Thesis (MScAgric)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Biochar is a carbon-rich solid material produced during pyrolysis, which is the thermal degradation of biomass under oxygen limited conditions. Biochar can be used as a soil amendment to increase the agronomic productivity of low potential soils. The aim of this study was to investigate the effect of applying locally-produced biochar on the fertility of low-nutrient holding, sandy soil from the Western Cape, and to determine the optimum biochar application level. Furthermore, this study investigates the effect of biochar on the leaching of an inorganic nitrogen fertilizer and a multi-element fertilizer from the sandy soil. The biochar used in this study was produced from pinewood sawmill waste using slow pyrolysis (450 °C). The soil used was a leached, acidic, sandy soil from Brackenfell, Western Cape. In the first study, the sandy soil mixed with five different levels of biochar (0, 0.05, 0.5, 0.5 and 10.0 % w/w) was chemically characterised. Total carbon and nitrogen, pH, CEC and plant-available nutrients and toxins were determined. The application of biochar resulted in a significant increase in soil pH, exchangeable basic cations, phosphorus and water holding capacity. A wheat pot trial using the biochar-amended soil was carried out for 12 weeks and to maturity (reached at 22 weeks). The trial was conducted with and without the addition of a water-soluble broad spectrum fertilizer. Results showed that biochar improved wheat biomass production when added at low levels. The optimum biochar application level in the wheat pot trial was 0.5 % (approximately 10 t ha-1 to a depth of 15 cm) for the fertilized treatments (21 % biomass increase), and 2.5 % (approximately 50 t ha-1 to a depth of 15 cm) for unfertilized treatments (29 % biomass increase). Since most biochars are alkaline and have a high C:N ratio, caution should be taken when applying it on poorly buffered sandy soil or without the addition of sufficient nitrogen to prevent nutrient deficiencies. In the second study, leaching columns packed with sandy soil and biochar (0, 0.5, 2.5 and 10.0 % w/w) were set up to determine the effect of biochar on inorganic nitrogen fertilizer leaching over a period of 6 weeks. It was found that biochar (0.5, 2.5, and 10.0 % w/w) significantly reduced the leaching of ammonium (12, 50 and 86 % respectively) and nitrate (26, 42 and 95 % respectively) fertilizer from the sandy soil. Moreover, biochar (0.5 %) significantly reduced the leaching of basic cations, phosphorus and certain micronutrients. This study demonstrated the potential of biochar as an amendment of acidic, sandy soils. Our findings suggest that an application rate of 10 t ha-1 should not be exceeded when applying biochar on these soils. Furthermore, biochar application can significantly reduce nutrient leaching in sandy agricultural soils. / AFRIKAANSE OPSOMMING: Biochar is ʼn koolstof-ryke, soliede materiaal geproduseer gedurende pirolise, wat die termiese degradasie van biomassa onder suurstof-beperkte omstandighede behels. Biochar kan gebruik word as ʼn grondverbeterings middel om die agronomiese produktiwiteit van grond te verhoog. Die doel van hierdie studie was om die effek van plaaslike vervaardigde biochar op die vrugbaarheid van die sanderige grond van die Wes-Kaap te ondersoek, en om die optimale biochar toedieningsvlak te bepaal. Verder, het hierdie studie die effek van biochar op die loging van anorganiese stikstof kunsmis en ‘n multi-elementkunsmis op sanderige grond ondersoek. Die biochar wat in hierdie studie gebruik is, is van dennehout saagmeul afval vervaardig d.m.v. stadige pirolise (450 °C). Die grond wat in hierdie studie gebruik is, is ‘n geloogde, suur, sanderige grond van Brackenfell, Wes-Kaap. In die eerste studie, is ‘n chemiesie ondersoek van die sanderige grond wat vermeng met is met vyf verskillende vlakke van biochar (0, 0.05, 0.5 en 10.0 % w/w) uitgevoer. Totale koolstof en stikstof, pH, KUK, en plant-beskikbare voedingstowwe en toksiene is in die grondmengsels bepaal. Die toediening van biochar het ‘n veroorsaak dat die grond pH, uitruilbare basiese katione, fosfor en waterhouvermoë beduidend toegeneem het. ‘n Koringpotproef was uitgevoer vir 12 weke en ook tot volwassenheid (wat op 22 weke bereik was) om die effek van die biochar op die sanderige grond teen die vyf verskillende toedieningsvlakke te bepaal. Daar was behandelings met en sonder die bykomstige toediening van ‘n wateroplosbare breë-spektrumkunsmis. Resultate toon dat die toediening van biochar teen lae vlakke koringbiomassa produksie verbeter. Die optimale biochar toedieningsvlak in die koringpotproef is 0.5 % (omtrent 10 t ha-1 tot ‘n diepte van 15 cm) vir die bemeste behandeling (21 % biomassa toename), en 2.5 % (omtrent 50 t ha-1 na ‘n diepte van 15 cm) vir onbemeste behandelings (29 % biomassa toename). Aangesien die meeste biochars alkalies is en ‘n hoë C:N verhouding besit, moet sorg gedra word wanneer dit op swak-gebufferde of lae N-houdende sanderige gronde toegedien word. Die resultate het aangedui dat die biochar versigtig aangewend moet word om grond oorbekalking te voorkom. In die tweede studie, was kolomme gepak met 2.0 kg van die sanderige grond gemeng met biochar (0, 0.05, 0.5, 2.5 en 10.0 % w/w) om die effek van biochar op die loging die anorganiese stikstof kunsmis oor ‘n tydperk van 6 weke om vas te stel. Daar is gevind dat biochar (0.5, 2.5 en 10.0 % w/w) die loging van ammonium (12, 50 en 86 % onderskeidelik) en nitraat (26, 42 en 95 % onderskeidelik) op sanderige grond aansienliek verminder. Verder, het biochar (0.5 %) die loging van basiese katione, fosfor en mikrovoedingstowwe aansienlik verminder. Hierdie studie het die potensiaal van biochar as verbeteringmiddel van suur, sanderige grond gedemonstreer. Ons bevindinge dui daarop aan dat ‘n toepassing vlak van 10 t ha-1 moet nie oorskry word nie wanneer biochar op hierdie gronde toegedien word. Die toediening van biochar op sanderige grond kan die loging van voedingstowwe aansienlik verlaag.

