Thesis (MScAgric)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Glyphosate remains an important herbicide in weed control. This is due to several positive attributes it has including sytemicity, wide spectrum of weed control and environmental friendliness. Its efficacy and lack of residual activity are therefore important to ensure adequate weed control without imposing hazards to the environment. Despite these favourable attributes for weed control glyphosate has its shortcomings. Evolution of resistance to glyphosate has been a major concern from 1996. However, there are other factors that reduce the maximum potential of glyphosate. Any factors that reduce glyphosate efficacy may result in the target plant being subjected to non-lethal concentrations of glyphosate. This in turn may predispose the plants to developing herbicide resistance. Some factors that may influence efficacy of glyphosate, and therefore be possibly selecting for resistance were investigated in this study. Although glyphosate is a postemergence herbicide, its efficacy is not exempt from the effect of soil and nutrients in which the weeds occur. The possibility of this occurring was investigated in a greenhouse study on ryegrass (Lolium spp.) In this study ryegrass was grown in three soils: pure sand (SS), soil from pasture paddock (PS) and soil from crop field (CS). The soils varied in nutrient composition and, although all were classified as sand, they had varying proportions of sand, loam and clay. This investigation consisted of four experiments. The first experiment was investigating the effect of growing a susceptible commercial ryegrass cultivar on PS, CS and SS soils on the efficacy of glyphosate (360 g a.i. L-1 formulation) applied at five glyphosate application rates (GAR). The GARs were 0 (0x), 67.5 (1/8x), 135 (1/4x), 270 (1/2x) and 540 (1x) g a.i. ha-1. The second experiment investigated the effect of growing a susceptible commercial ryegrass cultivar and a glyphosate resistant ryegrass biotype on PS and CS soils on the efficacy of glyphosate. The application rates were 0 (0x), 270 (1/2x), 540 (1x), 1080 (2x) and 2160 (4x) g a.i. ha-1. The third and the fourth experiments were similar to the first experiment except: The latter investigated the role of nutrient content of irrigation water (pure water or balanced nutrient solution) and; the former investigated the effect of soil activity (by covering the soil surface with cotton at the time of spraying) of glyphosate with regard to the role it plays on efficacy of glyphosate. Our findings showed that: i) soil affects the efficacy of glyphosate with more control (19% survivors) found in the PS soil compared to 50% and 62% survivors in CS and SS soils respectively, this effect may be dependent upon the species resistance as; ii) the effect in the resistant ryegrass biotype was reversed with about 95% of survivors in the PS soil compared to about 78% in CS soil; iii) efficacy of glyphosate is influenced by the soil nutrient status and the nutrient content of the irrigation water. This was shown by decrease in the control of ryegrass (100% survivors) grown in SS soil when fed with pure water compared to 45% when nutrient fed. In PS soil there was no significant effect. This was probably due to inherently higher nutrient content of the PS soil; and iv) glyphosate efficacy is influenced by the amount of glyphosate reaching the soil (absorbed through the roots). This was shown in PS soil where 1/8x GAR resulted in 93.3% survivors in covered soil compared to 60% in uncovered soil. A similar trend was also observed at 1/4x GAR. An opposite effect was shown in SS soil with 0% and 40% survival at 1/4x GAR in the covered and uncovered soil respectively. Glyphosate has been hailed as an environmentally friendly herbicide as it rapidly degrades in soil and it sorbs on metals embedded in soil matrix. However, reports in the literature have showed reduction in crop yield due to soil glyphosate residues. In these studies, glyphosate phytotoxicity was found to be dependent on certain soil characteristics and nutrient content. Following this, a greenhouse study was conducted to assess the phytotoxic activity of glyphosate on a susceptible commercial ryegrass cultivar grown in PS, CS and SS soils. Glyphosate was applied at 0 (G1), 540 (G2) and 3240 (G3) g a.i. ha-1. Ryegrass seedlings of comparable size were transplanted into the soil at intervals of two hours, three weeks and four weeks after glyphosate application referred to as TAS1, TAS2 and TAS3 respectively. Evidence of soil glyphosate activity was shown by the decrease in percentage survival with the application of glyphosate. This was significant in the SS soil where about 60% and 48% survival in G1 and G2 GAR respectively was observed compared to about 100% in the untreated control when transplanted three weeks after glyphosate application. The decrease in percentage survival was time mediated with significant effect of G2 GAR shown at TAS 1 whereas at G3 GAR the effect was significant at TAS1 and TAS 2. At TAS 3 there was no effect at all GARs. Similar trends were observed with dry mass and shoot length. Trace metals required for normal plant growth have been implicated in the reduction of glyphosate efficacy. This follows glyphosate’s original development as a metal chelator. Glyphosate-trace metal antagonism has recently sparked interest following co-application in glyphosate resistant soybeans. Molybdenum (Mo), an anion, may play a role at the physiological level on the antagonism of glyphosate. A greenhouse assay was carried out where seedlings grown from seeds (of susceptible commercial ryegrass cultivar (S biotype) and glyphosate resistant biotype (R biotype)) were grown with nutrient solutions containing 0x, 1x and 2x molybdenum (Mo) concentrations where 1x is 0.05 mg L-1 Mo. Glyphosate was applied at 0 (0x), 135 (1/4x), 270 (1/2x), 540 (1x) and 1040 (2x) g a.i. ha-1 rates. In the R biotype applying 2x Mo resulted in 0% survival in the R biotype at 1x GAR compared to 50% and 90% survival at the same GAR with 0x and 1x Mo. In terms of dry mass and shoot length the results did not show any conclusive trends. / AFRIKAANSE OPSOMMING: Glifosaat is ‘n baie belangrike onkruiddoder wat in verskeie onkruidbeheerstelsels gebruik word. Dit is as gevolg van verskeie positiewe eienskappe waaroor dit besit onder andere sistemiese werking, wye spektrum van onkruidbeheer en omgewingsvriendelike werking. Die onkruiddoder se effektiwiteit en gebrek aan residuele aktiwiteit is dus belangrik om bevredigende onkruidbeheer te bewerkstellig sonder om skade aan die omgewing te veroorsaak. Ten spyte van hierdie voordelige