study also aimed to process the peach into dried peach leather also using a tunnel solar dryer. This study included both objective and subjective methods to test the quality of the peach slice and leather products processed. Fruits reached maturity 129 days after full bloom (DAFB) and this coincided with fruit mass, volume and moisture content at respective averages of 80.00 g, 66.10 cm3, and 83%. Fruit firmness decreased significantly from 79.00 N to 24.70 N with increasing ripeness. Total soluble solids increased significantly from 13.50 to 19.00 °Brix during ripening. The pH value significantly increased from 3.40 to 4.00 indicating that acidity decreased with ripening. The TSS: TA ratio increased from 21.11 to 35.84. Moreover, it has been statistically verified that due the colour, yellow peach fruit produced the best products (as seen by the receipt of the highest sensory evaluation overall acceptability scores and based on the texture profile analysis results provided by Texture Analyser instrument). The utilisation of treatment such as AA or LJ did not have a significant effect in the overall drying between the yellow and white landraces. Ascorbic acid had a tendency to perform better than LJ which was also better than the untreated slices (control) in terms of the taste and overall acceptabilty. The experiment revealed that white leather moisture was approximately 7% and received the lowest overall acceptability scores from panellists. Less quality results were also received according to the texture profile analysis, in contrast to the yellow peach leather, which had 13% of moisture content. Yellow leather received the highest overall acceptability scores by both texture profile analysis and sensory evaluation tests. Thus, this study suggests that drying is possible in the KwaZulu-Natal Midlands. Overall, the results developed from the current study demonstrate that the fruit produced in small-scale farming sector is of good quality regardless of low yields because fertilizers and pesticides are not used. More importantly, this study reveals the significant potential of solar drying to be used by small-scale farmers to develop on-farm interventions aiming to add value to their produce and thus be able to preserve, use and sell later. It was concluded that DAFB, firmness, mass, TSS, volume, TTS: TA ratio are potential parameters to be used for maturity indexing of white peach ‘landrace’. Regardless of the misty conditions that prevail during the period of harvesting fruits, it was concluded by a statistical significant difference that the tunnel solar drying is a possibility in the KwaZulu-Natal Midlands. Days after full bloom, firmness, TSS, pH and mass have a critical role to play since they significantly differ between different ripeness degrees. These can be used to monitor peach growth stages and estimate yield for the small-scale peach grower in the area. The DAFB are a good tool that farmers can stick to without the use of advance technologies other than monitoring the number of days. Firmness is also a very important parameter for farmers in the area as the fruit hardly changes colour but can be soft showing signs of ripeness. The study has also devised a step-by-step process, which can be followed by small-scale processors in order to reduce losses using solar dryer to process fruit into leather and slice.
Development and optimization of an integrated post-harvest management system for the handling and storage of fresh tomatoes in South African supply chains.
(2017) Cherono, Kipchumba.; Workneh, Tilahun Seyoum.
Abstract available in PDF file.
Soil water dynamics and response of cowpea to water availability under moisture irrigation.
(2019) Kanda, Edwin Kimutai.; Senzanje, Aidan.; Mabhaudhi, Tafadzwanashe.
Increasing population, urbanization and industrialization has put pressure on the irrigation sub-sector to produce more yield using less water i.e. improving crop water productivity (WP). This can be achieved through the adoption of efficient irrigation systems such as micro-irrigation. Moistube irrigation (MTI) is a relatively new technology like subsurface drip irrigation (SDI) but with a semi-permeable membrane whose nanopores emit water in response to applied pressure and soil water potential. Being a new technology, there is little information regarding its hydraulic characteristics and soil water distribution which are necessary for its design, operation and management. Furthermore, the response of crops under a variety of soils and environmental conditions under MTI has not been covered extensively. Therefore, this study aimed at determining the hydraulic and clogging characteristics of MTI. The effect of soil texture on the soil water dynamics of MTI was also determined. Finally, the response of cowpea, an important but neglected African indigenous legume, to varying water regimes under MTI was also determined. This study was based on the hypothesis