Agricultural Engineering

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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.
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.
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.
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.
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.
Process and modelling studies in forest hydrology.
(1995) Summerton, Mark John.; Schulze, Roland Edgar.
The demand for timber products in South Africa, and consequently afforestation, is increasing. There exists, however, abundant experimental evidence that trees utilise more soil water than other dryland crops. Because water is limited in South Africa, decision makers therefore currently face the challenge of determining a socially, and economically acceptable afforestation management plan to enable the reconciliation of increased timber demand with scarce water supply. This challenge, and the subsequent decisions that need to be made, may be accomplished by making use of suitable simulation models to predict the impacts of the forest hydrological system on water resources. Currently, these impacts are assessed through an Afforestation Permit System (APS) which is based on a model now acknowledged to have become outdated. In this dissertation an enhanced ACRU Forest Decision Support System (FDSS), now called the ACRU Forest model, is developed and proposed as a tool for modelling forest hydrological impacts on water resources. Research for this study included a literature survey, fieldwork at two locations, viz. at forest irrigation trials at Mkuze in northern KwaZulu-Natal, and at forest site preparation trials near Ugie in the Eastern Cape, as well as the evaluation, for purposes of model development, of a series of workshops. Results from the fieldwork experiments show that large tree water use potentials are possible if water is not limiting, although a water supply threshold exists at about 1400mm.annum-1, above which diminishing growth returns occur. Furthermore, trees display improved growth on more intensive forest site preparations, but at the expense of higher water usage rates. A series of workshops which had as the main objective the extraction of expert knowledge by stimulating responses to prepared questions and by constructive discussion on relative issues pertaining to forest hydrological modelling, yielded valuable information. This information, together with that gleaned from the literature, the fieldwork and a new Quaternary catchment database for South Africa, was used to develop the ACRU Forest model. The PC-based ACRU Forest model has the potential to aid decision makers by providing an initial indication of the impacts of afforestation on water resources, within a matter of minutes. An example of the model's application is used to demonstrate its operation, relative accuracy and its potential benefits in simulating hydrological responses to afforestation.
Issues pertaining to cane supply reliability and stockpiling at the Umfolozi sugar mill - model development and application.
(2011) Boote, Gordon L. N.; Bezuidenhout, Carel Nicolaas.; Lyne, Peter William Liversedge.
The co-owned Umfolozi Mill area has developed as an integrated supply chain. Cane supply reliability was identified as a potential area for productivity improvement at Umfolozi. It is important that the cane supply to a sugar mill arrives at a steady and reliable rate. A reliable cane supply ensures that the mill can operate at an optimum efficiency. Sugarcane supply reliability depends on how the mill area adapts to unforeseeable changes in the supply chain. An important aspect to this is the weather and how it affects the harvesting regimes. The sugarcane supply chain at Umfolozi is divided into two branches, road transport and tram transport. The trams account for 70 % of the cane delivered to the mill and the can is sourced from a climatically homogenous region. In the occurrence of a rainfall event of above 5 mm, infield harvesting cannot take place on the Umfolozi Flats; hence 70 % of the mill‟s supply is halted for one or more days. To address the problem, a stochastic model was created to simulate the effectiveness of an enlarged cane stockpile if it were maintained on the current tram sidings outside the mill and were crushed when wet weather prevented further harvesting. The stockpile was simulated on a first-in first-out principle and was able to supply the mill with enough cane to continue running for 24 hours. The model was then used to conduct a series of Monte Carlo simulations on which sensitivity analyses and economic feasibility assessments were carried out. Results show that the stockpile was effective in reducing the length of milling season and the number of no-cane stops. However, on further analysis into the implications of creating a stockpile it was found that 1% recoverable value (RV) was lost during the 24-hours that the cane is stored outside the mill. The loss in revenue as a result of the RV reduction had a negative impact on any savings created with the implementation of the stockpile. This result made apparent the negative impact of deterioration to the whole supply chain. Further research is required to determine more accurately the rate of deterioration, and therefore, quantify more accurately the losses that occur in the supply chain. A significant outcome of the study was the development of a mechanistic tool which drove decision making at Umfolozi Sugar Mill. It lead to the development of the modelling framework LOMZI, a simulations based framework which places more emphasis on environmental factors and risks.
