Globally, low zinc (Zn) soils are widespread, but one of the largest expanses of such soils is in south west Australia (WA). Early Zn research in the region determined how much fertiliser Zn was required for profitable production of spring wheat (Triticium aestivum L.) and subterranean clover (Trifolium subterraneanum L), the major crop and pasture species at the time. The research showed that Zn sulfate and ZnO were equally effective Zn fertilisers, but ZnO was cheaper and so was widely used. The research indicated that in the year of application, depending on soil type, between 0.5-1.5 kg Zn/ha provided adequate Zn for the production of wheat and subterranean clover. The length of time that a single application of Zn fertiliser remains fully effective in maintaining the production of crops and pasture in future years (residual value; (RV)) had not been determined. This knowledge of the RV of Zn fertilisers is required for soils of WA. The experiments that measured the RV of fertiliser Zn for spring wheat and subterranean clover form the bulk of this thesis. The soils in the region were also initially acutely phosphorus (P) deficient requiring the application of fertiliser P for profitable production. Single superphosphate was the P fertiliser initially used. It was manufactured locally using phosphate rock imported from Nauru and Christmas Islands. This phosphate rock also contained much Zn, and the single superphosphate manufactured from it contained 400-600 mg Zn/kg. At amounts of application needed to provide adequate P, the Zn-contaminated superphosphate also supplied about 90 g Zn/ha. Therefore, early field experiments measured the RV of ZnO applied to soil when single superphosphate was applied annually at >150 kg/ha. In these experiments, the RV of Zn was measured when different amounts of fertiliser nitrogen (N) was applied. This was because it has recently been very profitable to apply fertiliser N to wheat crops, which greatly increased grain yields and so may have increased the demand for Zn, thereby probably decreasing the RV of the original ZnO application. In these experiments, there were many nil-Zn plots. In subsequent years, freshly-applied ZnO amounts were applied to measure the RV of the original ZnO treatments relative to the fresh Zn treatment. No Zn deficiency was detected for up to 23 years after applying ZnO while applying superphosphate at >150 kg/ha per year and for all amounts of N applied. Subsequently cheap imported DAP fertiliser was used for wheat crops instead of locally produced Zn-contaminated single superphosphate and urea. The imported DAP contained about 50 mg Zn/kg (1/12 that of single superphosphate). This new fertiliser strategy induced Zn deficiency in many wheat crops. This led to further field studies to determine the RV of ZnO fertiliser when DAP was applied. The experiments also included 2 Zn-contaminated single superphosphate treatments. In one, no ZnO was applied, and superphosphate was applied at >150 kg/ha per year to match the amount of P applied as DAP to the other treatments. The other treatment was the same, except 1.5 kg/ha Zn as ZnO was applied in the first year only. In subsequent years, freshly-applied ZnO amounts were applied to measure the RV of the original ZnO treatments relative to the fresh Zn treatment. Relative to freshly-applied Zn in each year, the RV of the original ZnO treatments decreased as the length of time that the Zn was in contact with soil increased. However, the rate of decline in the RV was also found to differ with soil type, and was affected by soil pH, clay and organic carbon content of soil, and in alkaline soils with the calcium carbonate content of soil. Parallel glasshouse studies measured the RV of Zn, as Zn sulfate, for wheat and subterranean clover, using many soils from WA and other Australian States. The glasshouse studies also showed that the rate of decline in the RV of the original Zn application varied markedly with soil type and was strongly influenced by soil pH, clay and organic carbon content of soil, and in the alkaline soils, the amount of calcium carbonate in soil. In the above studies, the RV of fertiliser Zn was measured relative to freshly-applied Zn using yield of plants (shoots and grain for wheat, shoots for clover), Zn content in shoots and grain, and soil test Zn using the ammonium oxalate and DTPA procedures. In addition, Zn concentration in young tissue and rest of shoots (glasshouse studies) and young tissue and whole shoots (field studies) was measured, and Zn concentration related to 90 % of the maximum yield (critical Zn in plant parts) was determined. The studies showed that the DTPA soil test procedure, together with soil pH, and clay and organic matter content of soil, was an accurate prognostic test for indicating when Zn deficiency was likely in the next clover or wheat crop. The study confirmed that young tissue (youngest fully expanded leaves) provided critical plant test values for diagnosing Zn deficiency in plants. The plant and soil tests for Zn are now used by commercial soil and tissue testing laboratories. When Zn deficiency was diagnosed early in field grown wheat, Zn sprays can be applied to the crop foliage to prevent or minimise decreases in grain yields at the end of the growing season. Zn sulfate and Zn chelate are the most widely used compounds. This thesis reports the results of a field study to compare the effectiveness of the two compounds when the spray was applied at two growth stages of wheat (Gs14; seedling growth and Gs24; tillering). In addition, Zn applied with the seed while sowing the wheat crop was also included. Zinc applied to the soil while sowing was the most effective treatment. Zn chelate was more effective as a spray than Zn sulfate when applied at the earlier growth stage, but Zn sulfate was cheaper, and both sprays were equally effective when applied at the later growth stage. Recently in the region, durum wheat (T. durum L.), narrow-leafed lupin (Lupinus angustifolius L.), yellow lupin (L. luteus