Thesis (MScAgric)--Stellenbosch University, 2012 / ENGLISH ABSTRACT: Biochar has been labelled to be a key factor in the global carbon mitigation act and has been described as the modern day equivalent (terra nova) to the terra preta dark earth soils of the Brazilian Amazon. Globally biochar has been evaluated as a means to improve soil fertility and to mitigate greenhouse gases (GHGs). Little research has however been published on the effects of biochar incorporation on soil physical properties. The objective of this study was to evaluate the effect of pine sawmill waste derived biochar (locally-produced via slow pyrolysis – 450°C) on selected soil physical properties, soil-water dynamics and crop production and- performance, when amended to a Kroonstad (Kd 1000 – Morgendal) soil form. This soil form is commonly found in the Western Cape area (South Africa) and can be classified as having low agricultural suitability for perennial- and annual crop species. Two pot trials were carried out in an atmospheric controlled greenhouse, where winter wheat and green beans respectively were planted, with five different application levels of biochar (0t/ha, 1t/ha, 10t/ha, 50t/ha and 200t/ha). Soil physical properties namely, water-stable aggregates, bulk density and water-retention capacity along with physiochemical characterisation of the sandy soil and biochar was determined. The water-use was monitored throughout the trials (evapotranspiration, volumetric water content and biomass water use efficiency, BWUE). The above- and below ground (specific leaf traits for the green bean and the root structural development for the winter wheat) biomass was collected and analysed at harvest. There was significantly higher volumetric water content measured for the 50t/ha and 200t/ha biochar treatments. This effect can be ascribed due to a change in the soil’s tortuosity and porosity where more meso- and micro-pores were present as the biochar rate increased. The same results were evident when a water-retention curve was established in vitro by means of the sandbox method. The bulk densities were only significantly lower for the 200t/ha biochar treatments. The wheat root systems differed greatly among the fertilised biochar treatments: the 50t/ha and 200t/ha treatments had a more complex fibrous root system (more extensive branching and thinner roots) than 0t/ha, 1t/ha and 10t/ha application levels. This is attributed to the increased water-holding capacity along with a reduction of N- and P availability with increasing addition of biochar. Several leaf traits were measured for the green bean crops; however the leaf nitrogen- and carbon content, chlorophyll content index (CCI) and carbon isotope fractionation yielded the most interesting findings. Concerning the fertilised biochar treatments, there was established that the 10t/ha treatments had the highest leaf nitrogen- and carbon content. The leaf chlorophyll content did not differ significantly between the fertilised biochar treatments; however a very interesting observation was evident regarding the measured leaf CCI for the unfertilised treatments. A decreasing trend and lower leaf CCI was measured as the biochar application levels increased. This effect was ascribed to be due to a decrease in N uptake by the plants as the biochar application increased, the C/N ratio also increased, and this leading to N immobilisation. The lowest leaf carbon isotope fractionation was measured for the 10t/ha fertilised treatments and is inversely correlated with BWUE and therefore endorses the conclusion that the 10t/ha biochar application had a positive effect on the long term water use efficiency for the green bean plants. Biochar promoted aggregation in the sand-rhizosphere interface for winter wheat, increased water-holding capacity and enhanced crop performance for green beans. The findings reported here provide new information on the effect of biochar on the structural development of sandy soil, combined with biochar- and root growth effects for winter wheat; along with detailed interpretations of specific leaf traits associated with crop production for commercial green beans. The addition of biochar at low application levels (approximately 1-10t/ha to 15 cm depth) increased the biomass yield and water use efficiency of the crop species. Besides long term carbon storage, biochar can have immediate positive effects on the physical properties of sand and plant growth. / AFRIKAANSE OPSOMMING: Biokoolstof word beskou as ‘n sleutel komponent rakende die wet op globale koolstofvermindering en is al beskryf as die moderne ekwivalent (terra nova) van die terra preta donker-aardgronde wat aangetref word in die Brasiliaanse Amasone. Wêreldwyd word biokoolstof tans geëvalueer met die doel om grondvrugbaarheid te verbeter asook kweekhuisgasse (KHG) se nadelige gevolge te verlig. Min navorsing was tot dus ver gedoen rakende die uitwerking met toediening van biokoolstof op grondfisiese-eienskappe. Die doel van hierdie studie was om die effek van biokoolstof, wat afkomstig is van denne-saagmeul-afval (plaaslik geproduseer is en d.m.v. stadige perolise - 450°C) te evalueer aangaande die volgende faktore: geselekteerde grondfisiese-eienskappe, grond-waterdinamika interaksie en die uitwerking op gewasproduksie; met toediening aan 'n Kroonstad (Kd 1000 - Morgendal) grondvorm. Hierdie grondvorm word as algemeen in die Wes-Kaap (Suid-Afrika) bestempel en kan geklassifiseer word as ‘n lae-geskiktheid landbougrond vir meerjarige- en eenjarige gewasse. Twee potproewe is uitgevoer onder beheerde atmosfeer in ‘n kweekhuis, waar winter koring en groenbone geplant is, met vyf verskillende behandelings van biokoolstof (0t/ha, 1t/ha, 10t/ha, 50t/ha en 200t/ha). Die volgende grondfisiese-eienskappe is ondersoek, naamlik water-stabiele aggregaat formasie, bulkdigtheid en waterhouvermoë, asook die fisiochemiese karakterisering van die sanderige grond en biokoolstof wat gebuik is. Waterverbruik is gedurende die proewe gekontroleer (evapotranspirasie, volumetriese waterinhoud en die biomassa se water verbruiksdoeltreffendheid, BWVD). Die bo- en ondergrondse biomassa, spesifiek die blaareienskappe van die groenboontjie en die strukturele ontwikkeling van die winter koring se wortels, is tydens die oes ondersoek en ontleed. Die volumetriese waterinhoud was betekenisvol, asook hoër vir die 50t/ha en 200t/ha behandelings. Hierdie effek word toegeskryf as gevolg van 'n verandering in die grond se kronkeligheid en porositeit; waar meer meso- en mikroporieë teenwoordig was soos die biokoolstof inhoud toegeneem het. Dieselfde resultate was verkry met die opstelling van ‘n water-retensie kurwe in vitro d.m.v. die Sandboks metode. Bulkdigtheid was slegs betekenisvol verskilled asook aansienlik laer vir die 200t/ha biokoolstof behandelings. Die koring se wortelstelsel het drasties verskil tussen die verskillende bemeste biokoolstof behandelings: die 50t/ha en 200t/ha behandelings het 'n meer komplekse en veselagtige wortelstelsel gevorm (hoër graad van vertakking en dunner wortels was aanwesig) as die 0t/ha, 1t/ha en 10t/ha behandelings. Die effek word toegeskryf aan die toenemende waterhouvermoë, tesame met 'n tekort aan N- en P-beskikbaarheid soos die biokoolstof toedieningshoeveelhede verhoog het. Verskeie blaareienskappe is gemeet vir die groenboon gewasse, maar die blaar stikstof- en koolstof-inhoud, chlorofil inhoud indeks (CII) en koolstof-isotoop fraksionering het die mees interessante bevindinge opgelewer. Die hoogste blaar stikstof-en koolstof-inhoud is gemeet vir die 10t/ha bemeste biokoolstof behandelings. Die blaar chlorofil inhoud het nie beduidend verskil tussen die bemeste biokoolstof behandelings nie, maar daar was egter 'n baie interessante waarneming vir die onbemeste biokoolstof behandelings. ‘n Tendens was aanwesig waar die CII afgeneem het soos die biokoolstof toedieningshoeveelheid ook afgeneem het vir die onbemeste behandelings. Die effek word toegeskryf as gevolg van 'n afname in N-opname deur die plant soos die biokoolstof toedieningshoeveelheid verhoog is en tot gevolg gehad het dat die C/N-verhouding ook toegeneem het, wat gelei het tot N-immobilisasie. Die laagste blaar koolstof-isotoop fraksionering was geassioseer met die 10t/ha bemeste biokoolstof behandelings en is omgekeerd gekorreleerd met BWVD en onderskryf dus die gevolgtrekking dat die 10t/ha biokoolstof behandeling 'n positiewe uitwerking het op die langtermyn waterverbruiksdoeltreffendheid vir groenboontjie plante. Biokoolstof het aggregasie bevorder binne die wortelsone, asook deurgans die waterhouvermoë verhoog en gewasproduksie verbeter. Hierdie bevindinge lewer nuwe inligting oor die effek van biokoolstof op die strukturele ontwikkeling van sanderige grond en die gekombineerde interaksie met biokoolstof toediening en hoe dit wortegroei beïnvloed van winter koring; asook 'n gedetailleerde interpretasie van spesifieke blaareienskappe wat verband hou met die produksie van gewasse vir kommersiële verbouing soos die groenboontjie. Die toediening van biokoolstof by die lae hoeveelhede (ongeveer 1-10t/ha tot op 15 cm diepte) het die opbrengs en waterverbruiksdoeltreffendheid van die gewasse verbeter. Behalwe vir die langtermyn koolstofvaslegging, kan biokoolstof toediening onmiddellike positiewe resultate teweeg bring aangaande die fisiese eienskappe van sandgronde en plantegroei.

