Masters Degrees (Agronomy)

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    The response of two Cape gooseberry varieties to organic amendments on degraded soils in the Western Cape, South Africa
    (Stellenbosch : Stellenbosch University, 2023-03) Tuaandi, Dolly; Tshuma, Flackson; Swanepoel, Pieter Andreas; Stellenbosch University. Faculty of AgriSciences. Dept. of Agronomy.
    ENGLISH ABSTRACT: The Cape gooseberry crop has the potential to enhance food security, especially for marginalised communities and small-scale farmers. The plant can be utilised from the roots to the fruit and has medicinal properties such as withanolides, antioxidants and phytochemicals which are used in pharmacology. Despite its potential benefits, there is limited published information on the production of the Cape gooseberry plant, especially under organic soil amendments, in South Africa. The aim of this study was, therefore, to investigate the effects of the organic amendments; vermicompost (VC), and effective microbes in combination with vermicompost (EMV), on selected soil chemical parameters, and the productivity of the Cape gooseberries. The organic amendments were incorporated into the soil before the seedlings were transplanted and grown in a plastic tunnel. The control treatment did not receive any soil amendment. For the VC treatment, vermicompost was applied in each plot at a rate of 3 kg m⁻², whereas for the EMV treatment, 50 g of effective microbes plus 3 kg m⁻² vermicompost was added to the soil. To determine the effect of organic amendments on the productivity of Cape gooseberries, some plant growth parameters (plant height, stem diameter, chlorophyll content, leaf area index, fruit yield, and single fruit weight) were recorded. For standard soil analysis, soil samples were randomly collected from each plot at a depth of 0 - 150 cm. Results show that the use of organic amendments led to plant growth and productivity parameters which compared well with production under chemical fertilisers. Also, the use of organic amendments led to a reduction in soil nutrients, when compared to the initial soil status, which could be one of the reasons why fruit yield was significantly greater under organic amendment than under the control treatment. The study findings show that organic amendments can be a sustainable alternative to chemical fertilisers in Cape gooseberry production. Vermicompost was found to be the best option and is recommended instead of a combination of effective microbes and vermicompost as the addition of effective microbes did not significantly improve the gooseberry fruit yield and quality. In addition, the study has the outcome of three post-harvest diseases in Cape gooseberries. The diseases were caused by Rhizopus stolonifer, Botrytis cinerea, and Penicillium spp.
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    The use of a starch-based superabsorbent polymer to support and optimise potato production in the sandy soils of the Sandveld production region in South Africa.
    (Stellenbosch : Stellenbosch University, 2023-03) Smit, Lome; Swanepoel, Pieter Andreas; Steyn, Martin; Denner, Freddie; Stellenbosch University. Faculty of AgriSciences. Dept. of Agronomy.
    ENGLISH ABSTRACT: Trends in agriculture are rapidly shifting towards more sustainable approaches. This is no different for the ecologically sensitive Sandveld region, where agricultural activities put pressure on the indigenous biodiversity and available resources. Potato production in the Sandveld region is highly reliant on groundwater resources for irrigation purposes, due to the low annual precipitation coupled with very high evaporative demands, especially in summer months. Additionally, potato crops are sensitive to water stress and the crop’s poorly developed rooting system is inefficient in extracting the already low plant available water in sandy soils. The aim of this study was to evaluate the potential of the biodegradable superabsorbent polymer, Zeba™, to support and improve potato production systems in semi-arid, drought prone areas. This study was approached by means of a field trial as well as a supplementary pot trial. In the field trial, four rates of Zeba™, were applied in- furrow at planting, and compared to a control. Soil water content measurements showed that the soil layers from the treatments contained more moisture than the control. Generally, increased potato tuber yield (P<0.05) was observed with increasing rates of Zeba™, except for the highest treatment rate, which had a similar yield as the control (P>0.05). The application of Zeba™ did not adversely affect the tuber quality. The increased tuber yields resulted in improved resource-use efficiencies. The water-use efficiencies, as well as nutrient-use efficiencies were either higher, or equivalent, to values reported for previous research in the area. Three application rates, similarly as three of the rates in the field trial but adjusted for a 15 cm pot, were compared to a control in a pot trial. The water holding capacity of the soil and polymer system was assessed one day, and three days after a weekly irrigation event. The trial was run over a twelve week period. The results showed that both the treatment rate and the time intervals had a significant influence on the water holding capacity of the soil. Similar to the findings of the field trial, the water holding capacity increased with an increase in product applied. The use of the superabsorbent polymer had a more pronounced effect on the water holding capacity as the soil dried out after the irrigation event, due to its superior ability to retain water compared to the large pores of sandy soils. In comparison to the control, the use of this product retained more water on the third day after irrigation than on the first day after irrigation. Although a decrease in water holding capacity was observed as the trial progressed, there was no clear indication that it was due to a reduction in the polymer's absorption ability from degradation. The decrease observed is ascribed to the increase in temperature, which led to a higher evaporation rate. Zeba™ successfully improved potato production in the Sandveld by increasing the water holding capacity of the sandy soils, leading to an increase in fresh tuber yield and improved resource use efficiencies. A treatment rate of 10 kg ha⁻¹ of Zeba™ is recommended as optimal to support and optimise potato production in the Sandveld region. This product could also be used to sustain production in other semi-arid regions and drought prone areas, with similar soil textures, when water stress limits production.
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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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    The influence of zinc content on wheat seed quality and vigour
    (Stellenbosch : Stellenbosch University, 2021-12) Shandu, Minenhle; Pieterse, P. J.; Stellenbosch University. Faculty of AgriSciences. Dept. of Agronomy.
