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 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.
- ItemGenetic, anatomical and morphological characterization of bambara groundnut (vigna subterranea (l.) Verdc) landraces in South Africa.(Stellenbosch : Stellenbosch University, 2023-03) Baloyi, Nsovo Happiness; Swanepoel, Pieter Andries; Voster, Alvera; Phiri, Ethel Emerentia; Stellenbosch University. Faculty of AgriSciences. Dept. of Agronomy.ENGLISH ABSTRACT: Bambara groundnut (Vigna subterranea (L.) Verdc), an underutilized grain legume that is typically grown by female subsistence farmers in the rural parts of Africa. However, it is grown at a low rate especially in South Africa with sowing rate ranging from 25-160kg per hectare. Although it has the potential to yield high amounts of seed and can grow under adverse weather conditions, among other benefits, it remains underutilized and under researched. To date there are no improved varieties and farmers therefore rely on indigenous knowledge systems to select varieties based on their preferences thereby unconsciously contributing to genetic erosion of the crop. The aim of this study was to characterize and determine whether bambara groundnut landraces classified based on seed coat colour are both morphologically and genetically similar, to eventually aid the selection of genotypes with favourable attributes for breeding programs and development of genetically enhanced varieties. An assessment of 48 landraces from the Limpopo province, South Africa, was undertaken using morphological descriptors like number of pods per plant and type of growth habit. Landraces were analysed for anatomical differences on the leaf epidermis such as trichome type and trichome density. The extent of the genetic diversity and population structure of the landraces were assessed through genotyping using Restriction-Site Associated DNA (RAD) Sequencing. Considerable differences in the yield parameters number of pods per plant, and growth habit were observed which means that some genotypes yield more than others. According to literature the type of growth that is preferred by farmers for efficiency during harvesting is the bunch and semi- bunch type because the pods attach to the crown of the stem while the spreading type is preferred for fields with weeds. Anatomical assessment of the leaf revealed that there are genotypes with high trichome density and two types of trichomes on the same plant which makes them more resilient to disease pressure than others. However, correlation and hierarchical cluster analysis indicate that these findings are not related to the seed coat colour which therefore means that use of one morphological character to classify genotypes into landraces should not be undertaken. This was further supported by the genotyping and population structure analysis results which indicated the presence of two sub-populations that are not related to seed coat colour. This the first report to highlight the importance of trichome type and density as a morphological descriptor to aid the selection of landraces for introduction into effective breeding programs.