Thesis (MScAgric (Soil Science))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Lesotho is a country with an international reputation for the severe degree of soil erosion in its landscape. Despite several national soil conservation projects, soil erosion continues at an astounding rate. One of the reasons for this is possibly that the interactions between soil properties and erosion in Lesotho are not understood. Soil erosion is a site specific, cyclic phenomenon, controlled by geomorphological thresholds. To control soil erosion, the processes and soil properties which influence soil erosion in the specific place must be understood. In this study the soil properties of a highly eroded sub-catchment in Maphutseng, Lesotho was investigated. The gully extent in the sub-catchment, in 1957 and 2004 respectively, was mapped from aerial photos. These maps show where in the landscape gullies developed during this time. The gully maps were superimposed on maps of several soil erosion factors, to correlate the spatial distribution of the erosion factors with that of the gully distribution. A soil map was especially drawn for this. The spatial analysis shows that gully development between 1957 and 2004 was primarily confined to the area where duplex soils occur. The rest of the sub-catchment underwent negligible differences in gully extent during this time. The initiation of the gullies on the duplex soil area is ascribed to tunnel erosion. The high dispersibility of the duplex soil samples, sink holes which occur in this area and previous observations by researchers in this area gave evidence to this hypothesis. In the second part of the study the soil properties of seventeen soil profiles from across the study site were analysed. The difference in gully distribution between the duplex soils area and the rest of the catchment is ascribed to the high dispersibility of the duplex soils. No strong correlations could be found between the dispersion index and other determined soil properties. Segmented quantile regression was used to analyse the data further. Soil samples with moderate levels of total carbon (1.17%), iron oxide (0.9%) and effective cation exchange capacity (13.7 cmolc/kg), have below average dispersibility. When none of these stabilising agents are present in moderate amounts, soils with even low exchangeable sodium percentage values (0.68%) are dispersive. Furthermore, soils which have developed in colluvial material from basaltic origin were found to be less dispersive, presumably because of the amorphous clay minerals present in the volcanic material. The colour and increase in clay content between the A and B horizons of a soil can indicate the tunnel erosion potential of the soil. Dark coloured soils (values less than 4 and chromas less than 3) were found to have low dispersibility and free water can accumulate in the subsoils where the B horizon has much more clay than the A horizon. The accumulation of free water in the subsoil is necessary for tunnel formation. Thus soils with dark colours and/or a low clay accumulation index have low tunnel erosion potential. / AFRIKAANSE OPSOMMING: Lesotho is ‘n land met ‘n internasionale reputasie vir die ernstige graad van gronderosie waaronder die landskap gebuk gaan. Ten spyte van verskeie nasionale grondbewaringsprojekte duur die erosie teen ‘n verstommende tempo voort. Een van die redes hiervoor is heel moontlik dat die interaksies tussen grondeienskappe en erosie in Lesotho nie verstaan word nie. Gronderosie is ‘n plekspesifieke, sikliese verskynsel, wat deur geomorfologiese drempelwaardes beheer word. Om gronderosie te bekamp moet die prosesse en grondeienskappe wat gronderosie in die spesifieke plek beïnvloed, geïdentifiseer en verstaan word. In hierdie studie is die grondeienskappe van ‘n hoogs geërodeerde opvanggebied in Maphutseng, Lesotho ondersoek. Die dongaverspreiding in die opvanggebied, in 1957 en 2004 respektiewelik, is vanaf lugfoto’s gekarteer. Die kaarte wys waar in die landskap dongas gedurende hierdie tyd ontwikkel het. Die dongakaarte is op kaarte van verskeie gronderosie faktore gesuperponeer om die ruimtelike verspreiding van die erosie faktore met die donga verspreiding te korreleer. ‘n Grondkaart is spesiaal vir hierdie doel opgestel. Hierdie analise het gewys dat donga-ontwikkeling tussen 1957 en 2004 hoofsaaklik op die area waar dupleks gronde voorkom plaasgevind het. Die res van die opvanggebied het weinig verskille in donga verspreiding in hierdie tyd ondergaan. Die ontstaan van die dongas in die dupleksgronde word toegeskryf aan tonnelerosie. Die hoë dispergeerbaarheid van die dupleks grondmonsters, sinkgate wat in die area voorkom en vorige waarnemings deur navorsers in die area verleen bewyse aan hierdie hipotese. In die tweede deel van die studie is die grondeienskappe van sewentien grondprofiele van regoor die opvanggebied ontleed. Die verskil in donga verspreiding tussen die dupleksgrond area en die res van die opvanggebied is toeskryfbaar aan die hoë dispergeerbaarheid van die dupleks gronde. Geen sterk korrelasies is tussen die dispersiwiteits indeks en ander bepaalde grondeienskappe gevind nie. Gesegmenteerde kwantiel regressie is gebruik om die data verder te ontleed. Hierdie ontleding het gewys dat grondmonsters met matige vlakke van totale koolstof (1.17%), ysteroksied (0.9%) en effektiewe katioonuitruilkapasiteit (13.7 cmolc/kg), ondergemiddelde dispergeerbaarheid toon. Waar nie een van hierdie stabiliserings agente in matige hoeveelhede voorkom nie, is selfs gronde met baie lae uitruilbare natriumpersentasie waardes (0.68%) dispersief. Daar is ook gevind dat gronde wat vanuit kolluviale basaltiese afsettings ontwikkel het, minder dispersief is. Die kleur en verskil in klei persentasie tussen die A en B horison van ‘n grond kan as aanduiding dien van die grond se potensiaal vir tonnelerosie. Donker grondkleure (waarde laer as 4 en chroma laer as 3) wys op ‘n lae dispersiwiteit terwyl vrywater in die ondergrond van gronde waar die B horison veel meer klei as die E horison bevat kan akkumuleer. Die aansameling van vrywater in die ondergrond is noodsaaklik vir tonnelvorming. Dus het donker gronde en gronde met ‘n lae klei akkumulasie indeks ‘n lae potensiaal vir tonnelerosie.