eienskappe het glifosaat ook tekortkominge. Vanaf 1996 is ontwikkeling van weerstand teen glifosaat in onkruide ‘n groot bron van kommer. Daar is egter ook ander faktore wat die maksimum potensiaal van glifosaat strem. Enige faktore wat die effektiwiteit van glifosaat strem mag veroorsaak dat die teikenplant aan subletale dosisse van glifosaat blootgestel word. Dit mag weer daartoe lei dat sulke plante blootgestel word aan die ontwikkeling van weerstand. Sommige faktore wat die effektiwiteit van glifosaat mag strem en dus moontlik kan lei tot seleksie vir weerstand is in hierdie studie ondersoek. Alhoewel glifosaat ‘n na-opkoms middel is kan die effektiwiteit moontlik beïnvloed word deur grondfaktore en nutriënte. Hierdie moontlikheid is ondersoek in ‘n glashuisstudie waarin raaigras (Lolium spp.) gebruik is. In hierdie studie is raaigras geplant in drie verskillende grondsoorte nl. suiwer sand (SS), grond vanaf ‘n weidingskamp (PS) en grond vanaf ‘n gewasland (CS). Die gronde het gevarieer in terme van nutriëntinhoud en alhoewel al drie gronde as sand geklassifiseer is, was daar tog verskille in fisiese eienskappe. Hierdie afdeling het uit vier eksperimente bestaan. In die eerste eksperiment is die invloed van verskillende gronde (PS, CS en SS) waarin die kommersiële raaigras kultivar geplant was op die effektiwiteit van glifosaat (360 g a.b. L-1 formulasie) teen vyf verskillende dosisse (GAR) ondersoek. Die dosisse was 0 (0x), 67.5 (1/8x), 135 (1/4x), 270 (1/2x) and 540 (1x) g a.b. ha-1. Die tweede eksperiment het die invloed van twee grondsoorte (PS en CS) waarin ‘n vatbare kommersiële raaigras kultivar en ‘n glifosaat weerstandbiedende raaigras biotipe geplant is, se invloed op die effektiwiteit van glifosaat ondersoek. Die dosisse was 0 (0x), 270 (1/2x), 540 (1x), 1080 (2x) and 2160 (4x) g a.b. ha-1. Die derde en vierde eksperimente was soortgelyk aan die eerste eksperiment behalwe dat die derde eksperiment die invloed van voeding (suiwer gedistileerde water teenoor ‘n gebalanseerde voedingsoplossing) saam met besproeiing ondersoek het. In die vierde eksperiment is die grondwerking van glifosaat wat as blaarbespuiting toegedien is ondersoek deurdat sommige potte wat gespuit is se oppervlakte met ‘n laag watte bedek is tydens die spuitproses en dadelik na spuit verwyder is teenoor die ander behandeling waar die grondoppervlakte nie bedek is nie. Die resultate het getoon dat i) grondtipe die effektiwiteit van glifosaat beïnvloed met beter beheer (19% oorlewing) in die PS grond vergeleke met 50% en 62% oorlewing in die CS en SS grondtipes respektiewelik. Hierdie effek kan moontlik beïnvloed word deur die weerstandsvlak van spesies omdat ii) die effek in die weerstandbiedende biotipe omgekeer is met ongeveer 95% oorlewing in the PS grondtipe vergeleke met 78% in die CS grondtipe; iii) effektiwiteit van glifosaat is beïnvloed deur die voedingstatus van die grond en die besproeiingswater. Dit word aangedui deur die afname in beheer van raaigras (100% oorlewing) wat in SS grond gegroei het en met suiwer gedistilleerde water besproei is vergeleke met 45% oorlewing in dieselfde grond wanneer met ‘n gebalanseerde voedingsoplossing besproei is. Plante wat in PS grond gegroei het het geen betekenisvolle verskille tussen die besproeiingsbehandelings getoon in hulle reaksie op glifosaattoediening nie, waarskynlik as gevolg van die inherente hoër nutriëntinhoud van die grond en iv) glifosaat effektiwiteit word beïnvloed deur die hoeveelheid glifosaat wat die grond bereik en deur die wortels opgeneem word. Dit is bewys in plante wat in PS grond gegroei het waar 93.3% plante oorleef het waar die grondoppervlakte bedek was teenoor 60% oorlewendes waar die grondoppervlakte nie bedek was nie indien glifosaat teen 1/8x toegedien is. ‘n Soortgelyke tendens is by die 1/4x dosis waargeneem. ‘n Teenoorgestelde effek is in SS grond waargeneem waar die oorlewingspersentasie in bedekte en onbedekte grond by 1/4x glifosaatdosis 0% en 40% onderskeidelik was. Glifosaat is aanvanklik aangeprys as ‘n omgewingsvriendelike onkruiddoder omdat dit vinnig in grond afgebreek word en omdat dit geadsorbeer word aan metale in die grondmatriks. In teenstelling hiermee is daar egter verslae in die literatuur wat dui daarop dat glifosaatresidue in die grond gewasopbrengste kan verlaag. In die gemelde studies is gevind dat fitotoksisiteit van glifosaat residue afhang van grondeienskappe en grondvrugbaarheid. Na aanleiding hiervan is ‘n glashuisstudie uitgevoer waarin die fitotoksisiteit van residuele glifosaat op ‘n kommersiële raaigraskultivar wat in PS, CS en SS gronde groei, ondersoek is. Glifosaat is op die grond in potte toegedien teen 0 (G1), 540 (G2) and 3240 (G3) g a.b. ha-1. Raaigras saailinge is daarna in die potte ingeplant twee ure, drie weke en vier weke nadat die glifosaat toegedien is. Bewys van grondaktiwiteit van glifosaat is gelewer deur die vermindering in persentasie oorlewing van die saailinge met toediening van glifosaat. Die vermindering in oorlewing was betekenisvol in die SS grond waar ongeveer 60% en 48% oorlewing van saailinge was by G2 en G3 dosisse onderskeidelik teenoor 100% oorlewing in die onbehandelde kontrole. Die afname in persentasie oorlewing is deur tyd beïnvloed deurdat die G2 dosis slegs by die twee ure behandeling betekenisvolle verlaging in oorlewing veroorsaak het terwyl die G3 dosis by die twee ure sowel as die drie weke behandeling betekenisvolle verlagings veroorsaak het. Vier weke na toediening was daar geen effek van glifosaat op die saailinge in enige van die gronde gewees nie. Soortgelyke tendense is waargeneem by die droëmassa en lengte data. Spoorelemente wat noodsaaklik is vir normale plantgroeiprosesse is al geïmpliseer in verlaging van glifosaat effektiwiteit. Dit is waarskynlik omdat glifosaat oorspronklik ontwikkel is as ‘n metaal cheleerder. Glifosaat-spoorelement antagonisme was onlangs in die nuus nadat glifosaat saam met sulke elemente toegedien is op glifosaat weerstandbiedende sojabone. Molibdeen (Mo), ’n anioon, mag ’n rol op fisiologiese vlak speel in doie effektiwiteit van glifosaat. ‘n Glashuisstudie is uitgevoer waarin saailinge van ‘n glifosaat vatbare kommersiële raaigras kultivar en ‘n glifosaat weerstandbiedende raaigras biotipe besproei is met voedingsmengsels wat 0x, 1x en 2x Mo bevat waar 1x 0.05 mg L-1 Mo is. Glifosaat is op die plante toegedien teen 0 (0x), 135 (1/4x), 270 (1/2x), 540 (1x) and 1040 (2x) g a.b. ha-1 dosisse. Die 2x Mo toediening het gelei tot 0% oorlewing in die R biotipe by 1x GAR vergeleke met 50% en 90% oorlewing by dieselfde GAR met 0x en 1x Mo. In terme van droëmateriaal en lengtegroei was daar geen konkrete tendense nie.

