Masters Degrees (Agronomy)
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- ItemInvestigating 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.
- ItemThe 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 2mS.cm⁻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.
- ItemThe impact of weevil predation on seed viability and agronomic performance of cowpeas, Vigna unguiculata L. (Walp)(Stellenbosch : Stellenbosch University, 2023-03) Dlamini, Welile Mlando; Wilson, Ida; Pieterse, P. J. ; Swanepoel, Pieter Andreas ; Stellenbosch University. Faculty of AgriSciences. Dept. of Agronomy.ENGLISH ABSTRACT: Cowpea, Vigna unguiculata, is a nutritious and high value legume that is often susceptible to weevil damage in storage. It is largely grown in Sub-Saharan Africa and a primary source of income for resource-poor farmers. Callosobruchus maculatus is an invasive pest of cowpea seeds in storage, better known as the cowpea weevil. In the larval stage, cowpea weevils consume food reserves from the seed endosperm. Unsuitable storage structures, where no methods of weevil control are applied, may increase weevil infestation of cowpea seeds in storage which hampers successful cowpea production. While attention is dedicated to understanding the role of generic cowpea seed damage to the legume’s production, there is a dearth of evidence on the impacts of the damage to different sites of the seeds. This study therefore aimed to quantify the germination rate of cowpea seeds damaged on different sites and assess the effect of the damage on cowpea seedling growth and yield. Undamaged cowpea seeds, also known as “black-eye beans”, were infested with cowpea weevils, then kept in storage for three months. The stored seeds were damaged on the top, bottom, side, back or hilum. Seeds with a single hole were selected from the infested seed and sorted according to the site of damage on the seeds. The positions of holes on seeds were used as treatments for the experiments and undamaged seeds served as the control group. Major findings were seed germination at day two showed a significantly poorer germination of top damaged seeds, relative to both undamaged seeds and the alternative damage sites. This result remained consistent for germination at day seven as well as for seedling height at two weeks. Seeds with a single site of damage at the top of the seed performed significantly worse than seeds where the damage was on other sites. At physiological maturity, plants grown from undamaged seed had the highest 100-seed weight. The seed weight obtained from seeds damaged at the top was significantly less than those obtained from plants grown from undamaged seed. These results suggest that farmers, to ensure seedling emergence, should refrain from planting cowpea damaged at the top, but they can still grow seeds with alternate holes. The results of the study will help farmers manage seed losses after storage, as some damaged seed can still be sown and will produce a yield. This is the first study of its kind, and it gives insight into the site of damage on seed and cowpea production. The findings could encourage further investigation into other legume crops that also suffer from weevil damage. In addition, conclusions from the study may be of practical value for smallholder farmers to support nutrition and food security in Africa.
- ItemThe 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.
- ItemStrategies to facilitate lime movement in no-tillage crop production systems(Stellenbosch : Stellenbosch University, 2023-03) Pellissier, Jean-Pierre; Swanepoel, Pieter; Labuschagne, Johan; Hardie-Pieters, Ailsa G.; Stellenbosch University. Faculty of AgriSciences. Dept. of Agronomy.ENGLISH ABSTRACT: Soil acidity, particularly in the subsurface, threatens the sustainability of no-tillage crop production systems. Two field experiments were conducted to generate a novel perspective on alleviation of soil acidity in no-tillage crop production systems. Experiment 1 was conducted over two years on a sandy loam Oakleaf no-tillage system in the Swartland region of South Africa, receiving an average rainfall of 509 mm yr⁻¹. Initial soil pH(KCl) values were 6.0, 5.3, 4.3 and 4.2 in the 0 – 5, 5 – 10, 10 – 20 and 20 – 30 cm depth increments, respectively. Treatments existed of lime incorporation, surface applied lime forms (i.e., class-A, pelletised and hydrated lime) and combined surface application of lime plus gypsum. Wheat (Triticum aestivum L.) and canola (Brassica napus L.) crop parameters were monitored in year one and two, respectively. Combined surface application of 0.55 Mg ha⁻¹ calcitic lime plus 1.25 Mg ha⁻¹ gypsum decreased (p < 0.05) exchangeable acidity in the 20 – 30 cm depth by 0.30 cmolc kg⁻¹ relative to the control at 12 months. Incorporation of 1.67 Mg ha⁻¹ calcitic lime through once-off strategic tillage with a chisel plough and the combined surface application of 0.55 Mg ha⁻¹ calcitic lime plus 1.25 Mg ha⁻¹ gypsum both raised (p < 0.05) soil pH(KCl) by 0.45 units in the 20 – 30 cm depth relative to the control at 18 months. Surface application of both 1.56 Mg ha⁻¹ hydrated lime and 1.75 Mg ha⁻¹ pelletised lime resulted in an over-liming effect of the 0 – 5 cm depth after 6 months. At 18 months, there were no differences (p > 0.05) in soil pH(KCl) in any depth increment (0 – 30 cm) between hydrated, pelletised or calcitic lime. Lime incorporation through strategic tillage with a chisel plough resulted in the lowest (p < 0.05) wheat plant population in year one. Leaf area index, above-ground biomass, yield and seed quality parameters were not affected (p > 0.05) by the treatments in both years. Experiment 2 was conducted over three years on a clayey loam (Witfontein) no-tillage system in the western Rûens region of South Africa, receiving an average rainfall of 529 mm yr⁻¹. Initial soil pH(KCl) was 5.4, 5.2 and 5.0 in the 0 – 5, 5 – 15 and 15 – 30 cm depths, respectively. Treatments existed of lime incorporation through once-off strategic tillage, surface application of calcitic lime and pelletised lime (surface applied and in-row placement). Barley (Hordeum vulgare L.) crop parameters were monitored in year one and three. At 30 months, incorporation of 2 Mg ha⁻¹ calcitic lime through once-off strategic tillage with a disc, chisel or ripper plough did not increase (p > 0.05) soil pH(KCl) relative to exclusive surface application of 2 Mg ha⁻¹ calcitic lime in none of the depth increments (0 – 5, 5 – 15 or 15 – 30 cm). Pelletised lime treatments, whether surface applied or placed in-row, did not show any superiority to surface applied calcitic lime in alleviating soil acidity. There was no treatment effect (p > 0.05) on barley crop parameters in year one or three.