Thesis (MScAgric)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Olives have been produced commercially in the Mediterranean-type climate of the Western Cape region of South Africa since the early 1900’s. As in the rest of the world, South African table olive producers struggle with alternate bearing. Naphthalene acetic acid (NAA) has been used since the 1950’s to thin table olives in California. To date, South African producers opted to tolerate rather than try to reduce the negative effects of alternate bearing. However, due to increased olive production, profit margins are decreasing and producers can no longer ignore the negative effects of alternate bearing. Since the efficacy of NAA as a thinning agent is modulated by environmental conditions and genotype, trials were conducted to evaluate the use of NAA on locally important cultivars under South African conditions. The main aim was to establish optimum application rates for ‘Barouni’, ‘Mission’ and ‘Manzanillo’. NAA decreased the fruit number per tree, thereby improving fruit quality (increased fruit size and a higher proportion black fruit in the case of ‘Mission’) in all three cultivars. Thinning did not affect the return bloom in any of the cultivars. In the case of ‘Barouni’, the lack of a return bloom response could be due to the low level of thinning achieved, while climatic conditions during flower development may be to blame for the lack of response in ‘Mission’ and ‘Manzanillo’. Although NAA application did not affect the income per hectare, profitability may increase as harvesting costs account for roughly 50% of the input costs. Based on our results, NAA at 200 mg L-1, applied 10 to 15 days after full bloom, is recommended for local conditions. This concentration is slightly higher than the application rates used in California. An even higher NAA concentration might be used when premium prices are paid for large fruit, as in the case of ‘Mission’ and ‘Manzanillo’. However, NAA at 400 mg L-1 seemed to decrease vegetative growth in ‘Mission’, which may decrease bearing positions for the next season. Earlier application should be considered for a heavy “on” crop while the concentration can be decreased or the spray time delayed to decrease thinning when an average crop is anticipated. Gibberellic acid (GA3) was applied during an “off” season to ‘Mission’ and ‘Manzanillo’ to determine when during the season floral induction is inhibited by the simulated seed produced hormone. GA3 had its greatest effect on the extent of flowering in ‘Manzanillo’ when applied at the time of endocarp sclerification in early December. It follows from this result that to prevent the negative effects of a crop load on flowering in the subsequent season, thinning has to occur before endocarp sclerification. Later application of GA3 in January and February also decreased flowering, but to a lesser extent than application in December. These later applications possibly decreased flower initiation in buds on shoots that continued growing for longer or they may also have interfered with flower differentiation. The effect of the reduced “on” crop in the 2010/2011 season in GA3-treated trees on yield in the 2011/2012 season still needs to be determined. / AFRIKAANSE OPSOMMING: Olywe word sedert die vroeë 1900’s kommersieel geproduseer in die Mediterreense tipe klimaat Wes-Kaap streek van Suid Afrika. Soos in die res van die wêreld, is alternerende drag ‘n reuse struikelblok vir Suid-Afrikaanse olyfprodusente. Anders as in California waar naftaleenasynsuur (NAA) reeds vanaf die 1950’s gebruik word om tafel olywe uit te dun, het Suid-Afrikaanse produsente tot op hede die gevolge van alternerende drag verduur eerder as om die negatiewe effekte daarvan te probeer verminder. Weens ‘n afname in winsgewendheid vanweë ‘n toename in olyfproduksie kan Suid-Afrikaanse olyfprodusente egter nie meer langer die negatiewe effekte van alternerende drag ignoreer nie. Die effektiwiteit van NAA as uitdunmiddel word beïnvloed deur omgewingstoestande asook deur die plant se genetika. Gevolglik is proewe onderneem om die gebruik van NAA te evalueer op plaaslik belangrike kultivars en onder Suid-Afrikaanse kondisies. Die hoofdoel van die proewe was om optimale toediening konsentrasies van NAA vir ‘Barouni’, ‘Mission’ en ‘Manzanillo’ te bepaal. NAA het die vruglading per boom verminder en daardeur vrugkwaliteit (vruggrootte asook ‘n groter proporsie swart vrugte in die geval van ‘Mission’) in al drie kultivars verbeter. In al drie kultivars het uitdunning egter geen effek op die volgende seisoen se blom gehad nie. In die geval van ‘Barouni’ kan die swak opvolgblom moontlik toegeskryf word aan die lae vlak van uitdun terwyl klimaatstoestande tydens blomontwikkeling moontlik die oorsaak was vir die swak reaksie van ‘Mission’ en ‘Manzanillo’. Alhoewel toediening van NAA nie die bruto inkomste per hektaar verhoog het nie, kan winsgewendheid moontlik toeneem aangesien oeskoste ongeveer 50% van insetkostes uitmaak. Gebaseer op die resultate van die studie, word NAA toediening teen 200 mg L-1, 10 tot 15 dae na volblom, aanbeveel vir plaaslike toestande. Hierdie konsentrasie is effens hoër as konsentrasies wat in Kalifornië gebruik word. Selfs hoër NAA konsentrasies kan toegedien word wanneer ’n premium betaal word vir groter vrugte, soos in die geval van ‘Manzanillo’ en ‘Mission’. NAA teen 400 mg L-1 het egter vegetatiewe groei in ‘Mission’ verlaag en dit kan moontlik lei tot ‘n vermindering in draposisies in die volgende seisoen. Vroeër toediening moet oorweeg word wanneer ‘n groot “aan” oes verwag word, terwyl die NAA konsentrasie verminder of toediening uitgestel kan word ten einde uitdunning te verminder indien ‘n gemiddeld oes verwag word . Gibberelliensuur (GA3) is in die “af” seisoen toegedien op ‘Mission’ en ‘Manzanillo’ om vas te stel wanneer gedurende die seisoen saad-geproduseerde hormone blominduksie inhibeer. Die grootste effek op blominduksie van ‘Manzanillo’ is verkry met toediening tydens pitverharding gedurende vroeë Desember. Om die negatiewe effek van ‘n hoë vruglading op die volgende seisoen se blom te voorkom, moet vruguitdunning dus voor pitverharding geskied. Later toediening van GA3 in Januarie en Februarie het ook blom verminder, maar tot ‘n mindere mate as toediening in Desember. Hierdie later toedienings het moontlik blominisiasie van knoppe wat later gevorm het geïnhibeer of kon moontlik blomdifferensiasie negatief beïnvloed het. Die effek van die verlaagde “aan” jaar in die 2010/2011 seisoen in reaksie op GA3 toediening op opbrengs in die 2011/2012 seisoen moet nog bepaal word.