The preparation and novel application of diphosphorus xanthene family ligands in homogeneous catalysis.
(2011) Marimuthu, Thashree.; Friedrich, Holger Bernhard.
Abstract available in print version.
Assessing the performance of smallholder irrigation in South Africa and opportunities for deriving best management practices.
(2012) Gomo, Taziva.; Senzanje, Aidan.
South Africa is a water scarce country. With the increasing demand of water from other users, irrigation, as the largest water user, has to find ways to produce more per drop and meet the food demands of the growing population. Enhancing the performance of smallholder irrigation schemes (SHI) is one way of saving water since they are fast becoming the largest water users in South Africa and the world over. Performance in the smallholder sub-sector is reportedly below the expectations of stakeholders. However, performance in smallholder irrigation schemes is multi-dimensional and can be looked at from different perspectives. This study assessed the technical performance of the Mooi River Irrigation Scheme (MRIS) from the technical managers` and the farmers` points of view and integrated them into one to derive a comprehensive set of best management practices (BMPs) for the scheme. This was done acknowledging that the farmer is now the water manager in line with Participatory Irrigation Management (PIM) and Irrigation Management Transfer (IMT). Three performance indicators related to water supply and delivery: conveyance efficiency, dependability of irrigation intervals between water applications and relative irrigation supply, and two agricultural performance indicators namely, output per unit irrigation supply and output per unit water consumed, were assessed during the spring and summer of the 2010/11 season. The field measurement method was used for the assessment of these indicators as opposed to the faster and more encompassing remote sensing method, due to resource constraints. The Velocity-area method was used to measure flow-rates in canals and crop water demands were estimated from FAO Cropwat 8.0 and Aquacrop 3.1. The results show an overall scheme conveyance efficiency of 86.4%, a maximum dependability of irrigation intervals between water applications of 2.57 in spring and a scheme relative irrigation supply of 1.48. Agricultural performance indicators, output per unit irrigation supply and water productivity per unit crop evapotranspiration (ET), were found to be 0.64 kg/m3 and 5.37 kg/m3 on average for cabbage, respectively. Farmers` satisfaction with taking an irrigation service can be used as a measure of the scheme`s performance. A questionnaire was administered among farmers to gather their views on the performance and to determine the factors that significantly influence their satisfaction status with taking the irrigation service at MRIS. Information collected from the questionnaire include age, gender, irrigation training, timeliness of water delivery, water distribution among the blocks, farming experience, farmer involvement in inspection of irrigation infrastructure and maintenance, among others. Farmers` were also asked for suggestions on improving the performance of their scheme. Their responses were analysed using a multinomial logit model. Results showed that 57% of the farmers are satisfied with using the irrigation service at MRIS, 30% are not satisfied, while 13% are neutral. Eight factors were found to be statistically significant in influencing the farmers` satisfaction status namely: location with respect to the water diversion point, location within a block from the main canal, age of the farmer, education level attained by the farmer, farming experience, the number of plots a farmer owns, fairness of water distribution across the blocks and the number of days a farmer accesses water The technical performance indicators assessed and the suggestions from the farmers on the way to improve performance of MRIS allowed the selection of the BMPs for the scheme. A set of seven BMPs based on farmer suggestions was derived. BMPs used as a guideline. The farmers were also tasked with the ranking of the derived BMPs according to their preference. The collected data was then ranked through an Analytic Hierarchy Process (AHP). The results show that establishment of and adherence to an irrigation schedule was the most preferred BMP by the farmers, while volumetric measurement of irrigation water used by each block was the least preferred. This study concludes that the performance of MRIS is comparable to other schemes and that farmers are aware of the problems bedevilling their scheme. It is also concluded that the performance of the scheme meets the farmers`, the key stakeholders, expectations and that irrigation scheduling is the most preferred BMP. The study recommends that farmers be more involved in performance assessments and management of their schemes. It is crucial to ensure that the recommended BMPs are acceptable to the farmers in the scheme. The best way to achieve this is by allowing farmers to participate in policy formulation and decision making.
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.
The development and evaluation of a radio frequency identification based cattle handling system.