Thesis (MSc)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: A study was conducted between 2000 and 2002 in the lower Berg River catchment of the semi-arid Western Cape Province to investigate the effect of irrigation developments (wheat fields to table grapes) on the quality of the Berg River as well as the sustainability of these developments. This study was necessitated by the mineralisation of both the Breede and Berg River, probably due to irrigation together with the higher pressure on these water resources from the growing demand for fresh water from the Cape Town metropolitan area. Water and Salt balances of two dominant soil patterns (Glenrosa/Swartland and Oakleaf/Hutton soil forms) from the catchment area were monitored at two localities. Vineyard blocks of different ages in the same soil forms were used to study the effect of irrigation over time. The electrical conductivity of the soil water extracts (ECe) was measured three times over depth at the selected sites and the quality of irrigation and drainage return-flow were monitored. Soil water storing capacities of these stony (high rough fragment' fractions) soils were also characterised for more efficient drainage quantity prediction. Glenrosa/Swartland soils showed the highest ECe's (200-400 mx.m") that decreased significantly after four to five years of irrigation and distribution became more uniform over depth. These high salt concentrations were explained due to natural occurrence of salts, mineral weathering and salts from the irrigation water. Oakleaf/Hutton soils showed lower ECe's « 200 nfS.m") but they are subject to the quality of the irrigation water, which is not that constant over years. Localised salt accumulation was observed due to the irrigation method and became more prominent over years. Drainage quantities were under predicted because of the big/high rough fragment fractions and the occurrence of preferential-flow. This prohibited the accurate calculation of the soil water house holding characteristics. It also led to the under calculation of salt return-flow, but it was very evident that the most salt retumflow occurred from the Glenrosa/Swartland soils. Effective irrigation management to achieve and maintain optimal soil water levels and to reduce the negative impact of high ECe's is essential for the sustainability of these irrigation developments. At present it does not seem that the irrigation return-flow is causing dramatic mineralisation of the lower Berg River, but it is a situation that must be monitored as the developments extent and become older (come into production). It seems that irrigation return-flow only has an influence on the quality of the river at the beginning of such a development, but after about three years the influence directly correlates with the quality of irrigation water and mineral weathering. / AFRIKAANSE OPSOMMING: 'n Studie is gedurende die jare 2000 tot 2002 in die benede Bergrivier opvanggebied van die semi-ariede Wes-Kaap Provinsie gedoen om die effek van besproeiingsontwikkelings (koringlande na tafeldruiwe) op die kwaliteit van die Bergrivier se water, asook die volhoubaarheid van besproeiingslandbou te ondersoek. Hierdie studie was genoodsaak deur toenemende versouting van beide die Breede- en Bergrivier, waarskynlik a.g.v. besproeiing, tesarne met groter druk op hierdie waterbronne van wee die groeiende aanvraag na vars water deur die Kaapstadse metropool. Water- en soutbalanse van twee dominante grondpatrone (Glenrosa/Swartland en Oakleaf/Hutton grondvorms) binne die opvanggebied was by twee lokaliteite gemoniteer. Wingerdblokke van verskillende ouderdomme binne dieselfde grondvorms is gebruik om die effek van besproeiing oor tyd te ondersoek. Die elektriese geleiding van die grondwaterekstrak (EGe) was drie maal op verskillende dieptes by geselekteerde persele gemeet en die kwaliteit van besproeiingswater en dreineringsterugvloei was deurgaans gemoniteer. Grondwaterstoringskapasiteite van hierdie klipryke ( hoe 'growwe fragment fraksie) gronde was ook gekarakteriseer vir meer doeltreffende voorspellings van dreineringshoeveelhede. Glenrosa/Swartland gronde het die hoogste EGe's getoon (200-400 mx.m') wat na vier tot vyf jaar se besproeiing aansienlik afgeneem het en meer uniform met diepte versprei was. Die hoe soutkonsentrasies is veroorsaak deur die natuurlike voorkoms van sout in die grond, minerale verwering en sout vanuit die besproeiingswater. Oakleaf/Hutton gronde het laer EGe's getoon « 200 mS.m-I ), maar hierdie gronde se soutinhoud is ook onderhewig aan die kwaliteit van die besproeiingswater en dreinering wat oor jare nie baie konstant was en nog is nie. Gelokaliseerde soutaansarneling tussen wingerdrye is ook waargeneem a.g.v. die besproeiingsmetode en dit word meer prominent oor jare. Dreineringshoeveelhede was onder-voorspel a.g.v. die groot/hoe growwe fragment fraksies en voorkoms van voorkeurvloei, wat die akkurate modellering van grondwaterhuishouding beperk het. Dit het ook daartoe gelei dat soutterugvloei ondervoorspel was, maar dit was duidelik dat die meeste soutterugvloei vanuit die Glenrosa/Swartland gronde plaasvind. Effektiewe besproeiingsbestuur, om optimale grondwaterpeile te handhaaf en om negatiewe effekte van hoe EGe te beperk, is noodsaaklik vir die volhoubaarheid van hierdie tipe besproeiingsontwikkelings. Tans blyk dit nie of besproeiingsterugvloei drarnatiese versouting van die benede Bergrivier veroorsaak nie, maar dit is egter 'n situasie wat deeglik gemoniteer moet word soos wat ontwikkelings uitbrei en ouer word (in produksie kom). Besproeiingsterugvloei het dus net aan die begin van so 'n ontwikkelling 'n invloed op die EG van die rivier, maar na ongeveer drie jaar hou die invloed direk verband met die kwaliteit van die besproeiingswater en minerale verwenng.

Thesis (MScAgric)--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: The study was conducted in the Western Cape Province to investigate the effect of soil preparation on selected soil physical properties. This study was necessitated by the negative effects that high soil bulk density has on the growth and production of a vine. Soil preparation in South Africa are applied to remove root limiting layers in the subsoil and to create a larger soil volume for root growth. The question is whether it is always necessary because of the destruction of macropore structure and also the high costs that is involved. The study includes different soil forms, different depths of tillage, different tillage operations and also the change of soil physical properties with time. Soil physical properties that was investigated include, bulk density (cloth method), infiltration (mini disk infiltrometer and double ring infiltrometer), shear strength (pocket vane tester), soil strength (penetrometer) and root distribution (profile wall method). The main finding was that the positive effects of soil preparation were still clear after 25 years. The bulk density, shear strength, penetration resistance and infiltration with the double ring infiltrometer of the deeper soil preparation practices were considerably lower than those of undisturbed soil. Soil preparation shallower than 60 cm recompacted more than the deeper tillage treatments. Hydraulic conductivity with the mini disk infiltrometer yielded mixed results. This was mainly because measurements represented hydraulic conductivity through the whole profile and therefore can be influenced by many factors. Root distribution has increased with depth of tillage and the effect was clear at Nietvoorbij in the deeper (> 60 cm) soil preparation treatments. There were no significant difference between the two soil preparation methods (delve plough and soilmix) at Kanonkop, although the effect of secondary compaction by the soilmix was quite clear. Recompaction over a year was clear in the 2009 and 2010 tillage treatments at Broodkraal. The methods that were used to determine the soil physical properties have all yield good results. At all the sites the tillage treatments generally yielded better results than the undisturbed soils. It was also clear that the longer the time after tillage the smaller become the difference between the tillage treatments and the undisturbed soils. Recompaction did occur and therefore soil preparation might possibly be applied again before new vines wants to be planted. / AFRIKAANSE OPSOMMING: Die studie is in die Wes-Kaap Provinsie gedoen om die effek van grondvoorbereiding op geselekteerde grondfisiese eienskappe te ondersoek. Hierdie studie is genoodsaak deur die nadelige gevolge wat hoë gronddigthede op die groei en produksie van ’n wingerdstok het. Grondvoorbereiding in Suid-Afrika word toegepas om beperkende lae in die ondergrond te verwyder en sodoende ‘n groter grondvolume vir wortelgroei beskikbaar te stel. Die vraag is egter of dit altyd noodsaaklik is weens die vernietiging van voorkeur vloeikanale en die hoë kostes wat daarmee gepaard gaan. Die studie sluit verskillende grondvorms, verskillende dieptes van bewerking en verskillende tipes bewerking in asook hoe die toestande met verloop van tyd verander. Grondfisiese eienskappe wat ondersoek is, sluit in: bulkdigtheid (kluitmetode), infiltrasie (“mini disk” - en dubbelring infiltrometer), skuifsterkte (skroefbladmeter), grondsterkte (penetrometer) en wortelverspreidings (profielwand metode). Die studie is uitgevoer by drie verskillende proeflokaliteite, nl. Nietvoorbij, Kanonkop en Broodkraal. Die vernaamste bevindings was dat die grondvoorbereidingsbehandelings se voordelige effek oor die langtermyn, na 25 jaar, steeds duidelik waarneembaar was. Die bulkdigtheid, skuifsterkte, penetrasieweerstand en infiltrasie met dubbelring infiltrometer van die dieper grondbewerkingspraktyke was aansienlik laer as die kontrole behandelings (onversteurde grond) gewees. Die grondvoorbereidingsaksies vlakker as 60 cm het tot ʼn mate weer herverdig. Hidrouliese geleiding met minidisk infiltrometer het baie wisselvallige resultate opgelewer. Dit is hoofsaaklik omdat die meting die geleiding deur die hele profiel verteenwoordig en daar baie faktore is wat dit kan beïnvloed. Die wortelverspreiding het met diepte van grondbewerking toegeneem en die langtermyn voordelige effek was duidelik by Nietvoorbij in die dieper (> 60 cm) grondvoorbereidingsbehandelings sigbaar. Die twee grondvoorbereidingspraktyke (dolbewerking en “soilmix”) by Kanonkop het nie betekenisvol van mekaar verskil nie, alhoewel die effek van sekondêre kompaksie soos veroorsaak deur die “soilmix” implement, duidelik was. Herverdigting oor die tydperk van ’n jaar was duidelik tussen die 2009- en 2010 bewerking by Broodkraal. Die metingsmetodes waarmee die grondfisiese eienskappe ondersoek is, het almal goeie resultate gelewer. By al die proeflokaliteite het die bewerkingsbehandelings oor die algemeen beter resultate as die kontrole-behandelings (onversteur) gelewer. Hoe langer die tydperk na grondvoorbereiding hoe kleiner was die verskil tussen die bewerkingsbehandelings en die kontrole. Herverdigting het wel voorgekom en daarom sal grondvoorbereiding moontlik weer toegepas moet word wanneer nuwe aanplantings gemaak word.