<p>Cape Town includes two vegetable farming areas within the city limits, the Joostenbergvlakte/Kraaifontein area and the Philippi area. Both areas supply produce to local markets and further afield. Sporadically, high levels of cadmium, copper, lead and zinc have been found to occur in some of the soils, irrigation water resources and crops. To find the sources of specifically Cd, Pb and Zn to these agricultural systems, extensive analysis of several heavy metals in inputs such as fertilizers, agrochemicals and supplementary water resources to these farming areas was undertaken. Heavy metal concentrations in soils, irrigation water resources and crops were also determined. Two mitigation techniques that could be used to remediate Cd, Pb and Zn contamination were investigated. The first mitigation method included immobilization of heavy metals as phosphate complexes by using a triple super phosphate fertilizer, while the second method involved mobilisation and thus leaching of heavy metals away from plant roots using EDTA. These mitigation methods were tested in a pot experiment using cabbage as the experimental crop and soil from these areas as growth medium. A survey of common farming practices in these two areas and farmers willingness to use remediation methods was conducted.</p>

<p>Cape Town includes two vegetable farming areas within the city limits, the Joostenbergvlakte/Kraaifontein area and the Philippi area. Both areas supply produce to local markets and further afield. Sporadically, high levels of cadmium, copper, lead and zinc have been found to occur in some of the soils, irrigation water resources and crops. To find the sources of specifically Cd, Pb and Zn to these agricultural systems, extensive analysis of several heavy metals in inputs such as fertilizers, agrochemicals and supplementary water resources to these farming areas was undertaken. Heavy metal concentrations in soils, irrigation water resources and crops were also determined. Two mitigation techniques that could be used to remediate Cd, Pb and Zn contamination were investigated. The first mitigation method included immobilization of heavy metals as phosphate complexes by using a triple super phosphate fertilizer, while the second method involved mobilisation and thus leaching of heavy metals away from plant roots using EDTA. These mitigation methods were tested in a pot experiment using cabbage as the experimental crop and soil from these areas as growth medium. A survey of common farming practices in these two areas and farmers willingness to use remediation methods was conducted.</p>

