<p>  </p> <p>Environmental conditions, like light quality and herbivory, can induce changes in plant physiology. Light quality can be manipulated using LEDs (light emitting diodes) to improve crop quality and yield in horticultural production. The manipulation of light quality has also been utilized in the management of agricultural insect pests. Previous research has provided evidence that changes in light quality can have effects on the growth and chemistry of cannabis crops (<em>Cannabis spp.</em>). Varieties of cannabis are grown for the production of the valued cannabinoids CBD and THC. Pest of cannabis include herbivorous arthropods that reduce hemp yield and quality. Arthropod herbivory can induce chemical and physical changes in plants. This thesis further investigates the role of light quality on both cannabis biology and the crop-pest interaction between cannabis and the cannabis aphid (<em>Phorodon cannabis</em>). In the experiments described herein, the effects of light quality and <em>P. cannabis </em>herbivory on cannabis were assessed by measuring impact on biomass accumulation, yield, and the production of CBD and THC. The effects of light quality on the life history traits of <em>P. cannabis </em>were also measured. Cannabis grown under red-blue light quality saw a reduction in vegetative growth but no reduction in yield. Light treatments had no measured effect on the concentrations of CBD and THC in the cannabis buds. Aphid herbivory decreased bud yield but increased vegetative growth. Aphid herbivory reduced the concentration of both CBD and THC in cannabis bud tissue. Under blue-rich light quality, <em>P. cannabis </em>experienced higher reproductive rates when compared to red-blue and full-spectrum lighting. </p>

Doctor of Philosophy / Department of Horticulture, Forestry, and Recreation Resources / Richard H. Mattson / Subjects of this research were 64 adolescents receiving treatment at two behavioral health service institutions located in an urban mid-western city. Both institutions provided horticultural therapy and non-horticultural therapy programs. Research subjects were adolescents with diverse treatment needs and their responses on research questions were inconsistent compared to other related studies with general population. Current research assessed the adolescents with horticultural therapy treatment and without horticultural therapy treatment in three aspects. First, the levels of psychological aspects of adolescents were assessed with the Rosenberg Self-Esteem Scale and Nowicki-Strickland Locus of Control Scale for Children. The levels of self-esteem and locus of control of adolescents with horticultural therapy treatment were not significantly different from those of adolescents without horticultural therapy treatment at both institutions. Based on the different level of worthiness and competence factors, it is recommended to design horticultural therapy programs focused on improving the worthiness factor of self-esteem. Second, the pastoralism disposition of the Children's Environmental Response Inventory was used to assess the level of environmental attitude of the adolescents with and without horticultural therapy treatment. Horticultural experience and environmental attitude had a positive relationship with most subjects. At one institution, the level of environmental attitude of the adolescents with horticultural therapy treatment was significantly higher than the adolescents without horticultural therapy treatment. The adolescents at the horticultural therapy program which was scheduled more frequently showed higher environmental attitude scores. To improve environmental attitude of adolescents, horticultural therapy program should provide diversity and abundant opportunities of horticultural experiences. Third, basic horticultural knowledge was tested with the Basic Horticultural Knowledge Questionnaire. Vegetable/fruit consumption and preference were described with the Vegetable and Fruit Preference and Consumption Survey. Basic horticultural knowledge scores of the horticultural therapy group were significantly higher than that of the non-horticultural therapy group at one institution, but the scores were similar between the two groups at the other institution. Basic horticultural knowledge of subjects was significantly correlated to their vegetable and fruit consumption. To increase vegetable/fruit consumption, horticultural therapy programs should set goals to incorporate nutrition education.