Thesis (MScAgric)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Soil texture, plant available water and fertilizer N would influence growth, biomass production and antimicrobial properties of locally used medicinal plants.This research was aimed at investigating how various soil textures (loamy sand, sandy loam and loam) with varying amounts of plant available water (PAW) and nitrogen fertilizer rates would influence the biomass production and antimicrobial properties of Mentha longifolia L. In this research, a two-way factorial experiment was used. It was produced by 3 X 3 factors, viz. three different soil textures (loam, sandy loam and loamy sand) and three levels of PAW in the first trial (0 %, 50 % and 90 % depletion of PAW) and three levels of N fertilizer rates in the second trial. The elemental fertilizers KNO3, K2SO4, KH2PO4, KCl Ca (NO3)2.2H2Oz, CaSO4.2H2O and Mg SO4.7H2O were used to prepare a nutrient solution for fertigation to meet 0Kg ha-1, 150Kg ha-1 and 250Kg ha-1 fertilizer N. This was replicated four times. The experiment was conducted in a tunnel. From the first trial the highest biomass production was obtained from 0% depletion of PAW treatments whereas 50% and 90% depletion of PAW matched each other at lower biomass productions. In terms of soil texture a higher biomass production was gained from loamy sand followed by loam and sandy loam. In the second trial similar influences of soil texture were evident and the significant biomass productions were highest, intermediate and low from 250Kg ha-1, 150Kg ha-1 and 0Kg ha-1 of fertilizer N, respectively. Accordingly, Mentha longifolia L revealed a minimal bacterial inhibition activity at 20g 100ml-1 against Staphylococcus aureus (gram positive bacteria) under Minimum Inhibitory Concentration assay–susceptibility test. It was therefore concluded that soil texture does influence biomass production. In a like manner, the PAW had a significant impact on the total biomass production. An increase in N fertilizer increased vegetative biomass production. Plant material obtained from Mentha longifolia L has antimicrobial properties. Medically the plant can be used to combat Staphylococcus aureus – a major and ubiquitous pathogen for humans. The significance of this study is thus that it will benefit and help the medical community and future research as the guide to sustainable production and utilization of Mentha longifolia L. / AFRIKAANSE OPSOMMING: Grondtekstuur, plant beskikbare water en kunsmis N sal plantegroei, biomassaproduksie en antimikrobiese-eienskappe van plaaslike medisinale plante affekteer. Die doel van die navorsing was om die effek van grondteksture, plant beskikbare water (PAW) en stikstof op die biomassaproduksie en antimikrobieseeienskappe van Mentha longifolia L. te bestudeer. 'n Tweerigting-faktoriaal-eksperiment is gebruik deur drie verskillende grondteksture (leem, sanderige-leemgrond en leemsand) en drie vlakke van PAW in die eerste geval (0%, 50% en 90% uitputting van PAW) en drie vlakke van N-kunsmistoedienings in die tweede geval. Die basiese kunsmis KNO3, K2SO4, KH2PO4, KClCa(NO3)2.2H2Oz, CaSO4.2H2O en MgSO4.7H2O is gebruik in so „n mate dat 0Kg ha-1, 150kg ha-1 en 250 kg ha-1 Nas sproeibemesting toegedien is. Dit is vier keer herhaal. Die eksperiment is uitgevoer in 'n tonnel. Die hoogstebiomassaproduksie is van die eerste geval verkry van 0% uitputting van PAW behandelings, terwyl 50% en 90% uitputting van PAW ooreenstem met mekaar op laer biomassaproduksies. In terme van grondtekstuur is 'n hoër biomassaproduksie verkry in leemsand gevolg deur leem en sanderigeleem. In die tweede geval is soortgelyke invloede van grondtekstuur duidelik en die beduidende biomassaproduksies was die hoogste, intermediêre en laagste van 250 kg ha-1, 150kg ha-1 en 0Kg ha-1 van kunsmis N, onderskeidelik. Gevolglik, Mentha longifolia L onthul 'n minimale bakteriese inhibisie aktiwiteit op 20g 100ml-1 teen Staphylococcus aureus (gram positiewebakterieë) onder Minimum inhiberende konsentrasie assay-vatbaarheidtoets. Die gevolgtrekking is dus dat grondtekstuu biomassaproduksie beïnvloed. In 'n soortgelykewyse, het PAW 'n beduidende impak op die totale biomassaproduksie. 'n Toename in N-kunsmis verhoog vegetatiewe biomassaproduksie. Plantmateriaalverkry van Mentha longifolia L het antimikrobiale-eienskappe en kan as Die medisinale plante gebruik word om Staphylococcus aureus te bestry - 'n groot en alomteenwoordige patogeen in die mens. Die belangrikste bydrae van die navorsing is die bydra wat dit tot die mediesegemeenskap gemaak het. Die studie het ook riglyne gestel vir toekomstige navorsing vir volhoubare produksie van Mentha longifolia L. / NRF and DST for the funding of this study through the Seboka Project

Thesis (MScAgric (Viticulture and Oenology))--University of Stellenbosch, 2007. / The South African and international table grape industries are growing rapidly, which necessitates the production of high quality export fruit at competitive production costs. For this reason, alternative irrigation methods are required to utilise water optimally while still attaining good quality table grapes. An increase in agricultural productivity may be dependent on either the availability of more water for irrigation or an increase in the efficiency of water use. The first aim of this study was to evaluate the effectiveness of the Partial Rootzone Drying (PRD) irrigation strategy in Crimson Seedless and Dauphine table grape production. This irrigation system is based on the drying of half of the vine roots, thereby allowing the plant to produce hormones like abscisic acid (ABA) in reaction to water stress. The hormone production in turn results in stomatal closure and the reduction of water loss via transpiration. The drying cycle is then repeated after 10 to 15 days on the other side of the vine, irrigating the previously dried roots. PRD will encourage a consistent production of the stress hormone abscisic acid (ABA), without actual water stress. This strategy reduces the amount of water used for irrigation, without an accompanying loss in fruit yield, as compared to conventional techniques. In this study, conventionally treated vines were irrigated according to historical block data and PRD-treated vines were irrigated at the same times. The second aim of this study was to monitor the efficacy of a foliar nutrient, Croplife. This foliar nutrient allegedly improves the uptake of foliar applied nutrients, assists with transport of all minerals through the leaves and enables the plant to attain higher pest and disease resistance thresholds. Conventionally treated vines that did not receive foliar nutrient treatment were compared to vines that received foliar nutrients as prescribed by the manufacturer. Vine cultivars Crimson Seedless and Dauphine, were grown under open hydroponic principles with drip and drip irrigation respectively in this experiment. For the hydroponic vines (Crimson Seedless), all vines were situated in the same row and 72 vines were divided into mini-plots of three vines. Treatments were then assigned to an equal number of plots at random. The same procedure was followed for the drip irrigated vines (Dauphine) but the vines were situated in two rows of equal length. Treatment effects were followed from budburst until harvest, where after post-harvest analyses were conducted. The first aim, namely to show that PRD is an effective irrigation strategy for table grape production in Crimson Seedless and Dauphine cultivars , has shown that vines did not exhibit signs of stress even though they received only half the conventional amount of water. This study was conducted over only one growth season and therefore no definite conclusions could be drawn about the long term effectiveness of PRD on table grapes. It did, however, confirm numerous results obtained from different studies on the use of PRD in wine grape production. The results obtained in the second part of the study were inconclusive and could not show that Croplife is effective in improving the uptake and transport of applied foliar nutrients. Because Crimson Seedless is cultivated under open hydroponic principles, nutrients can be absorbed by the roots via the soil and micronutrients are also available from chemical sprays during the season. There was no evidence to indicate that the use of Croplife increased nutrient absorption and transport, neither did it supplement or detract form the observed effect of PRD. Despite the limitations experienced during this study, it has shown that the use of PRD for table grape production may be a useful tool for improving water utilisation efficiency in future. The strategy will have to be developed systematically through experimentation to fully unlock the potential of the PRD management system for table grape production. This study provides a good starting point for future research required to elucidate numerous aspects of the PRD system and has clearly shown that established vineyards can be switched to a PRD system without a loss in table grape quality. It is envisaged that the advantages of this system could have a positive effect on the production of high quality fruit for the international market.