that cowpea responds favourably to water regimes under MTI. The study was accomplished through laboratory, field experiments and agro-hydrological models. AquaCrop and HYDRUS 2D/3D were chosen for this study due to their reliability in predicting crop yield responses to water availability and soil water dynamics respectively. The laboratory experiments were conducted in soil bins to determine the soil water dynamics of MTI under sandy clay and loamy sand soils which were used to calibrate the HYDRUS 2D/3D model. The hydraulic characteristics were determined at a pressure of between 10 kPa and 100 kPa while the effect of suspended and dissolved solids was determined under a pressure of 20 kPa and 30 kPa. The field experiments consisted of glasshouse and tunnels to examine the response of cowpea to full and deficit irrigation of MTI with SDI as the control. The results were used to parameterise and validate the AquaCrop model. Finally, HYDRUS 2D/3D and AquaCrop were coupled to draw into the strengths of the individual models and used to simulate the water use of cowpea under MTI in two agro-ecological zones in South Africa. The results showed that the discharge – pressure relationship of Moistube followed linear and power functions. It was also established that suspended solids had severe clogging effect than dissolved solids. In the soil bin experiment, simulated water contents closely matched (R2 ≥ 0.70 and RMSE ≤ 0.045 cm3 cm-3) the observed values in all the points considered for the two soil textures. The model slightly under-estimated or over-estimated the soil water content with percent bias less than 15.6%. There was no significant difference (p > 0.05) between the soil water distribution in lateral and downward direction for both sandy clay loam soil and loamy sand. However, the soil water content upward of the Moistube placement depth was significantly lower (p < 0.05) than both the lateral and downward soil water contents in loamy sand. The soil water dynamics under MTI while incorporating the root water uptake indicated that there was no significant difference between the root water uptake in SDI and MTI (p > 0.05). Water loss through drainage was significantly higher (p < 0.05) under SDI than MTI in loam while it was negligible in clay for both irrigation types. Drainage increased with increased Moistube placement depth. The interaction between the distribution of root water uptake and the soil water distribution indicated that a suitable placement depth for cowpea under MTI was 15 cm in loam and 20 cm in clay. There were no significant differences (p > 0.05) in the yield response of cowpea between MTI and SDI but the latter performed better under deficit irrigation conditions. AquaCrop model was parameterized and tested successfully under full and deficit irrigation. The results indicated the model simulated the canopy cover (CC) very well with R2 ≥ 0.85, RMSE ≤ 24.5%, EF ≥ 0.45, and d ≥ 0.87. The simulated water content closely matched the observed with R2 ≥ 0.61, RMSE ≤ 11.3 mm, EF ≥ 0.51, and d ≥ 0.86 indicating that the model reasonably captured the soil water dynamics. Generally, yield and biomass were simulated satisfactorily by the model with R2 of 0.84 and 0.88, and RMSE of 282 kg ha -1 and 1307 kg ha -1, respectively, during parameterisation. Similarly, during model testing the model performance was very good with R2 of 0.96 and 0.99, and RMSE of 165 kg ha -1 and 798 kg ha -1 for yield and biomass, respectively. The highest WP was achieved under 70% ETc (crop water requirement) and 40% ETc for yield and biomass, respectively. Having successfully calibrated and tested the HYDRUS 2D/3D and AquaCrop models, the two were used symbiotically to simulate the water use of cowpea in two environments characterized by clay and sandy soils. The crop characteristics were obtained using AquaCrop while HYDRUS 2D/3D was used to generate optimum irrigation schedules and the soil water balance. Thereafter, the water use and yield of cowpea was determined. The average grain yield and biomass were 2600 kg ha-1 and 10000 kg ha-1, respectively, with the difference between the two sites being less than 5% under both SDI and MTI. The water use and WP varied from 315 mm to 360 mm and 0.67 to 1.02 kg m-3, respectively, under the two irrigation types at the two sites considered. The WP was higher under SDI than MTI, but the differences were less than 10%. This showed that cowpea responded similarly under MTI and SDI. Further research is needed on the determination of the clogging characteristics due to fertigation. Finally, more field experiments under other environmental conditions need to be carried out to validate the results of this study.
Investigating the effects of irrigation water management techniques using anaerobic baffled reactor (ABR) effluents for crop production.
(2018) Busari, Isiaka Toyin.; Buckley, Christopher Andrew.; Odindo, Alfred Oduor.; Senzanje, Aidan.
