Masters Degrees (Agronomy)
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Browsing Masters Degrees (Agronomy) by browse.metadata.advisor "Kempen, Estelle"
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- ItemCultivation aspects of hydroponic cut tulip (Tulipa gesneriana) production in South Africa(Stellenbosch : Stellenbosch University, 2013-12) Derbyshire, Geline; Kempen, Estelle; Hoffman, L. (Lynn) (Horticulturalist); Stellenbosch University. Faculty of AgriSciences. Dept. of Agronomy.ENGLISH ABSTRACT: Tulip cut flowers are considered speciality flowers, but are cultivated on a limited scale in South Africa. Published research done on the cultivation aspects of Tulipa spp. in warm climates is sparse and insufficient. The production potential of this valued floriculture crop under South African conditions however prompts a need for research as profitable returns can only be realised when cut tulip producers deliver high quality tulips, both for the local and potentially the export market. Understanding how cut tulips react to different cultivation aspects under local conditions is key in developing successful and profitable forcing programs for cut tulip production in South Africa. In order to produce quality tulips it is vital that producers minimize the occurrence of physiological disorders by optimizing cultivation aspects such as nutrition, bulb quality and age, cultivar selection as well as postharvest treatments. To study the nutritional requirements of cut tulips produced in a hydroponic system under South African conditions two similar experiments were conducted, using early-forcing and late-forcing tulip bulbs respectively. In each experiment the effect of four different nutrient solution formulations (“Current SA”, “Standard Steiner”, “Europe”, “Europe+NH4”) and four different cut tulips cultivars (‘Leen van der Mark’, ‘Jan van Nes’, ‘Ill de France’, ‘Royal Virgin’) on growth, quality and vase life was evaluated. Results showed that although nutrient solutions did not significantly affect the scape growth of cut tulips, vase life was significantly affected by nutrient solution formulation for both early- and late-forcing bulbs. For early-forcing bulbs nutrient solution “Europe” produced tulips with a significantly longer vase life than other nutrient solutions and for late-forcing bulbs nutrient solution “Standard Steiner” produced tulips with a significantly longer vase life than other nutrient solutions. Cultivars differed significantly in terms of growth, quality and vase life for both early- and late-forcing bulbs. It was found that the cultivar ‘Leen van der Mark’ presented the longest stem length, greatest fresh weight and longest vase life of all cultivars evaluated for both early- and late-forcing bulbs and it seems to be a cultivar with a low risk in terms of quality and vase life for forcing hydroponically in warm climates. As stem topple, a physiological disorder which can be prevalent in hydroponically produced tulips, has been shown to be reduced by the application of calcium fertilizers, the next experiment was conducted to investigate the role of foliar sprays to reduce or eliminate this common disorder. Various foliar spray treatments, including calcium nitrate (CaNO3), CalTrain, NonTox Silica® and an untreated control, were evaluated for their effect on the occurrence of postharvest stem topple and the vase life of the two tulip cultivars ‘Jumbo Pink’ and ‘Strong Gold’ respectively. Trends indicated that foliar sprays containing calcium, “CaNO3” and “CalTrain”, reduced the incidence of postharvest stem topple. The vase life of hydroponically forced cut tulips was significantly increased by the use of foliar fertilizer sprays as compared to the control. The vase life of cut tulips is an important parameter directly affecting quality. In a final experiment, the efficacy of three postharvest treatments to extend the vase life and minimize postharvest stem elongation of the four cut tulip cultivars ‘Deshima’, ‘Synaeda Orange’, ‘White Marvel’ and ‘Margarita’ was evaluated. Treatments consisted of an untreated control, an overnight stem pulse of Chrysal BVBPlus, a four hour fumigation of Chrysal Ethylene Buster® (1-MCP) and a combination of the latter treatments. Vase life, postharvest stem elongation and vase-solution used were parameters measured. No statistically significant effects on any parameters measured could be identified between the various treatments. Trends observed suggest that treatments containing BVBPlus may prolong the vase life, minimize postharvest stem elongation and improve the usage of vase life solution of hydroponically produced cut tulips. BVBPlus thus shows potential for use as an essential postharvest treatment for cut tulips produced hydroponically under warm climate conditions, but further research is needed for conformation. This research is a first report on key agronomical aspects of the hydroponic cultivation of cut tulips in South Africa and aims to serve as a basis for future research, ultimately to support successful commercial cultivation of tulips on a larger scale in South Africa as well as internationally.
- 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.