Thesis (MScAgric)--University of Stellenbosch, 2007. / ENGLISH ABSTRACT: The declaration of Namibia’s independence from South Africa in 1990 has seen the Namibian government aim to plan and implement development programmes that enhance a growing agricultural sector. The new government is facing challenges regarding the addressing of inequalities of income and the allocation and distribution of resources, which have resulted in implementation of the land reform programmes. On the international front, Namibia is a member country of various trade arrangements, such as the WTO, the SADC and SACU. The main driving force behind Namibia’s joining the international communities chiefly has been market access and trade policy reforms. The country’s agricultural sector, in particular the horticultural industry, in regards to table grape production, has been significantly affected by both domestic and regional policies, as well as by the WTO rules. The aim of this study is to determine the environmental factors that create a competitive advantage for the Namibian table grape industry in the international market. A detailed supply-chain analysis, augmented by Porter’s ‘diamond’ model, is used in this study to assess the determinants of the competitiveness of fresh table grapes. Interviews were conducted in informal, semi-structured questions. The questionnaires were mailed to several producers within the table grape-growing industry. Secondary information was obtained from reports, articles and research publications, among other sources. An expert assessment was used to verify information based on the reference methods. Consultations took place in the form of office visits and, in some cases, telephone interviews were held with different experts. The finding of the study shows that Namibia can supply the European markets during the northern hemisphere off-season with quality fresh table grapes. However, industry growth in the European Union (EU) market is constrained by limited free import quotas and high tariffs, specifically as regards seeded fresh table grapes, which are not exempt from such duties. Such constraints are in place despite Namibia’s meeting of international set quality standards, such as EUREPGAP. Moreover, there is potential for increasing supplies to the regional and Asian markets as well as the US market albeit to the lesser extent. Finally, Namibian fresh table grapes profitability is significantly affected by the high production and transaction costs incurred, as well as by the decline in business and the depreciation of the US Dollar against the Namibian Dollar. The study makes the general recommendation that producers should significantly reduce their transaction costs within the chain, by means of vertical co-ordination and integration. / AFRIKAANSE OPSOMMING: Met die verklaring van Namibië se onafhanklikheid van Suid-Afrika in 1990 het die Namibiese regering hulle dit ten doel gestel om ontwikkelingsprogramme te beplan en in werking te stel ten einde daardie land se groeiende landbousektor te versterk. Die nuwe regering moet tans uitdagings met betrekking tot inkomsteongelykhede en die toekenning en verspreiding van hulpbronne die hoof bied wat tot die inwerkingstelling van grondhervormingsprogramme aanleiding gegee het. Internasionaal is Namibië 'n lidland van verskeie handelsreëlings soos die Wêreldhandelsorganisasie (WHO), die Suider-Afrikaanse Ontwikkelingsgemeenskap (SAOG) en die Suider-Afrikaanse Doeane-unie (SADU). Die twee hooffaktore wat daartoe gelei het dat Namibië hom by die internasionale gemeenskappe skaar, is marktoegang en handelsbeleidhervormings. Die land se landbousektor, in besonder die tuinboukundige bedryf met die klem op tafeldruifproduksie, is aansienlik deur binnelandse en streeksbeleid asook deur die WHO-reëls geraak. Die doel van hierdie studie is om die omgewingsfaktore te bepaal wat in die internasionale mark aan die Namibiese tafeldruifbedryf 'n mededingende voordeel gee. Derhalwe gebruik die navorser 'n gedetailleerde aanvoerkettingontleding, ondersteun deur Porter se “diamantmodel”, om die beslissende faktore vir die mededingendheid van vars tafeldruiwe te evalueer. Onderhoude is met behulp van informele, semigestruktureerde vrae gevoer. Die vraelyste is aan verskeie produsente op die gebied van tafeldruifboerdery gepos. Sekondêre inligting is ook onder andere uit verslae, artikels en navorsingspublikasies verkry. Met behulp van 'n kundige evaluering is inligting op grond van die verwysingsmetodes geverifieer. Oorlegpleging met verskeie kundiges het in die vorm van kantoorbesoeke en in sommige gevalle deur middel van telefoononderhoude plaasgevind. Die studiebevinding toon dat Namibië die Europese markte gedurende die noordelike halfrond se tussenseisoen van gehalte- vars tafeldruiwe kan voorsien. Die uitbreiding van die bedryf in die Europese Unie (EU-) mark word egter deur beperkte gratis invoerkwotas en hoë tariewe aan bande gelê, in besonder met betrekking tot pitlose, vars tafeldruiwe wat nie van invoerbelasting vrygestel is nie. Hierdie beperkinge word opgelê ten spyte daarvan dat Namibië aan vasgestelde internasionale gehaltestandaarde soos EUREPGAP voldoen. Die moontlikheid bestaan boonop om lewering aan die streeks- en Asiatiese markte asook die VS-mark te verhoog, hoewel in 'n mindere mate. Laastens word die winsgewendheid van Namibiese vars tafeldruiwe beduidend deur hoë produksie- en transaksiekoste, asook deur die afname in sake en die waardevermindering van die Amerikaanse teenoor die Namibiese dollar geraak. Die studie maak die algemene aanbeveling dat produsente hulle transaksiekoste binne die ketting aansienlik met behulp van vertikale koördinering en integrasie moet verminder.