The discharge of treated effluents from anaerobic baffled reactor (ABR) into surface and ground water bodies poses a challenge to the environment and can cause pollution. The need for the optimal use of land without a yield penalty in urban and peri-urban (UP) settlements such as Newlands KwaMashu Experimental site, Durban, South Africa is vital. The volume of ABR effluent generated by a decentralized wastewater treatment systems (DEWATS) in UP settings increased with population, urbanization and improved living conditions. Hence, the need to cultivate effluent irrigated crops is paramount and synonymous to treated wastewater reuse and management. Therefore, the study evaluated the effects of irrigation management techniques and intercropping on the growth and yield of flood irrigated Cocoyam (colocasia esculenta) and rice (oryza sativa l.) using ABR effluents. It was hypothesised that irrigation management techniques and intercropping do have a significant effect on the growth and yield of Cocoyam and rice irrigated with treated domestic wastewater An open field trial using basin (flood) irrigation with ABR effluent and a pot experiment inside a tunnel house, for zero effective rainfall, were conducted concurrently with the same treatments in 2017 and 2018 planting seasons at the Newlands KwaMashu Experimental site, Durban, South Africa. The irrigation water management treatments consisted of alternate wetting and drying (AWD), conventional flood irrigation (CFI) and continuous wetting without flooding (WWF) and the cropping systems were sole Cocoyam, sole rice and intercropped Cocoyam and rice. The treatments with WWF was the control for Cocoyam and CFI was control for rice. Each of the treatments was replicated three times in a randomized complete block design (RCBD) layout. Cocoyam from the open field and pot trials showed that the effects of the treatments were significant (P < 0.05) on the number of irrigation events, amount of irrigated water and daily water balance. The treatments had no effect on the growth parameters (plant height, leaf number and leave area index (LAI) (P > 0.05)). The treatments effects were, however, highly significant (P < 0.001) with respect to yield components (biomass, corm mass, corm number, corm size, harvest index), corm yield and water productivity (WP). The control (WWF) produced the highest yields of 7.52 and 9.84 t/ha for 2017 and 2018 seasons, respectively for field trials. The control (WWF) produced the highest yields of 4.97 and 6.40 t/ha for 2017 and 2018 seasons, respectively for pot trials. The result for field and pot trials for rice revealed that the effects of irrigation management techniques were highly significant (P < 0.001) on number of irrigation events, amount of irrigation and daily water balance. However, there were no significant differences (P > 0.05) between irrigation management techniques with respect to the number of tillers per plant but significant (P < 0.05) on the number of panicles per plant. Similarly, irrigation management treatments did not differ significantly (P > 0.05) with respect to plant height and leaf area index (LAI). Significant differences (P < 0.05) were observed with respect to rice yield, though the treatment was not significant (P>0.05) with respect to rice yield in 2018 season. The effect was also significant (P < 0.05) on water productivity. The treatments AWD produced the highest grain yields of 5.68 in 2017 and 6.38 t/ha in 2018 season for field trials. The AWD treatments had the highest yields of 2.32 and 3.21 t/ha for 2017 and 2018 seasons, respectively for pot trials. The effect of intercropping was significant (P<0.05) with respect to the total number of irrigation and total water use. There was a significant reduction (P<0.05) on the plant heights of both Cocoyam and rice under intercropping. A significant (P<0.05) reduction also occurred on the number of Cocoyam leaves per plant, number of panicles per plant and number of tillers per plant for rice. Intercropping significantly reduced (P<0.05) the Cocoyam corm and rice grain yield over the two seasons as compared to sole cropping. The land equivalent ratio (LER) showed that intercropping Cocoyam with rice was not productive (LER < 1) than sole cropping of Cocoyam. It was established that there was no significant (P>0.05) effects of the treatments with respect to the growth parameters but was significant on the yield of sole Cocoyam and sole rice. The yields of Cocoyam under intercropping were 4.96 and 6.96 t/ha for 2017 and 2018 seasons while grain yields under intercropping were 0.84 and 1.0 t/ha for 2017 and 2018 seasons. This study concluded that both AWD and CFI resulted in yield reduction and WP as compared to WWF, and as such, not recommended for Cocoyam production in order to improve the productivity. AWD irrigation with ABR effluent should be encouraged among rice farmers and therefore, recommended among the rice farmers closer to ABR effluents. It was also concluded that over the two season period, intercropping Cocoyam and rice was not productive under any of the three irrigation management techniques applied. The hypothesis is thus accepted for yield and rejected for the growth parameters.
Developing a diagnostic heuristic for integrated sugarcane supply and processing systems.
(2019) Shongwe, Mduduzi Innocent.; Bezuidenhout, Carel Nicolaas.; Bodhanya, Shamim Ahmed.