(2013) Mutenje, Tendai Justin.; Smithers, Jeffrey Colin.; Simalenga, T. E.
Manual cattle handling systems are widely used in South Africa. A literature review and consultations were conducted with both producers and equipment manufactures, to assess the advantages and disadvantages of various cattle handling systems with the objective of developing a more efficient system that incorporates automation, electronics and Radio Frequency Identification (RFID) technology. In this study an automated, selective sorting (RFID) based cattle handling system was developed and assessed as an alternative to the widely adopted conventional manual management system practiced in South Africa. The system is still under research and not yet available on the market. This document describes the research and development process undertaken which included planning, literature review, consultation, design, fabrication, evaluation and discussions. The RFID based system developed consists of manual, semi- and fully automated components in the form of a neck-body clamp with through access, flow control double split gates and a weigh-identification-sort system. For the ease of comparison the system was developed with a manual by-pass as a control to compare the automated and manual systems in terms of establishment cost, handling duration including identification, weighing and sorting, and operator and animal stress levels which impact on business profitability and system efficiency. Both the manual by-pass and automated RFID-based systems were evaluated. The automated system resulted in reduced handling duration, operational costs and handling stress on both operator and the animal whilst enabling selective automated sorting. The infrastructure was designed to have a capacity to handle 500 animals per day with 5 handlers and a capital investment of R200 000 was required with an operational cost of R25 000 per month. After incorporating RFID, electronics and automation of the system it was established that, on average, cattle handling duration was reduced by 63%, incorrect sorting was reduced by 5.5%, man hours were reduced by 70% with 23% and 14% less fatigue and stress levels to the handler and the animals respectively, whilst achieving efficient selective sorting. A cost benefit analysis was undertaken for both systems with the aim of assessing and determining the most profitable system. An assumption was made that the cash flow pattern remains uniform for both systems over the entire evaluation period. This revealed that the introduction of RFID based technology as an alternative to a manual based system results in an increase in business profitability by 20% and shorten the payback period by 5 years. Although there is still need to further investigate the performance parameters under different environments, it can be concluded that the introduction of RFID, electronics and automation improves the overall system technical efficiency by 32% whilst enabling efficient selective handling.
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.
Modelling sugarcane quality in the context of mill scale supply chain logistics.
(2014) Jenkins, Edwin Peter Garland.; Bezuidenhout, Carel Nicolaas.; Ortmann, Gerald Friedel.
The length of milling season (LOMS) refers to the length and timing of sugarcane crushing operations at a sugar mill. LOMS is central to the competitiveness and profitability of any sugar mill supply area (MSA). Conflicting interests between supply chain stakeholders can make adjusting the LOMS difficult. The LOMS should take into account weather conditions, cane quality, milling capacity, supply chain capabilities and other interrelated issues, such as agronomics. Previous LOMS models in South Africa were developed over a decade ago and there was scope to improve the calculation of risks by using a stochastic modelling approach. Recently, a stochastic model named LOMZI was developed to evaluate stockpiling options at Umfolozi. In this study, LOMZI was adapted and expanded to allow the LOMS for any MSA in South Africa to be investigated. However, mill area specific applications of the updated model fell outside the scope of this study. As it currently stands, LOMZI simulates a sugarcane supply chain from the point where sugarcane is cut, up to delivery at the mill. During the process of adapting LOMZI, the simulation of sugarcane quality was identified as an important area for improvement in the model and this became the focus of the study. A predictive MSA scale cane quality model was developed, based on recent weather conditions and a mechanistic understanding of sugarcane quality. The quality model was developed to simulate the daily average brix %, pol % and fibre % of sugarcane delivered to the mill. The preceding 11 weeks’ rainfall and temperature values were used to predict cane quality. A total of 98 mill-specific coefficients were calibrated from historic milling data and, for model demonstration purposes, the quality model was applied at two mills, namely Sezela and Umfolozi. Independent verifications yielded R2 values between 0.56 and 0.74. A useful method to estimate the average burn/cut to crush delay for a MSA was also identified. The quality model has been successfully integrated with LOMZI. Future work is envisaged to expand LOMZI and to model the operations of sugar mills and the RV cane payment system.
The development and assessment of a direct energy calculator for use in sugarcane production.