L.), white lupin (L. albus L.), canola (Brassica napus L.), chickpea (Cicer arietinum L.), faba bean (Vicia faba L.) and lentil (Lens culinaris Medik) were all increasingly grown in rotation with spring wheat. Consequently, the Zn requirement of the new crops was compared with the Zn requirements of spring wheat. Species requiring less Zn than spring wheat to produce the same relative yield were faba bean, chickpea, albus lupin and canola; species requiring more Zn were lentil and durum wheat. Spreadsheet models were developed to determine when re-application of fertiliser Zn was required for low and high production systems. Relative to freshly-applied Zn, the rate of decline in the RV of Zn applied in a previous year varied depending on the amount of Zn applied, time the Zn was in contact with soil since application, properties of the soil (soil pH, % clay, % organic carbon, % free calcium carbonate), plant species, and the amount of Zn removed in harvested grain or hay. The thesis has culminated in a better understanding of Zn in the agricultural production systems of WA. The distribution and correction of Zn deficiency is now predictable for the many soil types and cropping systems of WA. Accurate identification of Zn deficiency for a range of crop and pasture species by plant analyses, typically the youngest mature leaf, is now possible for local conditions. With the calibration of the DTPA Zn soil test for soils of WA, particularly for wheat the major crop species grown in WA, prognosis of potential Zn deficiency can now be predicted before the appearance of Zn deficiency or loss in plant production.

Reliability-Cenetred Maintenance (RCM) is a well-known maintenance process developed in the aviation industry. It has yielded great success and hence was the process adapted to be used in the more industrial environments, such as the process developed by Moubray (1997) called RCM2. The RCM process is considered by many to be a very effective and comprehensive maintenance process that can, if implemented correctly, improve reliability and plant availability substantially. However, many maintenance practitioners and maintenance experts who have used RCM will tell you that it is an overcomplicated process and that it is difficult to implement. In many cases the process is abandoned and left incomplete due to the amount of resources required and the slow initial results delivered by the process. This dissertation investigates the reason for this and considers the viability of implementing the RCM process on an industrial level. The Hot Strip Mill (HSM) at the ArcelorMittal Vanderbijlpark plant was used as a case study. The viability of using RCM to improve the HSM maintenance practices was investigated. A suggested maintenance improvement plan was developed that is more suitable for the HSM maintenance environment and culture. / MSc (Development and Management Engineering), North-West University, Potchefstroom Campus, 2015

Reliability-Cenetred Maintenance (RCM) is a well-known maintenance process developed in the aviation industry. It has yielded great success and hence was the process adapted to be used in the more industrial environments, such as the process developed by Moubray (1997) called RCM2. The RCM process is considered by many to be a very effective and comprehensive maintenance process that can, if implemented correctly, improve reliability and plant availability substantially. However, many maintenance practitioners and maintenance experts who have used RCM will tell you that it is an overcomplicated process and that it is difficult to implement. In many cases the process is abandoned and left incomplete due to the amount of resources required and the slow initial results delivered by the process. This dissertation investigates the reason for this and considers the viability of implementing the RCM process on an industrial level. The Hot Strip Mill (HSM) at the ArcelorMittal Vanderbijlpark plant was used as a case study. The viability of using RCM to improve the HSM maintenance practices was investigated. A suggested maintenance improvement plan was developed that is more suitable for the HSM maintenance environment and culture. / MSc (Development and Management Engineering), North-West University, Potchefstroom Campus, 2015

<p>Manatees (Mammalia: Sirenia), along with the closely related dugongs, are the only herbivorous marine mammals. Manatees consume a wide variety of vascular plants and algae in both marine and freshwater habitats. However, little is known about what characteristics influence diet and food selectivity, especially in freshwater habitats, which represent a large portion of the available habitat for the endangered Antillean manatee, <italic>Trichechus manatus manatus</italic>, in Central and South America. Understanding foraging ecology is an important element of effective conservation strategies.</p><p>This dissertation investigated various aspects of the foraging ecology of the Antillean manatee in a freshwater habitat, specifically: 1) how plant availability (i.e. species richness, diversity, and abundance) varied seasonally with changes in water depths, 2) manatee food selectivity from a representative set of plant species from that freshwater habitat, and 3) the relationship of plant nutritive compounds and availability with manatee food selectivity. In addition, this dissertation describes the multiple uses of sonar technology for studying manatees and habitat characteristics in freshwater.</p><p>Plant availability to manatees was evaluated by conducting monthly plant surveys from July 2010-July 2011 in four contact lakes in the wetlands of Tabasco, Mexico. Manatee food selectivity was examined by conducting food selection experiments on a wild adult manatee during the low water season with 54 plant species representing 25+ genera. The nutritive components (i.e. crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF), hemicellulose (HC), and ash) and plant availability values for selected and non-selected plants species were evaluated to determine their relationship with manatee food selectivity. The applicability of using side-scan sonar for manatee research was tested in various freshwater and estuarine habitats in Honduras, Costa Rica, Panama, and the wetlands of Tabasco, Mexico between 2006-2011.