Orientador: Marco Antonio Martin Biaggioni / Banca: Enzo Dal Pai / Banca: Magnun Antonio Penariol da Silva / Banca: Erico Tadao Teramoto / Banca: João Alberto Borges de Araujo / Resumo: A secagem é considerada a etapa de maior gasto energético na produção de grãos, sendo normalmente efetuada com a queima de biomassa, como a lenha, por exemplo. Do ponto de vista financeiro, a secagem de grãos continua sendo dispendiosa e inviável para pequenos agricultores. O objetivo deste trabalho foi projetar, construir e avaliar a viabilidade técnica e econômica de um coletor solar de tubo de polietileno em espiral, destinado à secagem de grãos de milho, em leito fixo, para pequenas propriedades rurais. O coletor foi testado em três condições distintas: sem cobertura, com cobertura de plástico de estufa e com cobertura de vidro. A área do coletor é 4,18 m2 . A caracterização do coletor foi feita com o levantamento do rendimento térmico, sua curva de eficiência e da perda de carga no coletor. O desempenho do sistema de secagem foi avaliado com a determinação do consumo específico de energia, tempo de secagem, temperatura da massa de grãos e plenum e custo de secagem. Foi realizada também uma simulação do tempo e custo de secagem em comparação com secador comercial. O coletor com cobertura de vidro obteve os melhores resultados com temperatura média na saída do coletor de 69,87°C, entrada de 35°C e eficiência térmica de 19%. Os coeficientes de absortividade e perdas registrados foram FR(τα)=0,150, FRUL=1,101, respectivamente. O vidro proporcionou acréscimo de 21% na eficiência em relação ao plástico de estufa e 150% em relação a configuração sem cobertura. A perda de carga ... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Drying is considered the greater energy expenditure stage in the grains production, being usually carried out with biomass burning, such as firewood. Financially, grains drying process continues to be costly and infeasible for small farmers. The objective of this study was to design, build and evaluate the technical and economic feasibility of a solar collector with a spiral polyethylene tube for grain drying process in a fixed plate for small farms. The collector was tested in three different conditions: without cover, with greenhouse plastic cover and with glass cover. The collector area is 4,18m2. The collector characterization was done measuring the thermal yield, its efficiency curve and collector load losses. The drying system performance was determined by the specific energy consumption, drying time, grain and plenum temperature and drying cost. A simulation of drying time and cost was also performed in comparison to commercial dryer. The collector with glass coverage obtained the best results with average temperature at the collector outlet of 69,87 °C, 35° C inlet and 19% of thermal efficiency. The coefficients of absorbance and losses were FR(τα) = 0.150; FR UL 1,101, respectively The glass provided 21% increase in efficiency compared to the plastic cover and 150% relative to the configuration without cover. The pressure drop for all configurations was around 40 mmca. The drying time was 4,5 hours, the specific energy consumption was 280,96 KJ/kg and the drying system efficiency was 11,6%. The cost of manufacture of the equipment was R$ 1.296,00 and in the drying simulation was found that to dry 20 bags of corn the cost was R$ 3,56 per bag, requiring 3 collectors and a total time of 24 hours / Doutor

The goal of the research paper was to understand the complex relationship between the issue of sustainability and maize farmers’ decision-making processes. The aim is to shed light on the realities experienced by maize farmers in terms of how sustainability impacts on the decisions they make and how the decisions they make impact on sustainability. The importance of the research lies in the current state of affairs in the world in terms of the current economic recession, overpopulation, dire poverty and hunger, and the poor state of the environment. If humankind is to continue its existence on Earth in a happy, healthy world, something is going to have to give. In order for this to happen, people need to start grappling with the concept of sustainability. Focusing on sustainability as a whole is likely to end in despair. However, breaking the problem down into its component pieces will allow people to influence the particular sector in which they operate. It is therefore imperative for research into sustainability to be undertaken in all sectors of society and the economy. Agriculture presents an excellent research area due to its intrinsic link with the environment, society and the economy. Agriculture and its wellbeing is inextricably tied to environmental health. Healthy plants and animals will not grow in unhealthy conditions. Society is to a large degree dependent on agriculture for food, agriculture therefore has a significant impact on social order and function. Agriculture is one of the primary contributors to GDP, particularly in poor and developing nations. As a result, agriculture has an important role to play in ensuring economic sustainability. In order to engage with sustainability from an agricultural perspective it was decided to engage on the farmer-level. Gaining an understanding of their reality in terms of what motivates their decisions is key to understanding the relationship between agriculture and sustainability. Three maize farmers in Mpumalanga, South Africa, were interviewed with the aim of collecting qualitative data and then analysing the data using thematic analysis. The methodology employed enabled the researcher to uncover patterns in the data that constituted themes across the interviews. The following themes emerged: Theme 1: Economic factors are the primary decision driver. This is primarily due to the extent of the financial risk experienced