(2014) Boote, Darran N.; Smithers, Jeffrey Colin.; Lyne, Peter William Liversedge.; Van Antwerpen, Rianto.
The rising cost of energy coupled with an increasing awareness of Greenhouse Gas (GHG) emissions has led to a concerted effort to reduce fossil fuel Energy Use (EU) in all sectors. Sugarcane production in South Africa is dependent on fossil fuel to provide a source of energy for production. To remain commercially and environmentally sustainable, measures need to be taken to reduce EU and increase EU efficiencies of on-farm operations. The first step toward realising this is to identify and quantify energy inputs. Following on from this, total GHG emissions, also known as carbon footprint, can be estimated. The primary objective of this research is to develop an energy calculator to estimate EU in sugarcane production in South Africa. The results generated by the calculator highlight areas of high energy intensity and low energy efficiencies at three different levels of detail. Based on these results, changes in management practices and technological improvements can be made to reduce EU and carbon footprint. Case studies were used to test the functionality of the calculator. Results from the case studies show that, in irrigated sugarcane production, the harvest and transport process together with irrigation account for a majority of the total on-farm EU. For one of the case studies, an estimated 20 % saving in the total on-farm EU was identified and can be achieved if appropriate technology is adopted in irrigation practices. Less significant energy savings were realised when in-field tractor operations were optimised for best tractor-implement matching. It is envisaged that the energy calculator will help farmers minimise on-farm EU and subsequently reduce input costs and carbon footprint. It will also provide a valuable tool for researchers to benchmark and profile EU in sugarcane production in South Africa. Research focussed on the sustainable production of sugar, from the agricultural to milling phase is of high priority at present. The quantification of on-farm EU in sugarcane production will form a critical component of such research.
Comparative analysis of two greenhouse microclimates in the sub-humid climate of South Africa.
(2014) Thipe, Ellen Letsogile.; Workneh, Tilahun Seyoum.; Odindo, Alfred Oduor.; Laing, Mark Delmege.
Development of small-scale greenhouse facilities that are suitable for the southern African agro-climatic conditions is one of the options that can be adopted to help alleviate food insecurity and malnutrition in Southern African countries. A comparative study was undertaken to analyse the temperature and relative humidity (RH) of two types of greenhouse tunnels, namely, the fan-pad evaporatively-cooled (FPVT) and the open-ended naturally-ventilated tunnels (NVT). The effect of the microclimates on crop growth, yield and quality, using tomatoes during the summer months and lettuce in winter, were also investigated. The effects of the integrated agro-technologies involving greenhouse microclimate and storage conditions on the postharvest quality of four tomato cultivars was also studied. The daytime temperature was lower in the FPVT than in the NVT during both summer and winter periods. Night-time temperatures were not significantly (P>0.05) different. The RH was higher in the FPVT than in the NVT, both during the day and at night. There was also a marked vertical and horizontal variation of temperature and relative humidity. Tomato vegetative growth was significantly (P<0.05) higher in the FPVT, but there were no significant (P>0.05) differences in the total yield and the total marketable yield of tomatoes grown in the FPVT and the NVT. However, the total yield was 24% higher in the NVT, but the total marketable yield was 8.3% higher in the FPVT. Highly significant (P<0.01) cultivar differences were observed, with Bona performing the best in terms of total yield and total marketable yield under both NVT and FPVT microclimates. During winter, there were no significant (P>0.05) differences in the growth and yield of lettuce crops resulting from the effect of the microclimate, although there was a higher incidence (by 26.9%) of leaf tip-burn in the FPVT. Between the two lettuce cultivars, growth was faster and the yield was 11.5% higher for Ballerina than for Nadine. However, Ballerina also had 24 to 29.6% more leaf tip-burnt leaves than Nadine. The integrated agro-technology study involving pre-harvest and postharvest treatments, which included the effect of greenhouse microclimate and postharvest storage environmental conditions on the texture, colour, TSS and pH of the four tomato cultivars, had significant (P>0.05) effects. NVT-grown tomatoes had and retained a firmer texture (by 7.4%) for a longer period, had a higher TSS value (by 10.3%), but a more rapid colour change, from mature-green to red-ripe, than FPVT tomatoes. Among the four tomato cultivars, Bona was the least firm and changed colour from green to red more rapidly, but it had the highest TSS and acidity than of the other three cultivars. With cold storage conditions at 13°C and 85% RH, the firmness of Bona was improved by 24.1% and the colour changes were reduced by 18.6%, compared to those under ambient air conditions (23± 2°C and 52± 4% RH). The cultivars Star 9037 and Star 9009 had the highest firmness and changed colour the least, but had the lowest TSS and highest pH values. This study