Call number: LD2668 .T4 1986 H63 / Master of Science / Horticulture, Forestry, and Recreation Resources

Water resources for outdoor areas, such as lawns and landscapes, continues to become limited in many urban areas, especially in times of acute drought stress. Lawn species selection and cultural practices, such as mowing height, can strongly influence overall seasonal water needs. While previous research has reported various lawn species water use rates and differences in the ability of some cultivars to maintain green coverage during acute drought stress, little is known regarding the irrigation requirements of cool-season lawn species when using a deficit irrigation strategy based on a green coverage target threshold (e.g. 60-80% green) approach. Two greenhouse studies were conducted to screen various candidate species and seed mixtures in a sandy media. The highest water use and worst appearance/green coverage was associated with an inexpensive commercial lawn mixture; and the lowest water use and best appearance was generally associated with improved Kentucky bluegrass (<i>Poa pratensis</i> L.: KBG) cultivars. Field studies were conducted to quantify the irrigation requirements of drought susceptible (DS) and improved, drought tolerant (DT) KBG and tall fescue [<i>Schedonorus arundinaceus</i> (Schreb.): TF] cultivars, blends and mixtures at two mowing heights (5.1 or 8.9 cm). Results from a 74-day field study using a deficit irrigation replacement approach with a 70% green coverage threshold (GCT₇₀) irrigation trigger, demonstrated water savings of approximately 73 to 78% when using a DT TF (60.3 mm) as compared to 100% evapotranspiration (ET­_o) replacement (223.4 mm) and a conventional lawn irrigation approach (268.5 mm), respectively. The time to reach the GCT₇₀ generally ranked: TF=TF:KBG mixture>KBG and ranged from 18.0 days for DS ‘Right’ KBG and 52.5 days for DT ‘RainDance’ TF. Among TF and KBG cultivars using the GCT­₇₀irrigation approach, DT TF required 35 to 68% less supplemental irrigation compared to DT and DS KBG cultivars (92.1 vs. 187.3 mm), respectively. Within KBG cultivars, the DT ‘Desert Moon’ required one-half the irrigation of DS Right (92.1 vs. 187.3 mm), while there were no differences among TF cultivars for irrigation needs. Mowing height did not affect KBG irrigation needs, but TF at 5.1 cm showed increased visual quality and green coverage, and significantly reduced irrigation requirements. Field research also compared species mixtures and blends using DS and DT KBG and TF to determine the amount of a DT species/cultivar that would enhance drought performance with ratios ranging from 25-100% DT as well as 90:10 TF:KBG mixtures. The quantity of a DT KBG in a blend, and DT TF in a TF:KBG mixture reduced irrigation needs, whereas the drought rating of the KBG cultivar in a TF:KBG mixture had no significant effect. In summary, these studies continue to demonstrate that significant supplemental lawn irrigation savings can be achieved by the selection of superior DT species and cultivars combined with a deficit irrigation replacement approach compared to other cool-season species and conventional irrigation practices.