    ENGLISH ABSTRACT: It is the objective of every farmer to obtain high yields and therefore the use of good quality seeds is of importance. Most soils that support wheat cultivation are zinc (Zn) deficient. Biofortification was shown to be a solution to improve mineral content (particularly Zn) of cereals. Improved Zn content has secondary benefits during seedling development under Zn deficient conditions. On the other hand, yields are limited by other factors such as weeds, soil borne diseases and environmental stresses such as extreme drought conditions. All these factors reduce productivity of wheat, which have implications for global food demand to meet a growing population. The use of seeds with high vigour ensure investment returns because these seeds are believed to have better germination and tolerance against biotic and abiotic stresses. This study aims to investigate the influence of seed Zn levels on vigour of wheat accessions with varying quality attributes. Seed Zn has been associated with improving agronomic traits such as germination and optimum field emergence. The influence of seed Zn was investigated through laboratory and field experiments. Vigour was determined using the EC test, standard germination test, according to ISTA and accelerating ageing test (AA). Field experiments were conducted at two different localities, namely Langgewens and Roodebloem, respectively. Proper mineral content is vital for germination and zinc has been reported to improve vigour of seeds. The electrical conductivity (EC) test provided the best estimate of seed vigour, R1H (51.3 mg kg-1) had the least electrolyte leakage as well as, the best germination (>80%). Results indicated that seed vigour is affected by age, seed Zn concentration and locality of the seeds and their weight. Adequate Zn in wheat is an essential micronutrient required during physiological processes like germination. Accessions were one year apart with optimal germination from one-year old accessions. Due to natural ageing or artificial ageing, seeds lose vigour over time. The potential of using Zn-biofortified seeds still need to be investigated further because some of the accessions which had low zinc content managed to perform similarly to high Zn content accessions. Increasing sowing depth had a significant effect (p>0.05) on germination and emergence of wheat. This study revealed that seed Zn is beneficial to a seedling during early development. In field experiments and despite variation in seed Zn concentrations, both experiments at Langgewens and Roodebloem had uniform canopies at harvest. The benefits of high seed Zn content were inconclusive. Zinc biofortified seeds had an advantage of better germination and good establishment under different environmental conditions. However, the benefits of high seed Zn concentrations seemed to be sensitive to the availability of Zn in the soil. Zinc plays a crucial role in early stages from germination to emergence and early growth stages (tillering) but does not seem to influence the growth of wheat at later growth stages.
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    Use of biostimulants to assess the production of the underutilised legume, Bambara groundnut
    (Stellenbosch : Stellenbosch University, 2021-03) Zidubule, Siphiwo; Phiri, Ethel E.; Mothapo, Palesa Natasha; Stellenbosch University. Faculty of AgriSciences. Dept. of Agronomy.
    ENGLISH ABSTRACT: Underutilised crops are an important part of local diets but have not been fully adopted in modern agriculture. Often, they are cultivated in marginal lands with low, if any, nutrients. The need for underutilised crop research becomes apparent not only because a big portion of plant based human food is mainly derived from a limited number of staple crops. With the threat of global warming and associated more extreme weather, and indirect impacts such as crop diseases, reliance on a few crops is a major challenge to food and nutritional security. Moreover, existing deficiencies of key vitamins and minerals pose a serious constraint to livelihoods, more especially in rural areas. Bambara groundnut (Vigna subterranea (L) Verdc.) is one of the crops that could be used to increase food production. With a reported high drought tolerance, Bambara groundnut is cultivated across Africa, but its full potential has not been realised and its agronomic performance scantily documented. Therefore, two greenhouse experiments, using two landraces of Bambara groundnut, were conducted at the Welgevallen experimental farm, Stellenbosch University, Stellenbosch. The aim was to investigate the effect of different biostimulants on the growth performance of Bambara groundnut. The specific objectives were to: (1) Evaluate the effect of different biostimulants on agronomic plant performance, (2) Assess the effects of biostimulants on the nutritional composition of Bambara groundnut seeds. The study consisted of five treatments (untreated control, chicken manure fertiliser, Kelpak®, humic substance and Moringa leaf extract, n=6 replicates each), conducted in a tunnel production system. Biostimulant treated plants reached 50% flowering significantly earlier that the control and fertiliser treated plant. Plants treated with Kelpak® showed significantly higher plant height, larger leaf area, and higher leaf dry matter relative to control and other treatments. Treatment with humic substance and Moringa leaf extracts resulted in higher yield parameters, number of pods per plant, 100-seed weight, and total seed yield were the highest in humic substance treated plants followed by Moringa leaf extract. Therefore, the humic substance showed the highest harvest index percentage relative to the other treatments. Of the three biostimulants treatments, Kelpak® treated plants produced the lowest seed yield. Using multiple linear regression we found that variation in total seed yield could be explained by the input of treatment, particularly humic substance and Moringa. Kelpak® was found to not have a significant effect on seed yield but rather on plant height and dry shoot mass, indicating better suitability to growing leafy vegetables than grain. The nutrient composition was improved under Moringa and humic substance treatment, meaning that these two factors not only improved plant growth and productivity but maintained the nutritional composition of Bambara. Therefore, biostimulant application positively influenced Bambara groundnut growth, development, and yield without compromising the nutritional content of the crop seeds. Therefore, biostimulants alongside appropriate levels of fertilization may be used to enhance the production of Bambara groundnut crops, and other underutilised and neglected crops. However, the results need to be validated by investigating the remaining landraces of Bambara groundnut. Keywords: Bambara groundnut, biostimulants, underutilised crops, landraces.