- ItemEffects of pruning and nutrition on growth and yield of hydroponic tomatoes (Lycopersicon esculentum Mill)(Stellenbosch : Stellenbosch University, 2011-12) Fulton, Craig Mark; Kempen, Estelle; Stellenbosch University. Faculty of AgriSciences. Dept. of Agronomy.ENGLISH ABSTRACT: The potential importance of soilless production, particularly in tomatoes, in an increasingly water scarce South Africa prompts a need for research under local conditions. In soilless production systems the application and availability of nutrients is closely linked to that of water, necessitating the research of methods to increase water and fertiliser use efficiency in soilless production systems, while diminishing environmental pollution and maintaining, or ultimately improving, tomato yield and quality. Poor management of hydroponic fertigation water results in pollution, and wastes precious water and expensive fertiliser. Pruning is an important cultural practise for ensuring high productivity of hydroponic tomatoes. Adapting pruning practises to climatic conditions could be a cheap and effective manner to improve productivity without increasing inputs. Improving water and fertiliser use efficiency is crucial to ensuring sustainable production of intensive crops, such as the tomato. Three experiments were carried out to investigate the effects of pruning and fertilisation on growth and yield and water and fertiliser use efficiency of hydroponic tomatoes. In the first experiment the effect of EC (electrical conductivity), irrigation frequency and growing media on water use, nutrient uptake, yield and quality of greenhouse tomato was examined. A factorial design with split plots was used. Two EC treatments (1 and 2 mS.cm-1) in factorial arrangement with 3 irrigation treatments (5x, 10x, 20x) were applied to the main plots. Plants grown in different growing media (coir, sand, sawdust) represented the split plots. Plants grown at EC 1 mS.cm-1 were still able to uptake sufficient nutrients to achieve leaf nutrient contents associated with optimal production. Also, increasing the absolute nutrient concentration had a small effect on nutrient uptake. The organic media, coir and sawdust, reduced available N early in the tomato crop life, and tomatoes grown in coir had reduced Ca uptake compared to plants grown in sand and sawdust. Coir grown plants used more water compared to sand and sawdust grown plants. Plants grown at EC 1 mS.cm-1 used less water compared to plants grown at EC 2 mS.cm-1. Tomatoes grown at an EC 1 mS.cm-1 did not differ significantly from higher EC plants in terms of marketable and green fruit yield. Plants cultivated at the lower EC had significantly lower percentage soluble solids content (Brix) compared to the higher EC treatment. The second experiment examined the effect of leaf and fruit pruning on fruit size, total yield and marketable yield of tomatoes. Plants were grown using the high wire system and pruned to two stems. Three different leaf pruning treatments were applied: no leaf pruning, pruning every 2nd young leaf after 1m plant height, and pruning every 2nd young leaf after 2m plant height. Two fruit pruning treatments were also applied: no fruit pruning and trusses pruned to 4 fruits. The experiment used a factorial design. Leaf pruning treatments had no effect and this was probably due to too late a removal of young leaves. Fruit pruning resulted in no significant difference between treatments in terms of marketable yield. Plants with unpruned trusses did have a significantly higher total yield, higher early yield, lower average marketable fruit weight, and higher yield of unmarketable fruit (particularly small fruit compared to the pruned treatment). From these results it can be concluded that fruit pruning isn’t necessary on short tomato crops but this may be different over a longer cropping cycle. The third experiment determined the combined effects of different EC and stem pruning practices on nutrition, growth and early yield of hydroponically grown tomatoes in coir. A factorial design was used, with two EC treatments (1 and 2 mS.cm-1) in factorial arrangement with 2 stem pruning treatments (single and double). Stem pruning had little effect on plant growth but did alter plant development. Plants pruned to two stems produced significantly more trusses, but did not produce a significantly higher DM or leaf area compared to single stem plants. Stem pruning’s major effect appears to be influencing fruit load; this may in the long term result in differences in plant growth and nutrition. EC 1 mS.cm-1 plants produced significantly lower leaf area and organ dry masses but had a significantly higher marketable yield compared to EC 2 mS.cm-1 plants. Over fertilisation in young tomatoes can negatively impact on early yield, whereas lower fertiliser application in early tomato growth improves early yield but limits canopy development which may limit plant productivity in the long term. These differences in growth are believed to be primarily related to differences in N and P nutrition.