The influence of crude oil-contaminated and remediated sites on agrifood production is not clearly understood. To address this knowledge gap, the research was divided into two stages involving: (1) assessment of the efficiency of two bioremediation strategies to support hydrocarbons degradation as well as agrifood production with the initial analysis of the experimental materials, and (2) evaluation of the effect of different crude oil remediation intervention values (CRIV) on selected vegetables (Brassica juncea, Brassica oleracea, Lactuca sativa and two different cultivars of Solanum lycopersicum). Results from the first stage showed that the crude oil used had a pristane/phytane ratio of 0.98 (within the 0.8 – 3.0 range of most crude oils), higher concentrations of C10 – C14, C15 – C20 and C21 – C27 alkanes than the C28 – C36 alkanes including higher concentrations of two of the US EPA priority pollutant polycyclic aromatic hydrocarbons (PAHs) - phenanthrene and anthracene. Four treatments were prepared in which weekly tillage enhanced the degradation of C15 – C20 and C21 - C27 alkanes in the Remediation by Enhanced Natural Attenuation (RENA) treatment. The two bioremediation strategies (RENA and bioaugmentation) enhanced PAHs degradation compared with the remediation-study control treatment while only RENA application among the two approaches supported the growth of B. juncea. Although there was no statistical significant difference (p > 0.05) between the major dietary mineral contents of samples from the various treatments compared with the control treatment samples, RENA application affected the Cr, Zn and Pb contents. Meanwhile, the Ca/P (> 1.0) and Na/K (< 0.60) ratios of all the harvested samples imply that they provide a good source of these minerals for bone formation and would not contribute to high blood pressure. The crude oil used also deterred the attack of juvenile caterpillars of cabbage white butterfly. Findings from the second stage revealed that the yield of the green leafy vegetables including one of the selected tomato cultivars (Micro-Tom), was in most cases impaired at CRIV ≥ 3,000 mg/kg total petroleum hydrocarbon (TPH). Compared with the control treatment samples’ composition, crude oil stress at 10,000 mg/kg TPH enhanced the concentration of K, Mn and crude protein of B. oleracea and L. sativa as well as the sucrose, total sugars, total phenolics and total flavonoids contents of the latter vegetable. Sucrose was also only detected in M82 tomato cultivar samples from the crude oil-containing treatments. The Cd content of B. oleracea, Pb contents of: L. sativa and M82 tomato harvested samples were all below the FAO/WHO Codex Alimentarius Commission 2015 recommended maximum levels. However, tartaric acid was only detected in B. oleracea and L. sativa samples from the 10,000 mg/kg TPH treatment as well as in M82 tomato cultivar samples from the treatment involving CRIV of 5,000 mg/kg TPH. Generally, the yield of these crops in response to crude oil contamination varied in which B. juncea had the least tolerance to crude oil stress among the green leafy vegetables tested. Most of the quality parameters in the two tomato cultivars were not affected by CRIV between 750 - 5,000 mg/kg TPH with p-xylene having the greatest toxic potential among the VOCs emitted from the 5,000 mg/kg TPH treatment. The research findings, under the experimental conditions, indicated the effectiveness of RENA for the degradation of low molecular weight PAHs and its agricultural benefits. They also suggest that crude oil-contaminated sites at ≤ 3,000 mg/kg TPH present a similar growing environment to a clean site for agrifood production and the possibility that crude oil stress at 10,000 mg/kg TPH could enhance crop quality. Nonetheless, the contribution of bio- accumulated PAHs in these crops to the food chain demands further investigation.

Philosophiae Doctor - PhD / Cape Town includes two vegetable farming areas within the city limits, the Joostenbergvlakte/Kraaifontein area and the Philippi area. Both areas supply produce to local markets and further afield. Sporadically, high levels of cadmium, copper, lead and zinc have been found to occur in some of the soils, irrigation water resources and crops. To find the sources of specifically Cd, Pb and Zn to these agricultural systems, extensive analysis of several heavy metals in inputs such as fertilizers, agrochemicals and supplementary water resources to these farming areas was undertaken. Heavy metal concentrations in soils, irrigation water resources and crops were also determined. Two mitigation techniques that could be used to remediate Cd, Pb and Zn contamination were investigated. The first mitigation method included immobilization of heavy metals as phosphate complexes by using a triple super phosphate fertilizer, while the second method involved mobilisation and thus leaching of heavy metals away from plant roots using EDTA. These mitigation methods were tested in a pot experiment using cabbage as the experimental crop and soil from these areas as growth medium. A survey of common farming practices in these two areas and farmers willingness to use remediation methods was conducted. / South Africa

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