Thesis (MscAgric (Viticulture and Oenology))--University of Stellenbosch, 2009. / ENGLISH ABSTRACT: Tannins and colour components in red wine are important quality parameters. These factors can be manipulated in the vineyard by grape growing techniques or in the cellar by different winemaking practices. Grape seeds make a significant contribution to tannin concentration in wine when compared to those from the skins and pulp. Tannins contribute to the ageing potential, organoleptic properties and stabilisation of red wine colour. The colour of a red wine is also influenced by malolactic fermentation, the biological process that transforms malic acid into lactic acid which normally leads to an increase in pH. The subsequent change in pH alters the anthocyanin equilibrium, the primary colour components in red wine. Oxygen contributes to the polymerisation of anthocyanins over time to form more stable pigments that are less sensitive to pH fluctuations and sulphur dioxide bleaching. Limited research has been done on the use of oxygen after alcoholic fermentation and the impact it has on the phenolic composition of red wines. Similarly, only a few studies have examined the impact of either the addition or removal of seeds to the phenolic composition of a red wine in combination with oxygen addition. Additionally, little published data seems to exist on the effect of different pHs on red wine’s phenolic and colour development after oxygen addition. In our results we have shown that it is possible to stabilise wine colour by adding supplementary seeds before alcoholic fermentation. This led to an increase in colour intensity in certain cases. Some red wines produced without seeds had significantly lower colour intensities. This clearly suggests that catechins and proanthocyanidins are extracted from seeds and contribute to wine colour as they combine with other pigments to stabilise wine colour. Spectrophotometric and HPLC analyses have shown that the total phenolic content increased with seed concentration. However, we have observed that a wine may possibly become saturated with phenols when supplementary seeds are added. Anthocyanin concentrations often decreased when oxygen was added, while polymeric phenols and polymeric pigments sometimes increased. When applying different oxygen dosages to a red wine on commercial scale with microoxygenation, it was found that monomeric anthocyanins decreased as more oxygen was added and this decrease in anthocyanins led to the formation of stable polymeric pigments. This was reflected in the significant increase in colour intensity for the wines receiving oxygen. Small differences were detected in the total phenol and tannin concentration for the control and oxygenated wines. However, some of these phenolic and colour differences disappeared during subsequent ageing of the wine. When making wines of different initial pHs, we observed that the colour density decreased as the pH increased. The application of oxygen reduced the decrease in colour during MLF, especially at a lower pH. The addition of oxygen did not result in significantly different polymeric pigment concentrations in the various pH treatments, although the results could have been different if the wines were aged. However, pH differences in the range between 3.4 and 4.0 did not significantly influence the phenol composition of the wines under our conditions. This study led to a better understanding on the effect of oxygen additions under different conditions on red wine's phenolic and colour composition. / AFRIKAANSE OPSOMMING: Tanniene en kleur komponente teenwoordig in rooiwyn is belangrike kwaliteit parameters. Hierdie faktore wat wynkwaliteit beïnvloed kan gemanipuleer word in die wingerd deur verskeie verbouingstegnieke toe te pas en in die kelder deur die toepassing van verskillende wynbereidingsmetodes. Die bydrae van sade tot die finale tannienkonsentrasie in rooiwyn is groot in vergelyking met dié van die pulp en doppe. Tanniene dra by tot die verouderingspotensiaal, organoleptiese eienskappe en die stabilisasie van die wynkleur. Die kleur van ‘n rooi wyn word ook beïnvloed deur appelmelksuurgisting (AMG), die biologiese proses wat appelsuur omskakel na melksuur en ‘n gevolglike toename in die pH van die wyn veroorsaak. Hierdie verandering in die pH van die wyn beïnvloed die antosianien ewewig, die primêre kleur komponente teenwoordig in rooiwyn. Suurstof dra by tot die polimerisasie van antosianiene oor tyd om meer stabiele kleur pigmente te vorm met ‘n hoër kleurintensiteit wat minder sensitief is teenoor pH veranderinge en die bleikingseffek van swaweldioksied. Beperkte navorsing is gedoen op die gebruik van suurstof na alkoholiese gisting en die impak daarvan op die fenoliese samestelling van ‘n rooiwyn. Slegs ‘n paar studies het die invloed van die verwydering of byvoeging van sade in kombinasie met suurstoftoediening op ‘n rooiwyn se fenoliese samestelling ondersoek. Dit wil voorkom of beperkte gepubliseerde data beskikbaar is oor die effek wat verskillende pH’s het op rooi wyn se fenoliese en kleurontwikkeling na suurstof byvoeging. Ons resultate het aangedui dat dit wel moontlik is om in sekere gevalle die kleur van ‘n rooiwyn te stabiliseer deur addisionele sade by te voeg voor alkoholiese fermentasie. Hierdie byvoeging het ‘n toename in kleurintensiteit tot gevolg gehad. Sekere wyne wat gemaak is sonder sade het ‘n kenmerkend laer kleur intensiteit gehad. Hierdie bevinding is ‘n duidelike bewys dat katesjiene en prosianidiene geëkstraheer word vanuit die sade en bydra tot wynkleur deurdat hulle met ander pigmente verbind om die kleur sodoende te stabiliseer. Spektrofotometriese en hoë druk vloeistof chromatografie (HDVC) analises het gewys dat die totale fenoliese konsentrasie neem toe met ‘n toename in saad konsentrasie. Daar is egter waargeneem dat ‘n wyn moontlik versadig kan raak met fenole wanneer addisionele sade bygevoeg word. Antosianien konsentrasies het meestal afgeneem wanneer suurstof bygevoeg is, maar polimeriese fenole en polimeriese pigmente het partykeer toegeneem. Met die toediening van verskillende suurstof dosisse tot ‘n rooiwyn op kommersiële skaal het ons bevind dat monomeriese antosianiene afneem wanneer meer suurstof bygevoeg word. Hierdie afname in antosianiene het egter gelei tot die vorming van stabiele polimeriese pigmente. Dié bevinding was gereflekteer in die toename in kleurintensiteit van wyne wat met suurstof behandel is. Klein verskille was waargeneem vir die totale fenol en tannien konsentrasies tussen die kontrole en wyne behandel met suurstof. Sekere van hierdie fenoliese kleur verskille het egter afgeneem tydens die daaropvolgende veroudering van die wyne. Wyne wat gemaak is met verskillende aanvanklike pH’s se kleurintensiteit neem af soos die pH toeneem. Die toediening van suurstof het die kleurverlies tydens AMG verminder, veral by ‘n laer pH. Die toediening van suurstof het nie verskillende polimeriese pigment konsentrasies by verskillende pH’s veroorsaak nie, maar ‘n verskil kon moontlik waargeneem word indien die wyne verouder was. pH verskille tussen 3.4 en 4.0 het egter nie die fenoliese samestelling van die wyne onder ons omstandighede beduidend beïnvloed nie. Hierdie studie het gelei tot meer kennis oor die effek van suurstoftoedienings onder verskillende kondisies op rooiwyn se fenoliese en kleursamestelling.