by farmers as a result of market risk, production risk, finance risk, and rising input costs. This results in economic considerations superseding environmental or social concerns in farmers’ decisions. This has a negative impact on the overall sustainability of the farming operation. Theme 2: There has been a decrease in the number of family-run farms. This is attributable to a number of factors including economic failure, fear of loss of land due to land-reform policies, as well as crime. Family-run farms tend to have a greater focus on sustainability due to the vested interest in the next generation taking over the farm. The corporate farming operations that are taking over the farms tend to be more focussed on short-term gains in order to satisfy shareholders. Theme 3: Mechanisation is preferable to manual labour. There has been an alarming decrease in the number of labourers employed on farms. Farmers say this is due to two factors. Firstly, machines are more efficient than labour. Secondly, restrictive labour laws have made famers less keen to employ people. The net effect of these two factors is that unemployment is rising. This has negative consequences for society, the economy, and the environment. Theme 4: Farmers believe they do very little environmental damage. This results in decisions being made that do not consider environmental wellbeing other than soil health. This is because farmers see healthy soil as an integral input that optimises economic performance. Farmers tend to prioritise economic factors in their decisions more than environmental or social factors. This results in an unsustainable perspective. The only ways in which this is likely to change is if the financial risk associated with agriculture is decreased, or if farmers are given financial incentive to change their ways. In order to deal with this issue it is necessary for further research to be conducted. Research needs to be conducted to confirm the results of this study. It is important to know whether the results pertain only to maize farmers in Mpumalanga or whether most farmers in South Africa, and indeed the world, face similar problems. Research should also be conducted to propose policies or procedures to reduce financial risk in agriculture. Research should focus on reducing market risk and reducing input costs, possibly via subsidisation.

Breeding maize (Zea mays L.) for tolerance to acidic soils could improve maize yields. The current study aims to identify maize genotypes with tolerance to acidic soils, as well as identifying secondary traits associated with the tolerance to soil acidity. Ten maize varieties were screened for tolerance to aluminium (Al) toxicity under glasshouse, laboratory and field conditions. In the glasshouse, two soil acidity levels (limed and unlimed soil) were used and the experiment was set up in a complete randomised design (CRD) with three replications. The experiment lasted for 10 days and measurements were taken on plant height (PH), leaf area, stem diameter and dry matter. In the laboratory, a haematoxylin staining (HS) experiment was conducted to determine the response of 10 maize varieties to Al toxicity. Two Al concentrations (0 and 222 μM) were used and the experiment was set up in a completely randomized design with three replications. After 7 days, shoot length, was recorded. Five stress tolerance indices were estimated to determine the resilience of each genotype. A root growth stress tolerance index was also computed for both experimental procedures. In the field, two trials were established at two sites, namely Mbinja and Mpumaze. Limed and unlimed plots were used, and the trial was set up in a randomized complete block design with three replications. Maize kernel yield and other standard field parameters were recorded. Selection of tolerant genotypes from the field screening was also done using three indices, namely harmonic mean (HM), stress tolerance index (STI) and stress susceptibility index (SSI). Both the glasshouse and laboratory assays identified similar genotypes of maize as being tolerant. These tolerant genotypes were Ngoyi, PANBG3492 BT, PAN 6Q408 and PHB 3442 based on the root growth stress tolerance index (RGSTI). It was therefore demonstrated that these two assays produced the same level of efficiency in identifying tolerant genotypes using this index. Based on ranking of seedling vigour index under soil acidity stress, the top three genotypes at Mpumaze were PHB32W71, PAN6616 and Sahara while at Mbinja, the top three were PAN6616, PAN6Q408 CB and PAN6P110. The genotypes PANBG3492 BT, PAN6Q408 and PHB3442 were also found to be tolerant to acidic soils at seedling stage. These genotypes are recommended for further evaluation in more sites to confirm their tolerance and yield potential under acidic soils. The study also revealed that plant height, leaf area and stem diameter could be used for indirect selection for tolerance to Al toxicity under glasshouse conditions. The seedling vigour index was also effective in identifying tolerant genotypes under glasshouse conditions. On the other hand, shoot length stress tolerance index and the haematoxylin score were useful for indirect selection for tolerance to Al toxicity in the laboratory. In the field, it was observed that ear length, leaf area and ear diameter can be useful in identifying genotypes that are tolerant to soil acidity. They can therefore be useful as indirect selection criteria under field conditions. Additionally, the best selection indices for identifying soil acidity tolerant genotypes under field conditions were the HM and the STI. It is recommended that varieties that were identified as tolerant be further evaluated in several soil acidity hot spots to confirm their tolerance and stability of performance under field conditions. / Agriculture and  Animal Health / M. Sc. (Agriculture)