Thesis (MScAgric (Agronomy)--Stellenbosch University, 2008. / Honeybush (Cyclopia spp. Fabaceae) is indigenous to the fynbos botanical biome of the Eastern and Western Cape of South Africa. The increase in the international demand for honeybush tea for health benefits, concern over exploitation of wild populations and the lack of published agronomic information necessitated this study to evaluate different aspects of honeybush propagation. The main objectives of this study were to evaluate the effect of species and cutting position on rooting of cuttings of Cyclopia species using different rooting hormones, to evaluate the effect of an organic plant fertilizer and cutting position on growth and establishment of rooted cuttings and to study the influence of different seed pre-treatments on germination of Cyclopia species. Terminal and sub-terminal cuttings of C. intermedia and C. genistoides treated with different rooting hormones were rooted under day/night temperature controlled glasshouse conditions. Intermittent mist was used as means of moisture supply to the cuttings for 45-60 seconds daily every 30 minutes. C. genistoides rooted significantly better compared to C. intermedia as measured by rooting percentage, number of roots per cutting, length of longest root and mean root length during the summer season. The cutting position had a significant effect on rooting of the cuttings in summer compared to winter and spring season. The interactive effect of species, treatment and cutting position resulted into 86% of rooting in summer from the terminal cuttings of C. genistoides, while only 4% was recorded as the highest rooting percentage in both winter and spring seasons. The highest number of roots and the greatest root length per cutting were obtained with 2 and 4 g L-1 IBA from terminal cuttings of C. genistoides and these hormone concentrations were not significantly different to each other. To evaluate the effect of an organic plant fertilizer and cutting position on plant growth and establishment, rooted cuttings of two Cyclopia species (C. intermedia and C. genistoides) from two cutting positions (terminal and sub-terminal) were transferred to pots (576 cm3) and treated with Nitrosol fertilizer at application rates of 3.33 ml.L-1, 1.67 ml.L-1 and 0 ml.L-1 (control). Cyclopia plantlets were uniformly inoculated once with a symbiotic Rhizobium bacteria to improve the formation of nodules. Nitrosol® at 3.33 ml.L-1 significantly affected fresh and dry plant weight, fresh and dry root weight, number of shoots and nodules per plant compared to either 1.67 ml.L-1 or the control. Relative to species, C. genistoides performed better in terms of fresh and dry plant weight, fresh and dry root weight, and number of shoots and nodules per plant compared to C. intermedia. The origin of the cutting position did not significantly affect the above mentioned parameters. Plant mineral analysis revealed that most of the essential elements increased with increasing Nitrosol® application rates, with C. genistoides having higher levels of mineral elements than C. intermedia. This could be an indication of the differences between the two species in terms of nutrient uptake, utilization and distribution within the plant tissues. In the germination studies, seeds obtained from different seed sources of Cyclopia species were subjected to different pre-sowing treatments. Seed treatments were sulphuric acid (95%), hot water (100°C), water with smoke paper disk, and demineralised water (control). The study revealed that all the treatments had a significant effect on germination with the exception of eight year old seeds obtained from C. subternata (seed source two). Although hot water treatment improved germination compared to smoked paper disk and the control, seeds treated with hot water degenerated rapidly. The highest overall germination (77.33%) was found with one year old seeds compared to other seed sources older than one year. Although smoked paper disks generally did not improve germination compared to the control, in one year old seeds from seed source one, this treatment greatly influenced germination, suggesting that seed age might have influenced germination of these seeds. In terms of germination rate, germination generally started after four days in most treatments.

Thesis (MScAgric)--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: Potatoes is the fourth most important food source in the world. To provide in the ever increasing demand by the growing world population for this staple food, alternative ways will have to be found to produce a cheaper and a healthier end product. The tubers mainly consist of carbohydrates and starch, although 9% of the dry weight of the tubers consist of proteins. In its natural state the potato tuber is low in sodium and high in potassium and vitamin C. These proteins can provide in all the amino-acid requirements of humans and make it an outstanding balanced diet. The most important factor by which the production and quality of potatoes can be increased, is to provide better propagation material to producers. Minituber production is a relatively new method of producing better quality propagation material for producers. It is, however, very expensive because of the high capital investment needed. By producing more tubers per plant, or more tubers per square meter, the unit price per tuber may be lowered. The system commonly used for minituber production is where in vitro plants are planted in a greenhouse, usually in a vermiculite/peat mixture as medium. As in a hydroponic system, nutrients are added to the irrigation water. As possible strategy to increase the production of mini-tubers, the effect of nutrition was investigated. No significant differences were found in tuber production with small deviations in phosphorous and calcium nutrition. Researchers who reported significant differences in tuber production with nutrition, either corrected extreme shortages or induced it. By subjecting the root and tuber medium of potato plants to a pH-shock (nutrient solution with a pH of 3.5 for 10 hours), large amounts of tubers were initiated. A new production technique was developed where plants were grown in a hydroponic way without any root medium. In this way the right sized tubers could be removed without damaging the plant. Potato plants do not initiate tubers easily where stolons are not subjected to mechanical