</p><p>The major findings of this dissertation are as follows. Plant species richness, diversity, and abundance were greatest during the rising water season (July-August) and lowest during the low water season (March-June). No plants were available in April-June, which represented the majority of the low water season. The wild manatee</p><p>selected 27 (11+ genera) of the 54 species examined during the feeding experiments. Of the plant characteristics tested (i.e. nutritive components and plant availability), only digestible fiber (HC) was significantly related to manatee food selection, with manatees</p><p>selecting plants with higher HC content. Four unique applications were identified for the use of side-scan sonar to facilitate manatee research in freshwater habitats: 1) confirmation of visual sightings and determination of group size, 2) determination of mother-calf pairs, 3) habitat characterization, and 4) assisting manatee captures.</p><p>Results from this study reveal that manatees living in the freshwater wetlands of Tabasco, Mexico have to cope with a highly seasonal availability of plants and that while manatees consume plants from a wide variety of genera, they are highly selective. Unlike other herbivorous mammals, manatee food selectivity was not influenced by CP, NDF, or ADF, but rather by digestible fiber. A unique suit of anatomical and physiological characteristics suggests that manatees may be fiber digestion specialists. Both seasonal plant availability and the manatee's large dietary breadth must be considered when developing 1) conservation strategies for wild manatees in freshwater habitats and 2) protocols for captive rehabilitation of orphaned and stranded manatees that will be reintroduced into the wild.</p> / Dissertation

An injection technique, in which undisturbed soil cores are labelled with ³²P to study dissolution of phosphate fertilisers in the soil, was evaluated in field and glasshouse trials. When ³²P was injected between 0-150 mm depths of the undisturbed soil columns and fertilisers applied at the surface, the amounts of fertiliser P dissolved, as measured by the increases in the exchangeable P pools, were overestimated. Three possible reasons were suggested: (i) the interaction between surface-applied fertiliser, ³²P injected through the whole soil column, and the vertical decline in root density, (ii) the decline of specific activity in the exchangeable P pool due to losses of ³²P to nonexchangeable P pools and continuous addition of P from fertiliser dissolution, and (iii) non-uniform distribution of ³²P vis-a-vis ³¹P phosphate. The injection technique may be employed to assess the effectiveness of phosphate fertilisers by introducing a concept, the fertiliser equivalent (FE). The FE is a measure of the amounts of soil exchangeable P that the fertilisers are equivalent to in supplying P to plants, when applied at the specific location. Soluble single superphosphate (SSP) applied at the surface of undisturbed grassland soil cores (Tekapo fine sandy loam), was much more effective than surface-applied unground North Carolina phosphate rock (NCPR) and 30% acidulated NCPR with phosphoric acid (NCPAPR) within the 56 day period of plant growth. An isotopic dilution method, based on tracer kinetic theory, was developed to study the rates of dissolution (F in) and retention (F out) of phosphate fertilisers in the soil in growth chamber experiments. The estimation of F in and F out required labelling of the soils with carrier-free ³²P and determination of the corresponding values of the specific activities of the exchangeable P pools, SA₁ and SA₂, and the sizes of the exchangeable P pools, Q₁ and Q₂, at times t₁ and t₂. Most of the phosphate in the monocalcium phosphate (MCP) solution entered the exchangeable P pool immediately after addition to the soils (Tekapo fine sandy loam and Craigieburn silt loam), and there was little further phosphate input. With increasing periods of incubation, the phosphate was quickly transformed to less rapidly exchangeable forms. In the soils treated with ground North Carolina phosphate rock (<150 µm, NCPR) or partially acidulated (30%) NCPR with phosphoric acid (NCPAPR), the initial exchangeable P pools were not as large as those in the soils treated with MCP, but were maintained at relatively stable concentrations for extended periods, due to the continuous dissolution of PR materials and to lower rates of pretention. An increase in P-retention caused a slight rise in the rate of PR dissolution, but also a rise in the rate of P-retention by the soil. The rate of dissolution was higher at a lower application rate in relative terms, but smaller in absolute terms. The trends in the changes of plant-available P in the soils, measured by the water extractable P, Bray I P and Olsen P, correspond to those predicted by the F in and F out values. The average rates of dissolution between 1-50 and 50-111 days estimated by the F in, however, were higher than those estimated by extractions with 0.5 M NaOH followed by 1 M HCl, and with 0.5 M BaCl₂/TEA. This is partly because the Fin values reflect a plant growth effect on PR dissolution. The relative agronomic effectiveness of NCPR and NCPAPR with respect to MCP was higher after 50 and 111 days of incubation than after 1 day. The F in values were included in all the two-variable models constructed by stepwise regression to describe the relationship between plant P uptake and soil measurements. The amounts of variation in plant P uptake accounted for by the regression model was significantly improved by including F in in the model. This indicates the importance of fertiliser dissolution rates in affecting soil P supply, when phosphate fertilisers differing in solubility are applied.