- ItemImproved potato (Solanum tuberosum) seed production through aeroponics system(Stellenbosch : Stellenbosch University, 2014-04) Tshisola, Steve Ndondji; Kempen, Estelle; Van Zyl, Jacques; Stellenbosch University. Faculty of AgriSciences. Dept. of Agronomy.ENGLISH ABSTRACT: The potato can be considered as one of the most important food crops in many African countries. The potential of this crop is reflected in the large increase in area of production where Africa showed the highest rate of growth within the developing world over the past twenty years. The multiplication rate of potatoes is very low compared to other crops. Therefore it is essential to investigate methods of increasing the number of minitubers produced from disease free in-vitro plantlets. There is a number of potato propagation procedures that are currently being used worldwide to multiply seed potatoes. As aeroponics is still a relatively new technique that has not been researched extensively for the production of minitubers, a study relating to the production practises including the nutritional requirements of potato minitubers produced in a aeroponic system were undertaken. Potato plantlets, cv BP1, were grown aeroponically at two different densities (20 and 30 plants/m2) and four harvest intervals (7, 10, 14 and 18 days). The interaction between harvesting intervals and plant densities did not influence plant growth, minituber quality or yield. Best results were realised when harvesting every 7 days with a higher total tuber number over the growing period. Harvest interval also influenced the phosphorus and copper concentration in minitubers. To study the effect of Calcium (Ca) application rate, potato plantlets of cultivars Up-to-date, Mnandi, Buffelspoort and BP1 were grown at four different Ca levels (8.40, 6.75, 5.10 and 3.45 meq/L). The interaction between Ca application levels and cultivars significantly influenced the percentage stolon branching. BP1 had more stolons at the lowest Ca application level and Buffelspoort had more stolons at the full Ca application levels. However, low Ca treatments produced the highest yield. The minituber number and weight harvested were three times more for Mnandi. An aeroponic study on the irrigation frequency (20, 30, 40 and 50 minutes interval) was conducted on four potato cultivars (Up-to-date, Mnandi, Buffelsoort and BP1). Significant differences were noted in the interaction between irrigation frequencies and cultivars for the percentage tuberised plants and stolon and tuber dry mass. When irrigated every 40 minutes, 48% of the Buffelspoort plants produced tubers. Plant height was also significantly affected by the interaction between irrigation frequencies and potato cultivars, with Mnandi producing taller plants when irrigated every 30 minutes. Total tuber number and tuber fresh and dry weight was higher at the irrigation frequency of 20 minutes. The interaction between irrigation frequencies and cultivars on the response to macro and trace elements was not significant for sodium and iron but was for phosphorus, potassium, calcium, zinc and aluminium. A field study was conducted in a greenhouse where potato seed of BP1 obtained from the first trial were graded into different sizes (Small: >20, medium: 20–40 and large: > 40 mm of diameter) and stored at 3 different temperatures (3, 16 and 25oC) for 2 supplementary months before being planted. Sprouting capacity was mostly influenced by temperature regardless of other factors applied to potato seed minitubers such as harvest intervals and sizes. The higher storage temperature of 25oC resulted in tubers with a higher number of sprouts, longer sprouts and with a higher sprouting capacity.
- ItemInfluence of calcium on yield and quality aspects of potatoes (Solanum tuberosum L.)(Stellenbosch : Stellenbosch University, 2017-03) Gumede, Thabani; Kempen, Estelle; Stellenbosch University. Faculty of AgriSciences. Dept. of Agronomy.ENGLISH ABSTRACT: The potato (Solanum tuberosum L.) is an adaptable crop, and modern varieties make its cultivation feasible in numerous parts of the world. The high production potential of the potato ensures that it has the potential to contribute significantly to the world’s food requirements. Correct fertilisation is an important factor in potato production to obtain maximum yields and high quality tubers. Calcium (Ca) is an essential plant element and plays a significant role in the potato plant by maintaining cell membrane and cell wall structure. Recent studies have indicated that tissue Ca level is linked to the quality of various fruit and vegetable products. In the case of potatoes a reduction in tuber internal defects and an improvement in storability can be expected with an increase in tuber Ca. The mechanism of Ca uptake by the potato plant and translocation of Ca within the plant however inhibits the uptake of Ca into the tuber. Thus the present study aims to evaluate the methods to improve Ca tuber content and tuber quality aspects. Potato seedlings of four cultivars (Mondial, Sifra, Lanoma and Innovator) were used in a tunnel where different concentrations of Ca (1.1, 3.2, 6.6 and 9.8 meq Ca L-1) were applied. Tuber mass, shoot fresh mass and shoot dry mass was affected by the Ca application levels and also differed between the cultivars. Mondial, a popular South African cultivar, performed best in terms of tuber yield. Application of 3.2 meq L-1 Ca through drip irrigation was most beneficial to yield parameters (tuber yield, shoot fresh mass and harvest index). To study the Influence of different calcium application levels on potato plants under low temperature growing conditions, potato seedlings of cultivars Destiny and Lanorma, were transplanted into 3 m3 bins containing three different soils (sandy, sandy loam and loam) during the winter season. Three calcium application rates (1.1, 3.2 and 6.6 meq Ca L-1) were applied through drip irrigation. The interaction between Ca application levels and cultivars significantly influenced tuber mass, shoot fresh and dry mass. The influence of Ca as a foliar application on the growth, yield and quality aspects of potatoes was also investigated. Two cultivars (Lady Rosetta and Mondial) were used in a trial where different concentrations of Ca were applied as foliar application or soil drench, during tuber bulking and maturation. None of the parameters measured; tuber fresh mass, tuber number, specific gravity, percentage dry mass or chemical composition was significantly influenced by either the foliar application or soil drench calcium applications. It appears that supplemental Ca applied at these rates and time of plant development has no added benefit on yield or quality aspects of potato tubers. Calcium fertilisation can positively affect both yield and tuber quality but the rate and method of application are of utmost importance. Cultivars also respond differently to Ca application and producers should bear this in mind.