resistance. This problem was solved with the help of a pHshock, where significantly more tubers were formed per plant. The action of the pH-shock could be explained by a temporary inaccessibility of nutrients to the plant. Both calcium and magnesium absorpsion are hampered at a low pH, but calcium is also poorly translocated in the plant. Considering that a nutrient solution without calcium produced the same results as the pH-shock treatment in this study, one may make the assumption that an induced calcium shortage may be responsible for the low pH effect. The same effect may even be induced by giving the plants clean water for some time. Such a treatment was, however, not tested but should receive attention in further studies. The correct timing for a low pH-shock may need more research. A precise number of days after transplanting can not be prescribed since many factors such as light intensity, daylength and cultivar difference affect plant growth and tuber initiation. Environmental conditions, the physiological age and the biomass of the plant may affect the timing of the shock. A low pH-shock could not at any stage induce tubers in potato plants where unfavorable environmental conditions occurred. It seems as if the plants need to be ready for tuber initiation before the pH-shock can be successfully applied. By removing/harvesting the tubers at the required weight, the burden on the plant may be relieved enabling more tubers to form. It was experienced that the reproductive system of the potato plant is complex with a number of factors affecting it. The new production system has potential, but more developmental work is still needed. / AFRIKAANSE OPSOMMING: Aartappels is die vierde belangrikste voedelsoort in die wereld, Om te kan voorsien aan die ewigdurende verhoogde vraag na hierdie stapelvoedel deur die groeiende wereld-bevolking, sal daar maniere gevind moet word om die eindproduk goedkoper en in 'n gesonder toestand op die mark te plaas. Die knolle bestaan hoofsaaklik uit koolhidrate en stysel, alhoewel 9% van die droe gewig van knolle uit proteiene bestaan. Die aartappelknol is in sy natuurlike toestand laag in natrium en hoog in kalium en vitamien C. Hierdie protei'ene kan in al die aminosuur-behoeftes van mense voorsien wat dit dus 'n uitstekende gebalanseerde dieet maak. Die belangrikste faktor waarmee die produksie en kwaliteit van aartappels verhoog kan word is om beter voortplantingsmateriaal aan produsente te verskaf. Miniknolproduksie is 'n relatief nuwe manier om gesonde en groeikragtige voortplantingsmateriaal vinnig by die produsente te kry. Dit is egter 'n duur metode omdat die kapitaal-investering groot is. Deur meer knoUe per plant, of meer knolle per vierkante meter te produseer kan die eenheidsprys per moer verlaag word. Die sisteem wat algemeen vir miniknolproduksie gebruik word is om in vitro plantjies in 'n kweekhuis, gewoonlik in 'n vermikulietldennebas mengsel te plant. Voedingstowwe word dan soos in 'n hidrokultuurstelsel saam met die besproeiingswater toegedien. As moontlike strategie om die produksie van miniknolle by aartappels te verhoog, is die invloed van voeding daarop ondersoek. Daar is gevind dat daar nie groot verskille in knolproduksie met klein afwykings in fosfaat- en kalsium-voeding veroorsaak is nie. Navorsers wat wel betekenisvolle verskille III knolproduksie met voedingsbehandelings verkry het, het ekstreme tekorte reggestel of gemduseer. Deur die wortel- en knolmedium van aartappelplante aan 'n pH-skok (voedingsoplossing met 'n pH van 3.5 vir 10 ure) bloot te stel, is daar gevind dat 'n groot hoeveelheid knolle geinisieer word. Verder is 'n nuwe produksietegniek ontwikkel waar die plante met 'n suiwer waterkultuur metode geproduseer word, sodat knolle wat oesgereed is verwyder kan word. Aartappelplante inisieer nie maklik knolle onder hierdie omstandighede waar stolons geen meganiese weerstand ervaar nie. Met behulp van die pH-skok het daar betekenisvol meer knolle per plant gevorm. Die werking van die pH-skok kan moontlik aan 'n tydelike ontoeganklikheid van voedingstowwe toegeskryf word. Beide kalsium en magnesium word moeilik by 'n lae pH opgeneem maar kalsium word boonop moeilik deur die plant getranslokeer. Aangesien 'n voedingsoplossing sonder enige kalsium dieselfde resultate as die pHskok gelewer het, lyk dit asof 'n geinduseerde kalsium-gebrek vir die lae pH effek verantwoordelik mag wees. Die skok kan makliker en veiliger toegepas word deur vir 'n tydperk net skoon water aan die plante te gee. So 'n behandeling is egter nie beproef nie maar behoort in opvolgwerk aandag te ontvang. Die optimum tyd waarop so 'n skok toegedien moet word is nog onduidelik. Daar kan nie op 'n eksakte aantal dae na uitplant gewerk word nie, aangesien daar te veel faktore soos ligintensieteit, daglengte en kultivar is wat plante se groei en knolinisiasie kan beinvloed, Omgewingstoestande, die fisiologiese ouderdom van die plant en die hoeveelheid biomassa wat gevorm het mag bepaal wanneer die plante geskok moet word. Waar ongunstige omgewingstoestande geheers het, kon 'n lae-pHskok op geen stadium knolinisiasie induseer nie. Dit wil voorkom asof die plant vir 'n knolinisiasie fase gereed moet wees voordat 'n lae-pH-skok doeltreffend is. Dit verhoog dan bloot die aantal knolle wat per plant ontwikkel. Deur die knolle op die verlangde grootte te pluk kan die las op die plante verlig word sodat meer knolle mag vorm. Daar is ervaar dat die reproduktiewe stelsel van die aartappelplant kompleks is en dat daar baie faktore is wat dit mag beinvloed. Die nuwe produksiestelsel toon potensiaal, alhoewel verdere ontwikkelingswerk nog nodig is.

Thesis (MScAgric (Agronomy))--Stellenbosch University, 2008. / The development of herbicide resistance in weeds is one of the major factors hampering profitable crop production worldwide. In South Africa resistance to herbicides in weeds is also a big problem, in particular in the Winter Rainfall Region of the country. The lack of sufficient different mode of action herbicide groups that can be rotated in these conditions necessitate the implementation of integrated weed management programmes to curb the development and spread of herbicide resistance. One of the alternative physical weed management strategies is to maximize crop competition to the weed population. One aspect of such a strategy is to plant crop cultivars that have greater interference potential than others.