has provided information about the microclimate of two types of greenhouses and their performance, in terms of the effects on growth, yield and quality of four tomato cultivars in summer and two lettuce cultivars in winter. The microclimate in the FPVT encouraged vegetative growth and improved the quality of the tomatoes. In the NVT, although the total yields were higher, the higher temperatures and insect/pests reduced the quality of the tomatoes. In winter, although the daytime temperatures were higher in the NVT, lettuce growth was not negatively affected, whereas in the FPVT, high humidity resulted in lower quality lettuce. The study also provided information on the integrated agro-technologies, involving greenhouse microclimate and postharvest storage environmental conditions on the postharvest quality attributes of tomatoes available on the South African market. NVT-grown tomatoes need cold postharvest storage, to reduce the ripening, in terms of colour, whereas FPVT grown tomatoes need cold postharvest storage conditions, in order to maintain a firmer texture for a longer period. It has also shown that the selection of the most suitable cultivar is important for profitable cultivation of vegetable crops in greenhouses. The study has further shown that small-scale naturally-ventilated greenhouses can be used for commercially-oriented agriculture to produce crops, with the aim to reduce poverty, create employment and address malnutrition. In addition, the study has shown that there is a need for further research aimed at reducing the daytime heat load of the greenhouses during the summer months, and the night-time heat loss during winter and a cost-benefit analysis, to establish the cost of production associated with the two tunnels. Furthermore, greenhouse microclimate research can be extended to the other South African climatic regions, to provide extensive information about the performance of these facilities and their effects on other greenhouse crops such as peppers and cucumbers.
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.
Infrared drying of biltong : effect of pre-treatment and drying conditions on the drying characteristics and product quality.
(2014) Cherono, Kipchumba.; Mwithiga, Gikuru.; Workneh, Tilahun Seyoum.
In this study, the drying kinetics of biltong was investigated under infrared and convective drying systems, with two product pre-treatment conditions namely, slice thickness and marinating duration. The effect of these treatments on the quality and microbiological food safety of biltong was investigated. In addition, the study sought to establish and compare the energy efficiencies of the infrared drying systems under investigation. The drying of biltong was conducted under two infrared drying conditions (2.5 μm and 3.5 μm peak wavelengths) and a convective drying condition that mimicked conventional and commercial drying conditions at a temperature of 25°C and 60% relative humidity. The two infrared heating systems were set so that they had the same intensity of 4777 W.mˉ² at the product surface, but different peak wavelengths (2.5 μm and 3.5 μm). The marinated products were dried from a moisture content of 73.99% ± 1.46% wet basis (wb) to the commercial quality requirement of 20% ± 1% wb. Samples had a product thickness of 5, 10 or 15 mm, and had been marinated for durations of 6, 12 or 24 hours prior to drying. The experiments were arranged in a complete randomized block design. The drying rate, product temperature, quality attributes, such as colour, texture, shrinkage, rehydration, as well as total viable bacterial counts were measured, along with the infrared power consumption during the drying process. It was observed that the infrared heater with a peak wavelength of 2.5 μm dried the products faster, when compared to the one with a peak wavelength of 3.5 μm at all times, even when the infrared intensity of both heaters on the products was the same. The convective drying system recorded lower drying rates and longer drying durations compared to the infrared heating systems. Increasing product thicknesses increased the drying times and reduced the drying rates for samples dried under the 2.5 μm peak infrared heater and the convective drying system. Increasing the duration of marinating, reduced the drying rates for samples dried under the convective air dryer and increased the drying rates for samples that were dried under the 2.5 μm peak infrared heater. The 3.5 μm peak infrared heater recorded varied results, but generally had the 10 mm thick and 12-hour marinated samples having higher drying rates for all samples dried under this system. The drying system used significantly (p≤0.05) affected the drying times, while the pre-treatment conditions had no significant (p≥0.05) effect on the drying times. The core temperature increased with decreasing product thicknesses and increasing marinating duration for the 2.5 μm peak infrared heater. However, the 3.5 μm peak infrared heater product core temperature did not follow the same trend. This system recorded lower specific energy consumption (SEC) values, compared to the 2.5 μm peak infrared heater. Out of the five drying models tested, the drying kinetics of biltong was best described by the approximation of diffusion model (ADM) on the basis of the model’s high coefficient of determination (R²) and low root mean square error (RMSE) values. The sample lightness (L*) of dried samples was significantly (p≤0.05) influenced by the drying system. The convective air drying system recorded lower total colour difference (ΔE) values compared to the infrared systems. The L* a* b* colour parameters decreased after marinating fresh beef slices, and decreased even further after the drying process. Textural analysis showed lower hardness and puncture values for samples dried under the 2.5 μm peak infrared heater compared to the other drying systems. Samples dried under the 3.5 μm peak infrared heater recorded the highest shrinkage coefficient and rehydration rates. The three drying systems achieved at least a 2-log reduction in the total viable bacterial count, with the 2.5 μm peak infrared heater having the lowest most probable number (MPN) count of 7,020. The infrared drying systems produced biltong that had acceptable plate counts of E-coli less than 10² CFU.g⁻¹. However, the convective air drying system did not meet this acceptability threshold for the safe consumption of biltong. The samples that were dried under the 2.5 μm peak infrared heater recorded high drying rates, good microbiological safety and textural attributes compared to the convective and 3.5 μm peak infrared drying systems. However, this system had consumed more energy compared to the 3.5 μm peak infrared heater that produced biltong with superior shrinkage coefficient and rehydration characteristics as well as colour attributes that closely compared to those of samples dried under the convective air drying system. The study recommends both the 2.5 and 3.5 μm peak infrared heaters for the best texture of biltong, improved drying characteristics and enhanced microbial food safety of the product.
Evaluation of systems to harvest, process and transport sugarcane biomass.
(2015) Rees, Bryan.; Smithers, Jeffrey Colin.; Lyne, Peter William Liversedge.; Van Antwerpen, Rianto.
One of the problems facing the world today is the fact that fossil fuel reserves are declining and, as a result, petrol and diesel costs are increasing. For the past century, fossil fuels have been the primary fuel source for most countries around the world and this has had an impact on the environment. This has resulted in the South African government, in line with international trends, investigating alternative energy sources to supplement and meet an increasing demand for energy. Biomass (e.g. leaves of sugarcane, referred to as sugarcane residue) is receiving increasing attention, as it is a sustainable and environmentally-friendly source of renewable energy. In South Africa, the majority of the sugar industry manually harvests burnt sugarcane. Thus, innovative residue recovery systems need to be developed to accommodate the manual harvesting of green/unburnt sugarcane. In this document, sugarcane residue refers to green/wet and brown/dry leaves, tops and green leaves constitute green residue, brown leaves constitute dry residue, and bagasse is the pulp left after the juice has been extracted from the sugarcane stalks. The name ‘residue recovery route’ encompasses both green and dry residue as, although ideally dry residue is collected, some residue recovery routes collect green residue in addition to dry residue. The objectives of this study are: (i) to assess the potential energy available from dry sugarcane residue, taking into account the benefits of leaving a residue blanket in the field, and (ii) to investigate the harvesting systems, energy and costs required to recover the residue and deliver it to a mill for both new production and harvesting systems and systems currently used in South Africa, which range from manual harvesting to fully mechanised systems. Current residue recovery methods, as well as potential methods which are still under development, are reviewed in this document. A costing model has been adopted and further developed, with the objective of estimating the costs incurred by residue collection and transport. The different residue recovery routes, which were identified in the literature review, were incorporated into the model. These routes include different methods of harvesting, residue separation infield or at the mill, the method of residue collection, residue processing and the transportation of the residue. Processing to increase the bulk density of the sugarcane residue prior to transport has been considered in this study, as its low bulk density has been identified as a critical issue in other studies. By processing the residue, the energy density and bulk density of the residue can be increased, which, in turn, improves the transport efficiency. Problems encountered when modelling residue processing included estimating the capital cost requirements, as well as the maintenance and operating costs, for each processing plant. The model was applied to two case studies, in order to compare the costs for each individual residue recovery route. This enabled the lowest cost and appropriate residue recovery route to be identified for the case studies. The cost per unit energy was used to compare the cost of the residue recovery to the cost of coal at the mill, which is required to determine whether sugarcane residue is an economically-viable source of renewable energy. Based on the assumptions made for the lowest cost routes which were identified, it was found that the cost of the residue recovery i.e. the cost of the residue, was less than that of coal and, thus, these routes are potentially economically beneficial for the mill.