- ItemThe use of Flucarbazone-sodium to control wild oats (Avena spp.) in cultivated wheat fields of the Western Cape of South Africa(Stellenbosch : Stellenbosch University, 2017-03) Bester, Dirk Wouter; Kempen, Estelle; Stellenbosch University. Faculty of AgriSciences. Dept. of Agronomy.ENGLISH ABSTRACT: Wild oats (Avena spp.) is a prominent weed in cultivated wheat fields of the Western Cape Province of South Africa. For the sustainable production of wheat, it is crucial to apply the correct herbicide rates at the correct growth stages of both wild oats and wheat in order to achieve maximum weed control. Flucarbazone-sodium has shown to provide excellent activity against wild oats when applied as a post-emergence herbicide to wheat in field experiments conducted in Canada and the USA. Flucarbazone-sodium acts as an inhibitor of the enzyme acetolactate synthase (ALS) also known as acetohydroxyacid synthase (AHAS), an important enzyme that acts as a catalyst in the biosynthesis of the branched-chain amino acids leucine, isoleucine and valine. This product, known as Everest® 2.0, is a new sulfonylaminocarbonyltriazoline herbicide on the South African market. Flucarbazone-sodium has not yet been tested scientifically under South African conditions. The environment, soil, wheat cultivars and cultivation techniques between South Africa and North America differ immensely. In this study flucarbazone-sodium was evaluated under South African conditions in the Western Cape. The first part of the study aimed to evaluate the phytotoxic effect of flucarbazone-sodium on the locally grown wheat cultivars of the Western Cape, as herbicides have no use if they reduce yield potential, regardless of how effectively they control weeds. For this study the internationally accepted BBCH scale was used to describe the different growth stages of the crop. Flucarbazone-sodium was applied at half, one and double the recommended rates at three different plant growth stages ([12-13], [14-15] and [16-17]; BBCH scale on five cultivars (SST 88, SST 027, SST 056, SST 015 and Pannar 3408) in a phytotoxicity field trial. Yield and grain quality (protein content, hectolitre mass and thousand kernel mass) was examined at the end of the growing season. Wheat yield was not negativly affected by flucarbazone-sodium applications, however, double the recommended rate showed a significant (p < 0.05) reduction in yield and hectolitre mass for cultivar SST 056. Appart from SST 056 there is no statistical evidence to discard flucarbazone-sodium in a weed management system, as long as the application guidelines on the product label are followed. To date, no studies have been published on the effectiveness of flucarbazone-sodium in controlling wild oats biotypes in South Africa. For this study, three sites in the Swartland area (Moorreesburg and Piketberg) with severe wild oats infestations were chosen. Flucarbazone-sodium was applied at half, recommended and double the recommended rates at three different growth stages ([12-13], [14-15] and [16-17]; BBCH scale of the wheat. The results showed that flucarbazone-sodium was very effective in controlling wild oats in cultivated fields at all sites except one. At the Pools site near Piketberg in the Western Cape very low levels of wild oats control by flucarbazone-sodium was recorded. Resistance was suspected and seeds were harvested for further investigation. Glasshouse and molecular trials were conducted in order to prove that the biotype present at Pools is resistant to flucarbazone-sodium and to investigate the possible mechanism responsible for this resistance. Results showed that the sampled wild oats biotype at Pools is clearly resistant to flucarbazone-sodium. Even at eight times the recommended rate, flucarbazone-sodium could not control a single wild oats plant. Flucarbazone-sodium appeared to have some effect on the wild oats biotype sampled at Pools, since the dry mass (DM) of the wild oats was negatively v affected as the dosage rate was increased. PCR results showed the sampled wild oats biotype had homozygous resistance mutations Ala-205-Val and Trp-574, and heterozygous resistance mutations Pro-197 and Ser-653. This is the first documented case of Ala-205-Val, Trp-574 and Pro-197 mutations present in Avena spp. worldwide.