Avocados are an important horticultural crop in South Africa, especially in the provinces of KwaZulu-Natal, Mpumalanga and Limpopo. The distance to traditional export markets, phytosanitary restrictions to lucrative markets such as China, the USA and Japan and increased competition in the European market have challenged the South African avocado industry. The industry has responded with improved logistics and shipping, a co-ordinated market access program and a global system to co-ordinate exports of avocados to the European market. To remain competitive on the global market, further improvements and innovations are required to improve the efficiency of postharvest operations. These improvements and innovations should be guided by a greater understanding of postharvest physiology. Avocados are a relatively new export crop, so there is still much to be learnt about avocado postharvest physiology and the optimisation of postharvest management. In this regard, reduced temperature storage (1°C) and modified humidity packaging (MHP) were investigated for their effect on fruit physiology and quality, the effect of a water- and ABA-infusion on ripening was examined and the effect of a cold chain break on fruit physiology and quality determined; near-infrared spectroscopy was also examined for its potential for its use in the avocado industry. As an initial study, the relationships between individual sugars, protein and oil were studied to understand the changes in avocado fruit during ripening. It was found that mannoheptulose and perseitol were the predominant sugars at harvest, but declined to very low levels during the first 10 days postharvest. The concentrations of glucose and fructose increased, while sucrose declined slightly during ripening. The concentration of protein increased sigmoidally during ripening, reflecting the increase in the ripening enzymes, particularly cellulase and polygalacturonase. The oil content fluctuated slightly during ripening. It is suggested that mannoheptulose and perseitol are important carbon and energy sources during ripening. Glucose concentration was also found to increase earlier in fast ripening fruit compared to slow ripening fruit, which is related to increased cellulase activity and may be related to the ABA functioning. Thereafter, storage and ripening trials in two consecutive seasons showed that 1°C storage and the use of MHP for 28 days reduced mass loss, water loss, ethylene production, respiration, softening and heptose consumption, without appreciably affecting fungal rots, physiological disorders or external chilling injury, compared to fruit stored at 5.5°C and regular atmosphere respectively. Also, the storage of fruit in MHP delayed the rise in the activity of cellulase during ripening, compared to fruit not stored in MHP, but there was no significant difference in the peak activity of cellulase, polygalacturonase or pectin methylesterase. In a separate experiment, fruit ripening was significantly affected by the infusion of ABA in an aqueous solution. Water slightly reduced the variation in ripening while ABA reduced the time to ripening and the variation; it is suggested that water stress and ABA are intrinsically involved in the ripening processes and may act as a ripening trigger. The water concentration in fruit was measured non-destructively using reflectance NIR; this model was used to determine the maturity of fruit and the loss of water during cold storage. In the cold chain break experiment, it was found that although fruit recovered after a cold chain break, in terms of ethylene production and respiration, there was a loss in quality because of severe shrivelling as a result of increased water loss. Fruit that were stored at 1°C were generally of a better quality at ripeness, if the cold chain was broken, compared to fruit stored at 5.5°C. In a follow-up experiment, it was found that significant changes occurred in avocado physiology over a 6h period. The respiration rate of fruit significantly increased after 4h at room temperature and mannoheptulose declined by 32% in control fruit and by 16% in ethephon-treated fruit after 6h. This demonstrates the potential for quality loss in a short amount of time. Furthermore, a model of avocado ripening is proposed, outlining the role of water, ABA, ethylene, respiration, ripening enzymes and individual sugars. This study has contributed to the understanding of avocado postharvest physiology and should aid in better management of avocados for improved fruit quality and consumer satisfaction. / Thesis (Ph.D.Agric.)-University of KwaZulu-Natal, Pietermaritzburg, 2011.

Moving products is a costly exercise for most companies in South Africa. These high logistics costs impede the country from achieving some developmental goals such as creating more jobs and growing the economy. The horticulture sector is particularly ham-strung by this. Small business is more severely affected than big business. There are numerous, multi-faceted reasons for these high costs. The analysis and potential solutions are drawn from New Institutional Economics theory, political economy thinking, business process applications and economic geography thinking. It is clear that the solution goes beyond what is normally advocated by institutions that have done work in this area, e.g. the World Bank, which tends to focus on infrastructure investment. Issues typically overlooked that need greater attention include improving competition in the logistics sector and firm collaboration. Policy choices would have to be based on an understanding of the cyclical nature of some cost drivers (e.g. fuel costs) and the structural nature of some cost drivers (e.g. infrastructure) / Thesis (M.Dev.Studies)-University of KwaZulu-Natal, Durban, 2010.