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.
Assessment of the performance of small-scale water infrastructure (SWI) for multiple uses in Nebo Plateau, Sekhukhune District, South Africa.
(2015) Sambo, Doctor Calvin.; Senzanje, Aidan.
South Africa is ranked the 30th driest country in the world and water is regarded as a scarce resource in the country. Limited availability of good quality water has resulted in urban areas receiving more water at the expense of rural areas. This is due to the fact that urban areas have a more reliable and well-maintained water infrastructure, while rural communities use unreliable and dysfunctional small-scale water infrastructure (SWI). Enhancing the performance of SWI (which are technical hardware used by rural communities to supply water for their day-to-day activities such as domestic, irrigation and rural development) used by the rural communities can enhance their rural livelihoods. The SWIs are designed and operated either as single use systems (SUS) that cater for only one water-use or multiple water systems (MUS) that cater for more than one water-use. These SWI are usually dysfunctional due to a number of reasons. Investment into SWI development, operation and maintenance (O&M), rehabilitation and modernization is limited by the lack of knowledge of the types of SWI in a given area and their functional status. This study sought to assess the performance of SWI in Nebo Plateau, Limpopo Province, South Africa by (a) identifying their types, distribution, ownership, water-use and status using a survey tool administered to the rural communities, (b) assessing their condition using modified technical and risk of failure evaluation tool, (c) investigating their causes of failure using a qualitative research approach and network analysis, and then (d) propose best management practices (BMPs) that are specific to the study area. The study found 202 SWI, which comprised of the following: unequipped boreholes (59%), equipped boreholes (hand pumps (10%), electric-driven pumps (6%), diesel-driven pumps (1%) and windmills (4%)) and small reservoirs (11%). The overall water uses were 65% SUS, 22% MUS and 13% other. The government owned 54% of the SWI, communities owned 22%, private sector owned 11%, and schools owned 2%. The government was responsible for the maintenance of 49% of the SWI. It was found that 71% of the identified SWI were nonfunctional It was found that windmills had minor defects and met rural community needs above satisfactory level. On the other hand, small reservoirs and hand pumps required major maintenance and benefited the rural communities below the minimum level. The major causes of failure were found to be lack of proper operation and maintenance (O & M), lack of O & M strategies, inadequate funds, no monitoring strategies, lack of technical skills at municipality and community level, and lack of strong leadership from the policy regulating institutions, Water Service Authority, water service provider and rural communities. It was proposed that for improved water supply to the rural communities of Nebo Plateau, there was a need to decentralize the current District municipality water service providers (WSP), establish Village Water Committees (VWC) in the rural communities, link policy with technology used, consider the effects of environment on technology, ensure availability of spare parts locally, provide technical training for both WSP and rural communities, and allocate funds for operation and management of the SWI. The study concludes that there are different SWI used by the rural communities in the study area and operated as SUS and MUS. The rural communities used water mainly for domestic and irrigation of back yard gardens. Water from small reservoirs was mainly used for livestock watering. The government owned most of the SWI and were also responsible for their maintenance. Most SWI assessed during this study were non-functional thus depriving rural communities of improved standards of living. The factors that caused the poor performance of SWI were interdependent and resulted mainly from the lack of strong institutional capabilities. The proposed BMPs were suitable for the rural communities of Nebo Plateau. It is, therefore, recommended that stakeholders involved in SWI management use the information on the status of SWI presented in this document to address areas with poor performing SWI and adopt or apply the proposed BMPs to improve their performance.

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