Thesis (MScAgric)--University of Stellenbosch, 2005. / ENGLISH ABSTRACT: Ripgut brome (Bromus diandrus Roth.) is a weed that causes great problems in the most wheat and grain producing areas and also in livestock practices. Until recently (1995) there were no registered chemicals for the management of ripgut brome in wheat, in South Africa. After the registration of sulfosulfuron and iodosulfuron + mesosulfuron for the management of ripgut brome in wheat, these two herbicides were widely used and in the case of wheat monocultures, it was used repeatedly. During the last few years, reports of ripgut brome that were suspected to be resistant to these chemicals, increased. With the development of herbicide resistance it is of great importance to investigate methods to confirm resistance and also to control it. The goal of this study was firstly, to confirm resistance in ripgut brome and secondly to compare growth and development of resistant ripgut brome popualtions to that of susceptible ripgut brome populations. The dormancy of Bromus seed was also investigated as were effective methods to break seed dormancy. Lastly, quicker methods to confirm resistance were investigated. A short summary of the experiments follows. In the first experiment the degree of resistance of three different ripgut brome populations were determined, by using the pot spray method. One population each of B. pectinatus and B. rigidus were also included in the study. The seed of the Bromus populations were germinated after which it was planted in plastic pots and were placed in the glasshouse until the three to four leaf stage. Subsequently the plants were treated with the following four herbicides: sulfosulfuron, iodosulfuron + mesosulfuron, imazamox and haloxyfop-R methyl ester, at seven concentrations namely, the recommended dosage, one quarter, one half, twice, four times and eight times the recommended dosage. After six weeks the percentage survival and the dry mass of the plants were determined. Results showed that the three ripgut brome populations had different degrees of resistance to sulfosulfuron and iodosulfuron + mesosulfuron, varying from no resistance to moderate resistance to strong resistance. There was no resistance to imazamox and haloxyfop-R methyl ester. The B. rigidus population exhibited strong resistance or tolerance (natural resistance) to the two sulfonylureum herbicides. In the second experiment the seed of the same Bromus populations were germinated and planted in plastic pots that were filled with three litres of river sand to determine the growth, development and seed production of the plants. The number of leaves for each plant as well as the plant height were measured weekly, until the plants became reproductive. The two resistant populations grew much faster than the susceptible population and they also produced taller plants. The susceptible population produced more leaves, but seed production was delayed considerably. This probably relates more to the plant’s adaptation to their enviroment, than to adaptation due to resistance. The susceptible population was collected from a natural environment, while the others were collected from wheat fields. In the third experiment the seed dormancy of the Bromus populations was investigated. The effect of different treatments on the dormancy of the seed was also investigated. The treatments that were applied were gibberrellic acid, fumigation with ammonia gas and an ammonia treatment combined with a cold treatment. Seed dormancy in all populations was short-lived and the cold treatment was an effective way of stimulating fresh seed to germinate. The last experiment was performed to develop a quicker method for the evaluation of resistance in Bromus spp. In this experiment the petridish method was investigated. Only sulfosulfuron and iodosulfuron + mesosulfuron were used, because resistance to them was proven earlier. Different concentrations of the herbicides were applied to the dishes with the seed and were exposed to a cold treatment before being placed in a germination chamber. The seed in al the treatments germinated and it was decided to let the seed grow for two weeks in the petri dishes to observe whether the herbicides may have a detrimental effect on the growth of the small seedlings. After two weeks there were no differences between treatments and the experiment was terminated. The study showed that resistance is present in some of the Bromus populations and that there are biological differences between populations with different degrees of resistance. However, the fact that the susceptible population comes from a completely different environment than the other populations, complicate matters and further studies are required to obtain a clearer picture. / AFRIKAANSE OPSOMMING: Predikantsluis (Bromus diandrus Roth.) is ‘n onkruid wat in die meeste koringen garsproduserende gebiede, asook in sommige vee praktyke, probleme veroorsaak. Tot redelik onlangs (ongeveer 1995) was daar in Suid-Afrika geen middels geregistreer wat predikantsluis in koring kon beheer nie. Nadat sulfosulfuron en iodosulfuron + mesosulfuron vir predikantsluisbeheer in koring geregistreer is, is die twee middels op groot skaal, en in die geval van koring monokultuurstelsels, aanhoudend toegedien. Gedurende die afgelope paar jaar is berigte ontvang dat beheer van predikantsluis met die middels nie meer so doeltreffend is nie, moontlik as gevolg van onkruiddoderweerstand wat ontwikkel het. Met die ontstaan van onkruiddoderweerstand is dit belangrik om praktyke en maniere te vind om weerstand vinniger te bevestig en doeltreffend te bestuur. Die doel van hierdie studie was eerstens om weerstand in predikantsluis te bevestig en tweedens om die groei en ontwikkeling van plante afkomstig van vermoedelike weerstandbiedende predikantsluis populasies te vergelyk met plante uit ‘n vatbare populasie. Die saadproduksie en dormansie van die saad is ook ondersoek asook effektiewe metodes om dormansie te breek. Laastens is ondersoek ingestel na ‘n vinniger manier (petribakkie metode) om weerstand te bevestig. Hieronder volg ‘n oorsig oor die vier eksperimente wat uitgevoer is. In die eerste proef is die mate van weerstand van drie verskillende predikantsluis populasies bepaal, deur van die gewone potspuit metode gebruik te maak. Daar is ook een populasie elk van Bromus pectinatus en vermoedelik Bromus rigidus ingesluit in die studie. Die sade van die verskillende populasies is toegelaat om te ontkiem en daarna is dit in plastiese potjies geplant en in ‘n glashuis geplaas totdat die drie tot vier blaarstadium bereik is. Die plante is daarna gespuit met die volgende vier middels: haloksifop-R-metielester (Gallant Super), imasamoks (Cysure), iodosulfuron + mesosulfuron (Cossack) en sulfosulfuron (Monitor), teen sewe konsentrasies elk, nl. teen die aanbevole dosis, asook teen een kwart van, een helfte van, twee keer, vier keer en agt keer die aanbevole dosis. Na ses weke is die persentasie oorlewendes en die droëmassa van die plante bepaal. Resultate het getoon dat die drie predikantsluis populasies verskillende grade van weerstand teen die twee sulfonielureums (sulfosulfuron en iodosulfuron + mesosulfuron) toon, dit wil sê van geen tot matig tot sterk weerstandbiedend. Daar is egter geen weerstand teen haloksifop-R-metielester (Gallant Super) en imasamoks (Cysure) waargeneem nie. Die B. rigidus populasie het sterk weerstand of toleransie (natuurlike weerstand) teen die sulfonielureum middels getoon. In die tweede proef is saad van dieselfde Bromus populasies ontkiem en oorgeplant in plastiese potte gevul met 3 liter riviersand om die groei en ontwikkeling en saadproduksie van die plante te evalueer. Die aantal blare per plant en hoogte van die plante is weekliks bepaal totdat die plante reproduktief geraak het. Hierna