The South African avocado industry is export-orientated with forty percent of total production sold overseas. The avocado fruit is a highly perishable product with a relatively high rate of respiration which results in the quick deterioration of fruit quality. Good phytosanitary procedures are a necessity in ensuring good product quality. Due to the threat of pests and diseases becoming resistant to the conventional chemicals currently used to control them, there has been a great need to diversify from their usage. Silicon (Si), being the second most abundant element (28%) in the earth’s crust after oxygen, is a major constituent of many soils and has been associated with disease resistance in plants for a long time. It has been used in a number of crop species to provide resistance against pathogenic agents. In some horticultural crops Si has been found to offer protection against fungal infections by strengthening cell walls, thus making it more difficult for the fungi to penetrate and colonize the plant. The aim of this research was to investigate the effects of postharvest silicon application on the quality of ‘Hass’ avocado fruit. The specific objectives included investigating the effect of silicon on the ripening pattern as well as the metabolic physiology of the avocado fruit. Avocado fruit were obtained from two locations in the KZN Midlands (Everdon Estate in Howick and Cooling Estate in Wartburg). Fruit were treated with different forms of Si (potassium silicate (KSil), calcium silicate (CaSil), sodium silicate (NaSil) and Nontox-silica® (NTS)) at concentrations ranging from 160 ppm to 2940 ppm. After dipping for 30 minutes in the silicon treatments, the fruit were stored at -0.5°C, 1°C, 5°C or at room temperature (25°C). Energy dispersive x-ray (EDAX) analysis was then conducted on the exocarp and mesocarp tissues to determine the extent of silicon infiltration within each treatment. Firmness measurements, ethylene evolution and CO2 production were recorded as fruit approached ripening. The CO2 production of fruit that were stored at room temperature was analysed daily until they had fully ripened, while fruit from cold storage were removed weekly to measure respiration. Mesocarp tissue from each fruit was extracted using a cork borer and subsequently freeze-dried and stored for physiological analysis. The freeze-dried mesocarp tissue was then finely ground and later analysed for sugar content, total anti-oxidant capacity (TAOC), total phenolic (TP) content and phenylalanine ammonia lyase (PAL) activity using their respective assays. Statistical analyses were carried out using GenStat® version 11 ANOVA. Treatment and storage temperature means were separated using least significant differences (LSD) at 5% (P = 0.05). The experimental design in this study was a split-plot design with the main effect being storage temperature and the sub-effect being treatments. Each replication was represented by a single fruit. EDAX analysis revealed that Si passed through the exocarp into the mesocarp tissue in fruit treated with high concentrations of silicon, i.e., KSil 2940 ppm. Significant differences (P < 0.001) were observed in temperature means with regards to firmness. Fruit treated with KSil and NTS only and stored at 5°C were firmer than fruit stored at other temperatures. Fruits treated with Si in the form of KSil 2940 produced the least amount of CO2, while non-treated fruits (Air) had the highest respiration rate. Fruit stored at room temperature (25°C) produced significantly higher amounts of CO2 and peaked much earlier than fruit stored at other temperatures. Ethylene results showed that there were differences (P < 0.05) between temperature means with the highest net ethylene being produced by fruit stored at 25°C. There were also significant differences amongst treatment means (P < 0.001), with fruits treated with KSil 2940 ppm producing the least ethylene. There were significant differences (P < 0.001) in temperature means with regards to the total phenolic concentration with fruits stored at 1°C having the highest TP concentration (26.4 mg L-1 gallic acid). Fruit treated with KSil 2940 ppm had the highest total phenolic concentration whilst the control fruit (Air and Water) had the lowest. There were also differences (P < 0.05) in storage temperature means with respect to the total antioxidant capacity. Fruit stored at -0.5°C had the highest TAOC (52.53 μmol FeSO4.7H2O g-1 DW). There were no significant differences in TAOC (P > 0.05) with regards to treatment means although fruit treated with KSil 2940 ppm and