Thesis (MScAgric)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Glutathione (GSH), a tripeptide consisting of glutamate, cysteine and glycine, is the most ubiquitous non‐protein intracellular thiol in a large variety of organisms, including plants, animals and fungi. The thiol moiety of the cysteine residue confers unique redox and nucleophilic properties. In plant cells, GSH fulfils an indispensible role in the antioxidant system, sulphur metabolism and detoxification of xenobiotics. Upon grape crushing, GSH is extracted into the juice where it exerts several protective effects during the vinification process. In must, it reacts with oxidized phenolic compounds to form the colourless grape reaction product (GRP) which limits must browning to a certain extent. During wine ageing, GSH impedes the decrease of important aroma compounds, including certain esters, terpenes and volatile thiols, while at the same time preventing the development of atypical ageing off‐flavours. GSH may also inhibit the yellowing of wine during ageing. It is thus evident that elevated GSH levels in wine, in particular white wine which is more sensitive to oxidation, may be highly valuable for wine quality. The reductive crushing and pressing of white grape varieties, which limits oxidation and the consequent incorporation of GSH into GRP, promotes higher GSH levels in the juice. The reductive handling of juice also limits the formation of oxidized glutathione (GSSG). However, during alcoholic fermentation and maturation, levels generally decrease as a result of assimilation by the yeast Saccharomyces cerevisiae, and inevitable oxidation that takes place during the vinification process. The principal focus of this study was to gain a better understanding of the fate of glutathione during alcoholic fermentation and to establish whether certain oenological applications could result in elevated wine GSH levels. The application studied, included choice of yeast strain, extended lees contact, nitrogen supplementation and supplementation with glutathione enriched inactive dry yeast preparations (GHS‐IDYs). In addition, the need for a rapid analytical method for the simultaneous quantification of both GSH and GSSG in must and wine which does not involve derivatization or require extensive sample preparation, led to the development of a novel UPLC‐MS/MS method. The method was also employed to determine intracellular GSH and GSSG contents of the yeast S. cerevisiae and was studied for the first time in winemaking conditions. It was shown that the GSH levels fluctuated during alcoholic fermentation, suggesting the uptake and release by yeast. At the end of alcoholic fermentation, levels were generally lower than those initially present in grape juice, but in some cases, concentration increases were also observed. This finding indicates that, in some cases, endogenously‐produced GSH may be secreted into must during alcoholic fermentation, contributing to higher GSH levels in wine. Albeit small, significant differences in GSH content could be seen in wines fermented with different yeast strains, implying that yeast strain may to a certain extent influence wine GSH levels. While the effects of lees ageing and nitrogen supplementation seem to be insignificant in contributing to higher GSH levels in wine, the supplementation of must with GSH‐IDYs could result in increased wine GSH levels, provided the supplementation is done early during fermentation. This study has broadened our knowledge of several oenological factors, influencing GSH levels in wine and provided a new baseline for future research studies. / AFRIKAANSE OPSOMMING: Glutatioon (GSH), ’n tripeptied bestaande uit glutamaat, sisteïen en glisien, is die mees algemene nieproteïenagtige intrasellulêre tiool in ‘n wye verskeidenheid organismes, insluitende plante, diere en fungi. Die tioolfunksiegedeelte van die sisteïenresidu verleen unieke redoks‐ en nukleofiliese eienskappe. GSH vervul ‘n onmisbare rol in die antioksidantsisteem, swaelmetabolisme en die ontgiftiging van xenobiotika in plantselle. Tydens die maal van druiwe word glutatioon in die sap geëkstraeer waar dit verskeie beskermende effekte tydens die wynbereidingsproses uitoefen. GSH reageer met geöksideerde fenoliese verbindings om die kleurlose druifreaksieproduk (DRP) te vorm wat die verbruining van mos in ‘n sekere mate beperk. GSH verminder ook die afname van belangrike aromaverbindings tydens wynveroudering, insluitende sekere esters, terpene en vlugtige tiole, terwyl dit terselfdertyd die vorming van atipiese verouderingswangeure belemmer. So ook kan GSH die vergeling van wyn tydens veroudering inhibeer. Dit is dus voor die hand liggend that verhoogde GSH‐vlakke in wyn, in die besonder witwyn, wat meer oksidasie‐sensitief is, van waarde kan wees vir wynkwaliteit. Die reduktiewe maal en pers van witdruifvariëteite wat oksidasie en gevolglike inkorporasie van GSH in DRP beperk, bevorder hoër GSH‐vlakke in sap. So ook beperk die reduktiewe behandeling van sap die vorming van geoksideerde glutatioon (GSSG). Gedurende alkoholiese gisting en veroudering neem GSH‐vlakke egter af as gevolg van assimilasie deur die gis, Saccaromyces cerevisiae, asook onvermydelike oksidasie wat gedurende die wynbereidingsproses plaasvind. Die hooffokus van die studie was om ‘n beter begrip van die lot van glutatioon tydens alkoholiese gisting te verkry en om vas te stel of sekere wynkundige praktyke verhoogde GSH‐vlakke in wyn tot gevolg kan hê. Die studie het gisraskeuse, verlengde gismoerkontak, stikstofaanvulling en aanvulling met glutatioon‐verrykte, onaktiewe droëgis ingesluit. Daarbenewens het die behoefte aan ‘n vinnige analitiese metode vir die gelyktydige kwantifisering van sowel GSH as GSSG in mos en wyn wat nie derivatisering of uitgebreide monstervoorbereiding vereis nie, gelei tot die ontwikkeling van ‘n nuwe UPLC‐MS/MS metode. Hierdie metode is ook gebruik om die intrasellulêre GSH‐ en GSSG‐inhoud van die gis S. cerevisiae te bepaal wat vir die eerste keer in wynbereiding bestudeer is. Daar is bewys dat GSH‐vlakke tydens alkolholiese gisting fluktueer, wat dui op die opname en vrystelling daarvan deur die gis. Die vlakke aan die einde van alkoholiese gisting was oor die algemeen laer as vlakke aanvanklik teenwoordig in die sap. In sommige gevalle is konsentrasietoenames egter ook waargeneem. Hierdie bevinding dui daarop dat intrasellulêr‐vervaardige GSH, in sommige gevalle, in die mos uitgeskei kan word, wat tot hoër GSH‐vlakke in wyn lei. Klein, dog beduidende verskille in GSHinhoud is waargeneem in wyne wat met verskillende gisrasse berei is, wat daarop dui dat gisras in ‘n sekere mate die GSH‐vlakke in wyn kan beïnvloed. Alhoewel die effek van gismoerveroudering en stikstofaanvulling onbeduidend is, kan die aanvulling van mos met glutatioon‐verrykte, onaktiewe droëgis tot verhoogde GSH‐vlakke in wyn lei, mits die aanvulling vroeg tydens alkoholiese gisting gedoen word. Hierdie studie verbreed ons kennis van verskeie wynkundige praktyke wat GSH‐vlakke in wyn beïnvloed en vorm ‘n nuwe basis vir toekomstige navorsingstudies.