is die metings gestaak om te voorkom dat die saadproduksie van die plante benadeel word. Die resultate het getoon dat die twee weerstandbiedende predikantsluis populasies vinniger groei as die vatbare populasie en ook langer plante vorm, terwyl die vatbare populasie vinniger en meer blare vorm, maar langer neem om saad te vorm. Hierdie waarnemings hou egter waarskynlik meer verband met die oorsprong van die populasies as met die graad van weerstandbiedendheid. Die vatbare populasie is versamel in natuurlike veld vêr van enige landerye terwyl die ander populasies almal uit graanlande afkomstig is. In die derde proef is saaddormansie van die Bromus populasies ondersoek. Daar is ook ondersoek ingestel na verskillende behandelings om dormansie te breek. Die behandelings wat toegepas is, is ‘n gibberelienesuur behandeling teen verskillende konsentrasies, beroking met ammoniak vir verskillende tye en ‘n ammoniak behandeling tesame met ‘n koue behandeling. Die resultate het getoon dat saaddormansie van die Bromus populasies van korte duur is, maar dat kouebehandeling effektief is om ontkieming van vars saad te stimuleer. Die vierde proef is uitgevoer om vas te stel of daar vinniger evaluasiemetodes is vir die evaluasie van weerstand in Bromus spp., deur van die petribakkie metode gebruik te maak. In hierdie proef is slegs die middels iodosulfuron + mesosulfuron (Cossack) en sulfosulfuron (Monitor) gebruik, omdat daar ‘n mate van weerstand teen hulle waargeneem is in die eerste proef. Die middels is teen verskillende konsentrasies in petribakkies gevoeg, tesame met die sade en toe blootgestel aan ‘n kouebehandeling voordat dit in ‘n ontkiemingskabinet geplaas is vir ontkieming. Die sade in al die behandelings het ontkiem en daar is besluit om die saailinge uit die ontkiemingskabinet te haal en vir twee weke te laat groei sodat daar bepaal kon word of die middels ‘n effek op die groei van die plantjies het. Na twee weke kon geen verskil in die groei van die plantjies waargeneem word nie en die proef is beëindig. Die studie het getoon dat daar wel weerstand in sommige van die Bromus populasies voorkom, en dat biologiese verskille voorkom tussen predikantsluis populasies met verskillende grade van weerstand. Die feit dat die vatbare populasie uit ‘n heeltemaal verskillende omgewing kom as die ander populasies, maak definitiewe afleidings moeilik. Daar sal opvolgstudies uitgevoer moet word om van die onduidelikhede op te klaar.

Thesis (MScAgric)--Stellenbosch University, 2011. / 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. / AFRIKAANSE OPSOMMING: Die potensiële belang van grondlose produksietegnieke, veral by tamaties, in Suid-Afrika wat toenemend meer water skaars raak, motiveer dat navorsing onder plaaslike toestande gedoen moet word. By grondlose produksie stelsels word die toediening en die beskikbaarheid van voedingstowwe nou gekoppel aan dié van water. Navorsing rakende metodes wat water en kunsmis gebruiks doeltreffendheid sal verhoog en terselfdertyd besoedeling van die omgewing voorkom asook die opbrengste en kwaliteit van tamaties behou of verbeter is dus van uiterste belang. Swak bestuur van bemesting in hidroponiese stelsels gee aanleiding tot water besoedeling en vermorsing van kosbare water en duur kunsmis. Snoei is 'n belangrike kulturele praktyk om hoë produktiwiteit by hidroponiese tamaties te verseker. Die aanpassing van snoei praktyke by klimaatstoestande is 'n goedkoop en doeltreffende manier om produktiwiteit te verbeter sonder om insette te verhoog. Die verbetering van water en kunsmis gebruiks doeltreffendheid is dus noodsaaklik om te verseker dat intensiewe gewasse, soos tamaties, volhoubaar geproduseer word. Drie eksperimente is uitgevoer om die effek van snoei en bemesting op die groei, opbrengs en water en kunsmis gebruiks doeltreffendheid van hidroponiese tamaties te ondersoek. In die eerste eksperiment is die effek van die EG, besproeiings frekwensie en groeimedium op die water gebruik, voedingstofopname, opbrengs en kwaliteit van tamaties ondersoek. 'n Faktoriaal ontwerp met gesplete plotte is gebruik. Twee EG behandelings (1 en 2 mS.cm-1), 3 besproeiings behandelings (5x, 10x, 20x per dag) en 3 groei media (kokos, sand, saagsels) is ondersoek. Selfs by ‘n EG van 1 mS.cm-1 was die voedingstof opname van plante vergelykbaar met waardes wat geassosieer word met blaar ‘n voedingstof inhoud wat voorgeskryf vir optimale produksie. die verhoging van die absolute voedingstof konsentrasie het ook 'n klein uitwerking op voedingstofopname gehad. In die organiese media - kokos en saagsels – het die beskikbare N vroeg in die seisoen verminder, en die tamaties wat in kokos gegroei het, het ook ‘n verminderde Ca opname getoon in vergelyking met die plante wat in sand en saagsels gegroei het. Die plate wat in kokos gegroei het, het meer water gebruik in vergelyking met plante wat in sand en saagsels gegroei het. Plante besproei met ‘n voedingsoplossing van 1 mS.cm-1 EG het minder water gebruik as die plante wat besproei met ‘n voedingsolossing by ‘n EG van 2 mS.cm-1. Tamaties wat gekweek word by 'n EG van 1 mS.cm-1 het nie beduidend verskil van hoër EG plante in terme van bemarkbare en groen vrugte nie. Plante wat gekweek is by die laer EG het ‘n aansienlike laer persentasie oplosbare vastestof inhoud (Brix) in vergelyking met die hoër EG-behandeling gehad. Die tweede eksperiment het die effek van blaar- en vrug snoei op die vruggrootte, totale opbrengs en bemarkbare opbrengs van tamaties ondersoek. Plante is vertikaal opgelei tot by die horisontale draad en na twee stamme gesnoei. Drie verskillende blaar snoei behandelings is toegepas: geen blaar snoei, snoei elke 2de jong blaar na 1m plant hoogte en snoei van elke 2de jong blaar na 2m plant hoogte. Twee vrug snoei behandelings is ook toegepas: geen vrugte gesnoei en trosse gesnoei tot 4 vrugte. ‘n Faktoriale ontwerp is vir hierdie eksperiment gebruik. Blaar snoei behandelings het geen effek gehad nie, waarskynlik omdat die jong blare te laat verwyder was. Met die vrug snoei behandelings was daar geen beduidende verskil tussen die behandelings in terme van bemarkbare opbrengs nie. Plante waarvan die trosse nie gesnoei was nie het 'n aansienlik hoër totale opbrengs gelewer, asook ‘n hoër vroeë opbrengs maar ‘n laer gemiddelde bemarkbare vrug massa en ‘n hoër persentasie onbemarkbare vrugte (baie klein vrugte in vergelyking met die gesnoeide behandeling). Vanuit hierdie resultate kan daar afgelei word dat vrug snoei nie nodig is tydens ‘n kort groeiperiode vir tamaties nie, alhoewel dit wel ‘n rol mag speel gedurende ‘n langer groeiperiode. Met die derde eksperiment is die gekombineerde effek van verskillende EG en stam snoei praktyke op voeding, groei en vroeë opbrengs van hidroponies verboude tamaties bepaal. 'n faktoriale ontwerp is gebruik, met twee EG behandelings (1 en 2 mS.cm-1) en 2 stam snoei behandelings (enkel en dubbel). Stam snoei het ‘n geringe uitwerking op die groei van die plant gehad, maar het wel die ontwikkeling van plante verander. Plante gesnoei na twee stamme het aansienlik meer trosse gehad, maar nie 'n hoër DM of blaar oppervlak as die enkele stam plante nie. Stam snoei se grootste effek blyk te wees op die aantal vrugte per plant en dit kan op die lang termyn lei tot verskille in die groei van plante en hul voeding. EG 1 mS.cm-1 plante het ‘n aansienlik laer blaaroppervlakte en droë massas geproduseer, maar het 'n aansienlik hoër bemarkbare opbrengs in vergelyking met EG 2 mS.cm-1 plante gelewer. Oorbemesting kan 'n negatiewe impak op die vroeë opbrengste van tamaties hê, terwyl laer bemesting in die vroeë stadiums van groei vroeë opbrengs bevoordeel maar blaaroppervlak ontwikkeling beperk wat dan ook produktiwiteit beperk in die lang termyn. Hierdie verskille in groei word hoofsaaklik toegeskryf aan verskille in die N-en P-voeding.

