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.
- ItemThe 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.
- ItemEffect of magnesium and boron on potato tuber quality(Stellenbosch : Stellenbosch University, 2022-04) Hindley, Renoir; Le Roux, Marcellous; Combrinck, Nicolaas; Stellenbosch University. Faculty of AgriSciences. Dept. of Agronomy.ENGLISH ABSTRACT: Magnesium (Mg) is an important macronutrient with the main function of facilitating various biochemical reactions and physiological responses throughout the development of plants. Magnesium serves as the central atom of chlorophyll molecules in green tissues, contributing extensively to plant assimilation. However, Mg-related studies in potato nutrition, particularly in terms of keeping quality, are poorly documented. Boron (B) is another nutrient that is often overlooked. This nutrient acts as a stabilizer of the cell wall pectin network and as a result enhances cell wall structure. Boron also facilitates the movement of sugar in the plant by forming sugar borate complexes or by linking with the cell membrane in order to enhance sugar permeability. The conversion of starch-to-sugar in tubers is known to affect the nutritional value of potatoes. In this study, greenhouse experiments were conducted to evaluate the influence of different levels of Mg and B against various parameters of potato tuber quality. Magnesium was shown to have a positive response on tuber weight and a shortage of it was detrimental to the storability of tubers. The most significant finding for B was its moderate improvement of starch content in tubers. In the first experiment, two cultivars were evaluated. Tuber number for each treatment combination was determined on day of harvesting. Tuber weight and specific gravity (SG) were performed using a weighing scale and the water displacement method, respectively. The harvests were stored in a dark room, at room temperature, for a six-week period in order to monitor the rate of weight loss. This was obtained by routinely weighing tubers on days 0, 7, 14, 21, 28, and 42 after harvesting. Thereafter, tubers were sent for starch determination that was done by means of the AMG / α-amylase / HK method. In the second experiment, the study to determine the effect of Mg and B in tuber quality was extended. In addition to number, weight, storage losses, and starch content, tubers were divided into weight classes of 50-100 g and 100-150 g, in order to analyse elemental distribution and periderm thickness, respectively. The distribution of elements was accomplished using a Scanning Electron Microscope (SEM). Potato samples that were used for the analysis of periderm thickness, was done by the help of MicroCT scans. The visualization of these samples was performed in Volume Graphics VGStudioMax 3.1. Taking into account the work of Rian Gericke (2018) in predicting the keeping quality of potato by way of tuber characteristics, where Mg correlated negatively with weight loss, the hypothesis in this study that Mg content would have a positive effect on the storage quality of tubers was true. Boron was shown to moderately improve starch content. The distribution analysis showing that Mg tended to locate near the stem-end, at a decreasing gradient towards the bud-end of tubers, was consistent with several previous studies. Unfortunately, the low levels of B were not detected in any of the samples by this method. In comparison to foliar applications, the supply of Mg through the soil was shown to have a more significant influence on periderm thickness, whereas the effect of B was unclear.