Browsing by Author "Potgieter, Johan"

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    Controlled release fertiliser as a management tool for productivity of tunnel-grown tomatoes
    (Stellenbosch : Stellenbosch University, 2022-04) Potgieter, Johan; Le Roux, Marcellous; Stellenbosch University. Faculty of AgriSciences. Dept. of Agronomy.
    ENGLISH ABSTRACT: To be able to grow crops such as tomatoes on a commercial scale under stringent controlled conditions in what is termed controlled environment agriculture (CEA), requires a great amount of expertise and technology. Therefore, the aim of this study was to see if the use of controlled release fertilizer as an alternative low expertise and low technology-based fertilization method could produce the same yields and marketability than the conventional fertigation fertilization methods used in greenhouse tomato production. The study assessed this by (1) determining if the ratio of perlite to coco coir in the growth medium had any effect on the yield response to an industry recommended controlled release fertilization recommendation, (2) trying to establish an appropriate mixing ratio of controlled release fertilizer (CRF) and liquid fertilizer (LF) to determine if a follow up fertilization application of the pre-plant applied CRF can obtain improved yields. From the results it was evident that by applying a mixture of 80% CRF (based on the fraction of the total % nitrogen applied) and 20% LF with additional monthly manual application of calcium sulphate or calcium nitrate to each planting bag, CRF could potentially replace a 100% LF fertilization programme in greenhouse tomato production. Some results here indicate that a spike in temperature at the beginning of the growing season may have contributed to the premature release of nutrients from the CRF prill, causing a spike in EC. This stunted the growth of the plants for the rest of the season, which could have been attributed to an initial toxic level of salts in the rootzone and a prolonged deficit of other essential nutrients. The growth media trial for the determination of the optimal perlite: coco coir ratio revealed that a mix consisting of 20% perlite to 80% coco coir, or 40% perlite and 60% coco coir were the best ratios that yielded the highest. Thus, for tomato production the effect of CRF would be greatly improved if applied in an environment where the temperature and growth media properties are favourable for the slow release of the nutrients. The evidence here did not support the utilisation of 100% CRF as a replacement of the currently employed LF for commercial greenhouse tomato production. In addition, it is imperative that additional calcium (Ca2+), Sulphate (SO42-) and Nitrate (NO3-) be supplemented to reap the full benefits of CRF due to the ongoing technological research into the ability to coat calcium-based fertilizer products as a CRF.
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    Thermo-economic analysis of a french fries processing plant at Lambert's Bay
    (Stellenbosch : University of Stellenbosch, 2004-12) Potgieter, Johan; Harms, T. M.; University of Stellenbosch. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
    ENGLISH ABSTRACT: In the literature study energy efficiency is discussed in general, as well as certain critical areas of importance to this study. In addition, measuring and monitoring equipment, and energy inefficiencies in steam and refrigeration systems are reviewed briefly. In the energy analysis, an energy audit strategy is discussed in general. A walkthrough audit of the plant was conducted with specific focus on visible losses in the steam, refrigeration and production line systems. An energy analysis, as discussed in Chapter 3, indicates the main energy consumers, with steam being the biggest consumer of energy. The main consumers of refrigeration energy are the cold stores, flow freezer and blast freezer. Energy consumption in the cold stores can be minimised mechanically, while refrigeration energy of the flow freezer and blast freezer can be minimised through the modification of production activity. The main consumers of steam at the processing plant are the dryers, oil fryer, blanchers and steam peeler. Improved energy savings at the dryers can be obtained through optimisation of moisture and heat transfer mechanisms, while the energy of the blanchers and steam peeler can be combined by means of heat exchangers. The transfer of waste energy by means of a finned-tube heat exchanger from the steam peeler to the blanchers was investigated. The newly installed coal boiler shows capacity for improving the quality of steam, as well as efficiency, by incorporating an economiser and separator for improving steam quality, automatic TDS control and blow-down heat recovery. The product life cycle is discussed considering future automation that could lead to energy and labour savings. Lastly the utilisation of product waste as a future research subject is discussed. A confidentiality agreement was entered into with Oceana.