Masters Degrees (Agronomy)

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    Investigating herbicide resistant ryegrass
    (Stellenbosch : Stellenbosch University, 2024-03) Bestbeir, Louise; Viljoen, Charne; Pieterse, P. J. ; Stellenbosch University. Faculty of AgriSciences. Dept. of Agronomy.
    ENGLISH ABSTRACT: Multiple herbicide resistance is an escalating problem in weeds globally. Ryegrass (Lolium spp.) is a major weed in grain cropping systems with documented cases of multiple herbicide resistance across the globe to various amalgamations of glufosinate‑ammonium, glyphosate, acetyl CoA carboxylase, and paraquat. In South Africa, ryegrass plants that survived herbicide applications were tested for multiple herbicide resistance while concurrently investigating spray deposition and adaptations to ryegrass biology based on cropping systems, i.e., Conservation Agriculture ryegrass from Langgewens Research Farm (LS), and resistance. Herbicide applications on young ryegrass plants show a lower spray deposition in terms of Fluorescent Particle Coverage (%) on the adaxis (0.31% ‑ 1.28%) than abaxis (3.93% ‑ 18.13%). Dose-response models varied due to unexpected dose range extremes and showed no paraquat resistance in the LS ryegrass with a lethal dose (LD50) of 0.482X, where X is the recommended dose. Extreme resistance was seen in ryegrass plants from Welgevallen Experimental Farm with differences between the ryegrass plants from the trial field (WS = 11.787X) and the ryegrass plants along the trial field perimeter (WP = 21.727X). Spearman correlations between ryegrass biology and resistance found a strong negative association (r = ‑0.80) between seed weight, mean germination percentage and resistance. Lastly, Welgevallen plants were confirmed to be the first case of glufosinate‑ammonium, glyphosate and paraquat multiple herbicide resistance in a single ryegrass population.
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    The effect of foliar micronutrient applications on nutrient use efficiency in tomatoes
    (Stellenbosch : Stellenbosch University, 2024-03) Wolf, Anchen; Kempen, Estelle; Stellenbosch University. Faculty of AgriSciences. Dept. of Agronomy.
    ENGLISH ABSTRACT: Plant nutrient management through the application of a balanced nutrient solution is critical for the success of crops in intensive production systems. Over-application or unbalanced applications however can result in wasted resources and environmental pollution. This study explores the impact of micronutrient foliar applications of silicon (Si) and boron (B) on the post-harvest yield and quality of two tomato varieties in a fertigation system where the calcium (Ca²⁺) and potassium (K⁺) application ratio is adjusted. Using these fertigation systems, the objective is to determine whether the nutrient use efficiency (NUE) can be improved for tomato production systems with the respective treatments. The study was conducted in a greenhouse on the Welgevallen Experimental Farm in Stellenbosch, Western Cape. Two varieties of tomatoes were used, Floradade and Solarino RZ F1 (72-150). Seedlings were planted into 20 L bags with coconut peat as the growing medium. The trial comprised of four treatments with an open-hydroponic system where a foliar feed of Si, B, or a combination of the two was applied in conjunction with a fertigation solution where the Ca²⁺ % was adjusted or followed standard recommendations. This adjusted solution maintained an EC of⁻¹ where the Ca:K and Ca:Mg ratios were changed with reduced Ca²⁺ and increased K⁺ and Mg²⁺, whereas the standard solution had ratios according to the Steiner solution concentrations. Analysis of the data collected during the trial, both developmental and post-harvest, was done using R (R Core Team, 2023) and STATISTICA Version 13.3 (TIBCO Soft Inc. 2016) for statistical software. A full nutrient analysis was also conducted on the fruits. Standard fertigation treatments, specifically treatment 2 with the added Si foliar feed had the most significant effect on the vegetative growth parameters. The reduced fertigation treatments had a less significant impact on these parameters, although the rate of Ca²⁺ supplied to tomatoes can be reduced if managed correctly, and if amendments of B and Si are given. The adjusted Ca²⁺ % reported an 18% increase in NUE for the marketable weight of the harvested product, and an 8% increase for the marketable weight of all the treatments combined, allowing growers to receive a larger percentage of marketable product at the same input cost and volume of nutrients compared to the standard fertigation treatments. It is confirmed that the NUE can be improved in hydroponic tomato production where Si and B are applied as foliar feed substitutes for Ca²⁺ without compromising the quality and post-harvest shelf- life of tomatoes. The reduction of Ca²⁺ % in the fertigation and the addition of Si and B did not compete with standard fertigation treatments. This reduction of the input, however, allowed for an increase in the NUE of these treatments, allowing growers to receive a larger percentage of marketable product for the input cost and volume of nutrients compared to standard fertigation treatments.
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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.