Thesis (MScAgric (Agronomy)--University of Stellenbosch, 1999. / The Western Cape is one of the most important onion producing regions in South Africa. It is well suited for the production of intermediate daylength onion cultivars. Annually about 2500 ha are planted with a yield of about 120 000 tons. Only 9 000 tons was exported in 1998 and of these 9 000 tons 4.9% was rejected due to poor quality. In South Africa there are no guidelines for the production of intermediate daylength onions. It is very important to have fertiliser guidelines, because optimal yields of good quality can be achieved with a good fertiliser program. Produce with exceptional quality can boost exports and at the same time stabilize local markets. However fertilisers are very expensive and could be damaging to the environment ifused incorrectly. To produce fertiliser guidelines N, P and K field trials were planted at three differen~ localities (Koue Bokkeveld, Stellenbosch and Caledon). The localities were chosen according to the difference in climate and soil texture, and these are important onion growing areas. The minimum and maximum temperature for the Koue Bokkeveld, Stellenbosch and Caledon was 11123, 12/25 and 13/27 °C respectively. At all the localities 3 nitrogen-, 4 phosphorus- and 4 potassium levels were used. Treatments were factorially arranged in a randomised block design, with two replicates. At Stellenbosch a N fertiliser trial was planted with four N levels and four N application methods. The treatments were factorially arranged in a completely randomised block design, with three replicates. N, P and K was applied as limestone ammonium nitrate, single superphosphate and potassium sulphate. Marketable and unmarketable bulbs were quantified at harvest. Weight loss during storage was determined over a six month period and storage disorders were evaluated. It was clear that high N levels, especially on soil with a high potential for releasing N, had a negative effect on yield and keeping quality. At Caledon a significant reduction in yield took place with the highest N level. High N levels also had a significant effect on weight loss at Stellenbosch and Caledon. The same trend with high N levels occurred in the N fertiliser trial. Weight loss was increased with the late application ofN in the growing season. In spite of the fact that the P levels were high (58 - 66 mg.kg-I) in the different soils, the onions reacted very well to phosphorus fertiliser. As a result of the higher P levels there was more foliage in the leaf canopy and the bulbs were larger. This P reaction only occurred in the Koue Bokkeveld and at Caledon. At Stellenbosch yield was not improved with P fertilisation and bulbs were of poor quality. The highest P level resulted in the greatest weight loss in storage. K had an effect where the K status and clay content of the soil was low. High potassium levels improved yield and keeping quality remarkably in the Koue Bokkeveld. Some interactions also occurred. The percentage unmarketable bulbs were influenced by a P and K interaction. An increase in double bulbs was responsible for the increase in the percentage unmarketable bulbs. At the lowest P level, higher K levels decreased the percentage unmarketable bulbs. Alarming proportions were reached when high K levels were combined with the highest P level. The P and K interaction also had an effect on the percentage sprouting. K did not have any effect' on sprouting at low P levels. A combination of the highest P level and the lowest K level produced the highest percentage sprouting. The interaction between N and P, like the P and K interaction had an effect on the percentage sprouting. The highest N level in combination with the highest P level increased the percentage sprouting significantly. The N, P and K field trials showed that the optimum N level is less than 130 kg N.ha-l on a soil with 16 % clay. On a sandy soil it can be as high as 160 kg N.ha•l The optimum P level varied from 30 to 130 kg P.ha-l Where a poor P reaction was observed the Ca and S status in the soil was low. It is possible that the drastic P reaction with superphosphate (10.5 % P, 20.3 % Ca, 12.1 % S) in the Koue Bokkeveld can be a result of the application of Ca and S. On the shale soil at Caledon, with a K status of 288 mg.kg-\ the optimum K level is less than 75 kg K.ha-l On the sandy soil of the Koue Bokkeveld, with a K status of 43 mg.kg•l , the optimum K level was 200 kg K.ha•l . The N fertilisation trial was done on a soil with an optimum N level of 115 kg N.ha-l (10 % clay). It was demonstrated that the standard N application method (40 % N with planting and the rest divided in three equal applications of 20 % N on 2, 4 and 7 weeks after planting) is still an acceptable practice. Follow-up trials are being done to determine the exact optimum level of fertilisation.