stored at -0.5°C showed the highest TAOC of 57.58 μmol FeSO4.7H2O g-1 DW. With regards to the concentration of major sugars in avocado, mannoheptulose and perseitol (mg g-1), no significant differences (P > 0.05) were observed in temperature means. However, fruit stored at -0.5°C had the highest concentration of these C7 sugars compared with fruit stored at other temperatures. There were significant differences in treatment means (P < 0.001) showing that fruit treated with KSil 2940 ppm had the highest concentration of both mannoheptulose (18.92 mg g-1) and perseitol (15.93 mg g-1) in the mesocarp tissue. Biochemical analyses showed differences (P < 0.05) in storage temperature means with respect to PAL enzymatic activity. Fruit stored at 5°C had the highest PAL activity (18.61 mmol cinnamic acid g-1 DW h-1) in the mesocarp tissue compared with fruit stored at other temperatures. There were significant differences in treatment means (P < 0.001) with regard to PAL activity. Fruit treated with KSil 2940 ppm had the highest PAL activity (23.34 mmol cinnamic acid g-1 DW h-1). This research has demonstrated the beneficial effects, particularly applications of 2940 ppm Si in the form of KSil. This treatment successfully suppressed the respiration rate of avocado fruit. Biochemical analyses of total antioxidants, total phenolics and PAL activity in the mesocarp tissue have shown the usefulness of Si in improving the fruit’s metabolic processes. The C7 sugars (D-mannoheptulose and perseitol) also seem to be more prevalent in avocado fruit treated with Si (particularly KSil 2940 ppm) than in non-treated fruit. This suggests that an application of Si to avocado fruit can aid in the retention of vital antioxidants (C7 sugars). / Thesis (M.Sc.Agric.)-University of KwaZulu-Natal, Pietermaritzburg, 2010.

Cabbage is one of the most important and widely grown crops in KwaZulu-Natal (KZN). In cabbage production, no clear cropping methods exist (other than succession cropping) to allow the soil to recover its fertility status naturally after the harvested has crop absorbed nutrients from the soil. Succession cropping system is extensively practiced by cabbage farmers. Succession cropping is when a succeeding vegetable crop is planted immediately after harvesting the preceding crop. This does not allow soil fertility status to be balanced by soil microbes in an environmentally friendly approach. Instead, synthetic fertilizers are heavily used to rectify soil fertility status and these have negative impacts on the soil in the long term, followed by yield decline. However, the economic downturns and green environment awareness have caused researchers and some farmers to focus more on developing environmentally healthy crop production technologies. A priority in this study was to elucidate effects of cover crops-green manure as rotational crops in cabbage production. The experimental site is located at Cedara Research Station. In 2009, soil samples were taken from the top 30 cm of the soil profile, in a zigzag pattern in 5 m x 5 m grids for fertility analysis. Results were used to determine nutrient deficiencies, and blanket application of phosphorus and potassium followed according to each grid’s deficiency. The study was divided into two cycles, with each cycle consisting of season one and season two. The study was conducted over a two year period. Cycle one, season one, 2009/2010 (Dec-Mar): four treatments (sunn hemp: planted at 50 kg/ha seeding rate; forage sorghum: planted at 50 kg/ha seeding rate; mixture of sunn hemp-forage sorghum: each planted at 25 kg/ha seeding rate and control: cabbage planted at 30 cm within rows x 60 cm between rows) were used. The statistical design of the study was a 4x4 Latin Square experiment repeated twice in adjacent fields (347 m2 each) 6 m apart, with a total of 32 plots. Each experimental plot was 8.5 m x 9 m. Genstat Package, 9th Edition was used for data analysis. Standard cabbage production recommendations were followed in control treatments. Cabbage yield was determined in all control plots. Weed coverage percentages were determined in all four treatments. Cycle one, season two, 2010, (Apr-Aug): all 32 plots from season one were each split into four, in a Split Plot design, resulting in a total of 128 plots in both fields. Nitrogen was applied at four different levels: 0, 80, 160 and 240 kg N/ha. Standard cabbage production methods were followed again as in the control treatment in season one. Cover crops were replaced by planting cabbage. Cabbage was repeated in the control plots. Cabbage yield, cabbage leaf