Innovation is a valuable asset that gives supply chains a competitive edge. Moreover, the adoption of innovative research recommendations in agricultural value chains and integrated sugarcane supply and processing systems (ISSPS) in particular has been relatively slow when compared with other industries such as electronics and automotive. The slow adoption is attributed to the complex, multidimensional nature of ISSPS and the perceived lack of a holistic approach when dealing with certain issues. Most of the interventions into ISSPS often view the system as characterised by tame problems hence, the widespread application of traditional operations research approaches. Integrated sugarcane supply and processing systems are, nonetheless, also characterised by wicked problems. Interventions into such contexts should therefore, embrace tame and/or wicked issues. Systemic approaches are important and have in the past identified several system-scale opportunities within ISSPS. Such interventions are multidisciplinary and employ a range of methodologies spanning across paradigms. The large number of methodologies available, however, makes choosing the right method or a combination thereof difficult. In this context, a novel overarching diagnostic heuristic for ISSPS was developed in this research. The heuristic will be used todiagnose relatively small, but pertinent ISSPS constraints and opportunities. The heuristic includes a causal model that determines and ranks linkages between the many domains that govern integrated agricultural supply and processing systems (IASPS) viz. biophysical, collaboration, culture, economics, environment, future strategy, information sharing, political forces, and structures. Furthermore, a diagnostic toolkit based on the Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) was developed. The toolkit comprises a diagnostic criteria and a suite of systemic tools. The toolkit, in addition, determines thesuitability of each tool to diagnose any of the IASPS domains. Overall, the diagnostic criteria include accessibility, interactiveness, transparency, iterativeness, feedback, cause-and-effect logic, and time delays. The tools considered for the toolkit were current reality trees, fuzzy cognitive maps (FCMs), network analysis approaches, rich pictures (RP), stock and flow diagrams, cause and effect diagrams (CEDs), and causal loop diagrams (CLDs). Results from the causal model indicate that collaboration, structure and information sharing had a high direct leverage over the other domains as these were associated with a larger number of linkages. Collaboration and structure further provided dynamic leverage as these were also part of feedback loops. Political forces and the culture domain in contrast, provided lowleverage as these domains were only directly linked to collaboration. It was further revealed that each tool provides a different facet to complexity hence, the need for methodological pluralism. All the tools except RP could be applied, to a certain extent, across both appreciation and analysis criteria. Rich pictures do not have causal analysis capabilities viz. cause-and-effect logic, time delays and feedback. Stock and flow diagrams and CLDs conversely, met all criteria. All the diagnostic tools in the toolkit could be used across all the system domains except for FCMs. Fuzzy cognitive maps are explicitly subjective and their contribution lies outside the objective world. Caution should therefore be practiced when FCMs areapplied within the biophysical domain. The heuristic is only an aid to decision making. The decision to select a tool or a combination thereof remains with the user(s). Even though the heuristic was demonstrated at Mhlume sugarcane milling area, it is recommended that other areas be considered for future research. The heuristic itself should continuously be updated with criteria, tools and other domain dimensions.
Vachellia sieberiana var. woodii a high-altitude encroacher: the effect of fire, frost, simulated grazing and altitude.
(2018) Russel, Jennifer Mary.; Tedder, Michelle Jennifer.
ABSTRACT There is increasing evidence that savannas and grasslands throughout the world are experiencing bush encroachment. The replacement of grassy biomes with woody biomes has serious consequences for net primary productivity. The grasslands of South Africa are not exempt from this phenomenon. Despite this, the drivers of the tree:grass dynamics are still robustly debated. In mesic and moist savannas and grasslands, the tree:grass balance appears to be maintained mainly through disturbance such as fire, frost and herbivory or a combination of disturbances. Other factors such as competition for resources may play a modifying role. High altitude grasslands are frequently within a climatic zone that would support trees, yet trees are absent. The answer as to what mechanism excludes trees from these grassy biomes continues to elude researchers. Very often low temperature is cited as a possible mechanism. Vachellia sieberiana var. woodii is a typical savanna tree which is absent from high altitudes. However, it has been encroaching into the grasslands along the escarpment of the Drakensberg, KwaZuluNatal, South Africa, over several decades, although is still excluded from the top of the escarpment. I acquired aerial photographs and satellite images covering the Van Reenen’s Pass area, north-western KwaZulu-Natal, dating from 1955 to 2015. These images confirmed that V. sieberiana was increasing in density along the escarpment, but that no V. sieberiana was present on top of the escarpment, despite the successful establishment of other tree species. The photographs and images also suggested that V. sieberiana was extending its range into higher altitudes. Because fire, frost and herbivory are generally thought to be the determinants of the structure of grasslands and savannas, I conducted field trials along the altitudinal gradient on Van Reenen’s Pass, investigating the effect of these determinants on the establishment of transplanted V. sieberiana saplings at three different altitudes. Competition for resources were briefly taken into consideration, although they were not the main thrust of the project: soil nutrients and root gaps. Soil moisture was not a concern as the area is what is defined as mesic. The transplanted saplings were smallest at the high-altitude site and largest at the low-altitude site after two growing seasons in the field. The response of the saplings to the various treatments was not consistent at the three sites. There was no response to the treatments at the highaltitude site; a significant response to fire, frost and simulated grazing at the mid-altitude sites; and a significant response to frost and simulated grazing at the low-altitude site.

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