Thesis (MScAgric (Agronomy)--University of Stellenbosch, 2007. / An increase in the demand of buchu (Agathosma betulina) oil has lead to an increase in the commercial cultivation of buchu in fields and also in hydroponic systems. A nutrient solution for hydroponically grown buchu is still required to ensure optimal growth and yield. ASNAPP (Agribusiness in Sustainable Natural African Plant Products) South Africa has done some trials to achieve optimal EC and pH in the nutrient solution. Phosphate concentrations in the nutrient solution might play a significant role due to reports by a variety of researchers on the sensitivity of Protea plants to phosphate. Buchu and Proteas are both part of the Fynbos biome and are found in regions with similar soil (sandy soils with a low pH and mineral contents) and climatic conditions. Two separate experiments were conducted to determine the effect of increasing phosphate concentrations (ranging from 0.00 to 1.40 me L-1) in the nutrient solution on buchu growth. The first experiment was done in a plastic covered structure with a pad and fan and the objective of this trial was to determine the effect of increasing phosphate concentrations in the nutrient solution on the general growth, biomass production, oil composition, mortality rate and chemical composition of the buchu plants. The second experiment was done in a glasshouse with mechanical temperature control and the aim of this trial was to determine the response of buchu to increasing concentrations of P at two different root temperatures. A chemical analysis of the plants was done and the general growth, yield and root mass were recorded to determine the response of buchu plants to the phosphate and temperature treatments. In the greenhouse experiment an optimum growth and yield response of buchu plants was found at a phosphate concentration of 0.7 me L-1 in the nutrient solution. Phosphate concentrations lower or higher than 0.7 me L-1 lead to a decrease in growth and yield. An increase in the phosphate concentration in the nutrient solution lead to a general increase in N, P, K, Ca, Mg and B content in the buchu plants and a decrease in Fe content. The mortality rate of the buchu plants increased with an increase in the phosphate concentration from 0.0 to 1.4 me L-1 in the nutrient solution. The phosphate concentration in the nutrient solution only made a significant difference on one major component of the buchu oil which was Ψ-Diosphenol, but no general trend with Ψ-Diosphenol content and P concentration could be found and the significant difference in Ψ-Diosphenol observed in this trial may only have been due to genetic variation between the plants. The effect of the different root temperatures in the glasshouse experiment was very clear. The buchu plants grown at the high root temperature (20°C) produced a higher yield and better overall growth than the plants grown at lower (10°C) temperatures. The buchu plants grown at 20°C had a significantly higher N, K, Na and B content than plants grown at 10°C. Buchu plants grown at 10°C showed no significant response in terms of growth and yield to the phosphate concentration in the nutrient solution, but plants grown at 20°C exhibited growth and yield peaks at phosphate concentrations of 0.35 and 1.4 me L-1. The peak observed in the plants growth at high phosphate concentrations is unexplainable and can possibly be ascribed to the limitation of the plants per experimental unit and/or amount of replications. The increase in P concentration in the nutrient solution caused a general increase in N, P and K content in the buchu plants. A significant interaction between the phosphate concentration and root temperature was observed for the P, Mn en Zn contents of the plants which meant that the buchu plants respond differently towards phosphate concentrations at different root temperatures.

Thesis (MScAgric (Agronomy))--Stellenbosch University, 2008. / The use of hydroponic strawberry production systems is increasing worldwide. Although higher planting densities are possible in vertical production systems, these higher planting densities may have a negative effect on individual plant yield and fruit quality due to lower light levels when compared to conventional (horizontal) production systems. Optimum planting densities will for this reason be affected by light intensities inside the greenhouse and configuration of the vertical production systems. Two experiments were conducted in a plastic cladded greenhouse, fitted with a wetwall and fan cooling system, at the Department of Agronomy, University of Stellenbosch, South Africa during the period of April 2007 to November 2007 (late autumn to early summer). Mean daily maximum temperatures exceeded 26 oC during most of the 14 week harvest period (22 August to 30 November 2007), while photosynthetic active radiation (PAR), measured at 12h00 on cloudless days, inside the greenhouse increased from about 200 μMol m-2 s-1 to about 460 μMol m-2 s-1 during this period. The first experiment compared the effect of two vertical production systems (vertical system and ‘A-shape’ system), subjected to different planting density (16.7, 23.3 and 33.3 plants m-2) and shading (0%, 20%, 50%) treatments, as measured on selected yield, quality and growth factors. The second experiment studied the effect of different planting density (3.3, 5.6 and 10 plants m-2) and shading (0%, 20%, 50%) treatments on the same yield, quality and growth factors in a conventional production system. A comparison with regard to these factors was also made between the highest planting densities of the conventional-, vertical- and ‘A-shape’ system.

University of Stellenbosch. Faculty of Agrisciences. Dept. of Agronomy. / Thesis (MScAgric (Agronomy)--University of Stellenbosch, 2007. / Calcium (Ca) is an important plant nutrient with many functions, such as strengthening of cell walls and maintaining membrane stability and cell integrity. A greenhouse experiment was conducted using an aeroponic production system, to evaluate the influence of different Ca: K & Mg ratios (consisting of a control [100% Ca], and three treatments in which the Ca levels were changed to 33%, 66% and 133% of the control, while the K and Mg levels were adjusted to compensate for the change in Ca) and two different irrigation methods (irrigation on roots only, and irrigation on roots and stolons) on tuber yield and mineral concentration. The treatment that received the highest Ca: K & Mg ratio had significantly more larger tubers than the lowest Ca treatment, although there was no significant difference in total tuber number between treatments. The high Ca treatment also had a significantly higher Ca concentration in the skin than the low Ca treatment. The site of irrigation did not have a significant effect on the total tuber number per plant, or on the Ca content of the tubers that were produced. The tubers produced in the first experiment were divided into two weight classes, and stored at three different temperatures. The percentage weight loss during storage was determined by weighing the tubers before, and again after storage. The firmness of the tubers was also measured after storage. Tubers were then stored in a dark room at room temperature to allow sprouts to develop. The sprouts of each tuber were counted and weighed. Weight loss was the lowest for tubers stored at 3oC. Firmness of the tubers increased as the Ca: K & Mg ratio of the nutrient solution used during production was increased. Number of sprouts was the highest for tubers stored at 6oC. Sprout number was also significantly higher for the larger tubers compared to the smaller ones. Total sprout weight was the highest for the tubers stored at 6oC, and was also the highest for the larger tubers. After sprouts started to develop, the tubers were planted again in the greenhouse, in sawdust and irrigated with a complete Steiner nutrient solution at 1.5 mS cm-1. After these plants were harvested, the leaf area and dry weight of the leaves were determined. The first generation tubers were counted and weighed. The only factor that had a significant influence on the growth of the plants, was the size of the seed tubers that were used. The larger seed tubers produced plants that had significantly higher leaf areas, dry weight of leaves, as well as higher yields than that of the plants produced from the smaller seed tubers. From the results of this study, it can be concluded that Ca has a definite positive effect on the quality of seed potatoes as well as the size of the tubers that are produced. This study also supported that seed tubers should be stored at low temperatures, around 3oC, to maintain the highest quality, while larger tubers proved to out-yield smaller ones.