nutrients, soil nitrate and ammonium nitrate and soil carbon to nitrogen (C:N) ratio were measured. Cycle two, season one, 2010 (Sep-Dec): The same method in cycle one, season one was repeated. Cycle two, season two, 2010/2011, (Dec-Apr): The same method in cycle one, season two was repeated. Although in this study there was visibly a large amount of residues left over after the trial was harvested, the use of a tractor-drawn slasher was not very effective. The slashed material was not chopped into smaller pieces, as it would if a roll-chopper had been used. A tractor-drawn slasher was used because it is a tool available to many farmers. As a result, it was not a simple process to transplant seedlings mechanically, due to the amount of organic matter that was in the soil after it had been incorporated. The mechanical planter pulled off, removed and became blocked by the residues, and as a result it was not able to operate as it would in normal soils. The residues removed soil from the furrows and that caused seedlings to fall over as all the soil for the root system support had been moved by the planter and stuck residues. The planter had to be assisted by hand planting seedlings that were not properly planted mechanically. Hence, from the operational perspective, the choice of tools for chopping were not effective in this study and this is something to be considered in future studies, where it will be necessary to compare different tools for planting and cover crop incorporation into the soil. During the present study, soil N content in different plots had significant differences (P=0.05). The control showed high levels of total N content, but this was not related to the low yields exhibited by cabbage after cabbage at all levels of N. Since, where there were cover crops, the N content was low, this could mean that N was immobilized, compared to the cabbage treatments where plenty of N was available. Immobilized N is thus not available for leaching, polluting the environment. The yield of cabbage was significantly lowest in controls. The study showed that cover crop-green manure use has a positive effect in terms of yield improvement. The cabbage yields from the sunn hemp plots at a 0 kgN/ha were significantly different from the yield of cabbage planted following cabbage at 240 kgN/ha N. The study also showed that N is not the only yield determinant in cabbage production. Too much N has a tendency to suppress cabbage yields. The cover crop-green manures selected for this study were shown to be ineffective in suppressing weeds. This was true even though the weed coverage percentage in each of the cover crop-green manure plots was above 65%, except for the cabbage crop. This study did not separate different weeds, but the most dominant weeds were Amaranthus hybridus (pigweed), Galinsoga parviflora (gallant soldier), Bidens pilosa (common blackjack) and Cyperus esculentus (yellow nutsedge). These weeds were effectively controlled in the cabbage sole crop by the use of herbicides and mechanical weeding. The result of cover crop-green manures not suppressing weeds was significantly associated with the cover crop-green manure seeding rate. This study has been a starting point in the development of cover crops-green manure as rotational crops in cabbage production. It is concluded that cover crop-green manure (sunn hemp and forage sorghum) used in this study for vegetable (cabbage) production has proven to be successful in improving yields. Yields obtained from cover crop-green manure treatments were better than yields obtained from - conventional tillage methods for cabbage production (control). However, in cabbage, weed suppression and soil N content, failed to improve significantly in response to the cover crop green manures used. The high plant population density under a cover crop, combined with weed population, may lead to high uptake of soil N for plant growth, leaving less N in the soil and in the plant. In the sole cabbage crop, because of low competition, there was adequate uptake of N for plant growth and yet the crop was not exhaustive of soil N. Further research is required in the following areas: comparison of cabbage with other vegetable crops in response to the effect of the selected cover crops; comparison of mechanical weeding and herbicide use as means of controlling weeds during cover crop-green manure growth; identification of dominant weeds in the presence and absence of cover crops, and monitoring of soil water relations and other fertiliser effects. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2012.

Most tomato cultivars used for commercial food production are imported into South Africa. Optimal growing conditions for these specific cultivars need to be determined, as wrong cultivar choices can lead to great financial losses. Lack of information on selecting well-performing cultivars may lead to lower yield or unacceptable fruit quality. Information on the performance of tomato cultivars under South African conditions, utilizing plastic tunnels or shadenet structures under soilless cultivation is still very limited. Soilless cultivation of vegetables is becoming a preferable over in-soil cultivation due to the improved yield and quality of produce, efficient water and nutrients usage by the crop; furthermore, the grower can regulate nutrient solution, electrical conductivity and pH of the nutrient solution. To identify the optimal system for growing tomatoes hydroponically, the performance of four tomato cultivars (‘FA593’, ‘Miramar’, ‘FiveOFive’ and ‘Malory’) under different growing conditions was evaluated: directly planted in soil under 40% shadenet with drip irrigation, a closed hydroponic system under 40% shadenet, an open bag system under 40% shadenet, or an open-bag system in a temperature controlled as well as a non-temperature controlled tunnel. The study revealed that ‘Miramar’ performed better than the other cultivars in all production systems, with the exception of soil cultivation where there were no differences amongst the four cultivars. Fruit cracking was found to be directly correlated with fruit size, as the large-sized cultivars ‘Malory’ and ‘FA593’ were more susceptible than the other two cultivars. Plants grown under shadenet were prone to fruit cracking and raincheck as well as early blight. Higher yields were obtained when plants were produced in the open bag system under temperature controlled conditions and in the closed system under shadenet. Growing tomatoes in the non-temperature controlled tunnel resulted in high incidences of fruit cracking, poor yield and pre-mature fruit ripening probably due to high and fluctuating temperatures under such conditions. The average marketable yield was 88% and 59% of the total yield in the temperature controlled and non-temperature controlled tunnels, respectively. A further experiment was carried out to improve yield and quality of tunnel tomatoes using beneficial micro-organisms, i.e., arbuscular mycorrhiza fungi (AMF) at different nutrient concentrations. Tomato seedlings were treated with Mycoroot™ containing four mycorrhiza species (Glomus etunicatum, Paraglomus occultum, Glomus clarum and Glomus mossea) at transplanting and subsequently transferred to either a temperature controlled or a non-temperature controlled tunnel under the recommended (100%) or reduced (75 and 50%) nutrient concentrations. Sawdust was used as a growing medium in this experiment. Application of AMF neither enhanced plant growth, yield, nor fruit mineral nutrient concentrations; although fruit Mn and Zn concentrations in the temperature controlled tunnel increased significantly following AMF application. Plants grown in the non-temperature controlled tunnel had significantly poorer plant growth, and lower yield and lower fruit mineral concentrations, compared with fruit from plants in the temperature controlled tunnel. Tomato plants in the non-temperature controlled tunnel had higher levels of micro-elements in leaf tissue, compared with those in the temperature controlled tunnel. The highest yields were obtained from plants fertigated with 75% of the recommended nutrient concentration, as compared with the 100 and 50% nutrient concentrations. When coir was subsequently used as the growing medium, Mycoroot™ applied at seeding and transplanting did not enhance mycorrhizal colonization or fruit quality. Growing tomatoes under reduced nutrient supply reduced the total soluble solids in the juice of the fruit, but improved total and marketable yield, as well as the number of marketable fruit. This effect was more substantial in the temperature controlled than in the non-temperature controlled tunnel. Fruit firmness and leaf chlorophyll concentrations were significantly higher in plants grown in the temperature controlled tunnel. Growing tomatoes in sawdust improved the leaf Mn and Ca concentration over that of tomato plants grown in coir. Mycorrhizal colonisation did not have a beneficial effect on tomato yield and quality. The study indicated that cultivar selection was important in obtaining the highest yield and quality of tomato using the closed hydroponic system under shadenet and the open bag hydroponic system in the temperature controlled tunnel. Temperature controlled tunnels with a pad–and-fan cooling system are still an effective way of cooling the tunnel environment which resulted in high yield and high quality of tomatoes with a higher fruit mineral content than that obtained under non-temperature controlled conditions where only natural ventilation is relied on. Results also demonstrated that mycorrhizal colonization in soilless condition has limited beneficial effects in allowing for better nutrient uptake and thereby for improved yield and quality of tomatoes. Further studies, including different media, nutrient composition and concentrations, need to be carried out to investigate the possible causes of AMF failure to improve yield, despite good AMF root colonization. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2013.