Thesis (MscAgric (Viticulture and Oenology))--University of Stellenbosch, 2009. / South Africa is the eighth largest wine producing country in the world and face stiff competition on the world market. Cabernet Sauvignon is the most planted red cultivar in the world as well as in South Africa and can be seen as the wine by which countries are judged. The aim of this study was to investigate suitable, practical maturity parameters or combinations thereof to determine the optimal time to harvest Cabernet Sauvignon grapes under South African conditions. The following parameters were investigated during this study: seed lignification, maturity indexes, anthocyanin concentration per berry, sensory criteria (grape skins tasting and wine) and phenolic content. Berry development in four Cabernet Sauvignon vineyards in different South African winegrowing areas were investigated over the 2003, 2004 and 2005 seasons. The first parameter to be investigated was seed lignification percentages. Seasonal differences at commercial harvest were observed with values of 2004 varying between 73% and 91% compared to 59% and 80% for the 2003 and 2005 seasons but commercial harvest was two weeks later during the 2004 season. During this study it was found that seeds never reached 100% lignification for Cabernet Sauvignon as was found in previous work to indicate grape maturity. The development of anthocyanins also peaked well before the maximum seed lignification was reached. It therefore appears that seed lignification is not suitable for the determination of grape maturity for Cabernet Sauvignon grapes under South African conditions. The second parameter to be investigated was maturity indexes (Balling / Titratable Acidity (TA), Balling × pH, Balling × pH2). The best wine values were used to determine the optimal maturity index values. Morgenster was the only vineyard to consistently give values that corresponded to previously reported data (index values). Anhöhe and Plaisir de Merle reported higher maturity values than that reported in literature and seasonal variation was observed. Maturity index values for the best wines varied between 88 and 101 (Balling × pH) for Anhöhe during 2003 and 2005 seasons, but increased too between 97 and 107 (Balling × pH) for 2004. The maturity index values were found to be vineyard and season dependant, with warmer areas reaching higher values. From this study it appears that maturity index values as a singular maturity parameter does not give a good indication of berry maturity in all seasons or vineyards. Thirdly, the berry anthocyanin concentration (mg / berry and mg / g berry) were investigated and comparable trends were found between the four vineyards. However vineyards in warmer, drier regions (Anhöhe) tended to have higher anthocyanin concentrations per gram berry. The more vigorous vineyard of Morgenster consistently exhibited a higher anthocyanin concentration per berry. This can be explained by the ratio of skin to pulp between small berries (Anhöhe, 0.95 g - 2004) and larger berries South Africa is the eighth largest wine producing country in the world and face stiff competition on the world market. Cabernet Sauvignon is the most planted red cultivar in the world as well as in South Africa and can be seen as the wine by which countries are judged. The aim of this study was to investigate suitable, practical maturity parameters or combinations thereof to determine the optimal time to harvest Cabernet Sauvignon grapes under South African conditions. The following parameters were investigated during this study: seed lignification, maturity indexes, anthocyanin concentration per berry, sensory criteria (grape skins tasting and wine) and phenolic content. Berry development in four Cabernet Sauvignon vineyards in different South African winegrowing areas were investigated over the 2003, 2004 and 2005 seasons. The first parameter to be investigated was seed lignification percentages. Seasonal differences at commercial harvest were observed with values of 2004 varying between 73% and 91% compared to 59% and 80% for the 2003 and 2005 seasons but commercial harvest was two weeks later during the 2004 season. During this study it was found that seeds never reached 100% lignification for Cabernet Sauvignon as was found in previous work to indicate grape maturity. The development of anthocyanins also peaked well before the maximum seed lignification was reached. It therefore appears that seed lignification is not suitable for the determination of grape maturity for Cabernet Sauvignon grapes under South African conditions. The second parameter to be investigated was maturity indexes (Balling / Titratable Acidity (TA), Balling × pH, Balling × pH2). The best wine values were used to determine the optimal maturity index values. Morgenster was the only vineyard to consistently give values that corresponded to previously reported data (index values). Anhöhe and Plaisir de Merle reported higher maturity values than that reported in literature and seasonal variation was observed. Maturity index values for the best wines varied between 88 and 101 (Balling × pH) for Anhöhe during 2003 and 2005 seasons, but increased too between 97 and 107 (Balling × pH) for 2004. The maturity index values were found to be vineyard and season dependant, with warmer areas reaching higher values. From this study it appears that maturity index values as a singular maturity parameter does not give a good indication of berry maturity in all seasons or vineyards. Thirdly, the berry anthocyanin concentration (mg / berry and mg / g berry) were investigated and comparable trends were found between the four vineyards. However vineyards in warmer, drier regions (Anhöhe) tended to have higher anthocyanin concentrations per gram berry. The more vigorous vineyard of Morgenster consistently exhibited a higher anthocyanin concentration per berry. This can be explained by the ratio of skin to pulp between small berries (Anhöhe, 0.95 g - 2004) and larger berries (Morgenster, 1.82 g – 2004). Wine colour density (A420+A520) followed the same trend as the anthocyanin concentrations of the homogenate. Grape skins (G) were used to make an artificial wine that was evaluated by an expert panel to determine the development of the grapes. Wines (W) made from sampled batches were also evaluated by an expert panel for: colour intensity, vegetative, red berry, black berry with spice, acidity, astringency and general quality. Vegetative aromas and acidity decreased and red and black berry with spice increased during ripening for both berries and wine. Colour intensity also increased, corresponding to an increase in perceived general quality score. Correlations between general quality of both the grape skins tasting and wines were investigated. Balling showed a strong correlation with general quality of the grape skins tasting (r = 0.76; p = 0.00) but not as strongly with subsequent wines (r = 0.57; p = 0.00). Anthocyanin concentration (mg / g berry) of the berries (r = 0.36; p = 0.00), perceived colour intensity of grapes (r = 0.69; p = 0.00) and wine (r = 0.84; p = 0.00) correlated with general wine quality. The tasting panel identified wines that were statically better than the rest for each season and vineyard. Maximum berry anthocyanin concentration coincided with wines rated as the best by the tasting panel. More than one wine was identified during the maximum anthocyanin peak that did not differ statistically from the best wine. It appears from this study that a window period exists at the maximum anthocyanin peak, where wines of comparable quality, but different style, can be produced. Principal component analysis (PCA) was used to determine the least number of suitable parameters that could distinguish between unripe and ripe grapes in order to establish a grape maturity model. These differences were successfully described by Balling, TA, pH, potassium (K+), tartaric and malic acid. Anthocyanin concentration could further distinguish between ripe and overripe grapes in the model. From these parameters the minimum and maximum values were used to construct a universal ripeness model containing data from all four vineyards. Variation between the four vineyards caused too much overlapping in the universal model data as the vineyards were situated in different climatic regions according to the Winkler temperature model. On a per vineyard basis this did not occur to the same extend. The best rated Cabernet Sauvignon wines correlated strongly with soluble solid content; colour and quality perceptions of grapes, but large seasonal differences resulted in larger grape compositional variances than that of the individual vineyards in the different climatic zones. This illustrated the difficulty of pinpointing a specific parameter to indicate optimal ripeness. From this study it is clear that a universal maturity model for Cabernet Sauvignon berries is not attainable at present, but individual vineyard models shows the most potential. A preliminary study into the differences of the phenolic composition was done using reverse phase high performance liquid chromatography (RP-HPLC) on the homogenate and wine. Malvidin-3-glucoside and total anthocyanins followed comparable trends to that found for the Iland method. Strong correlations (r > 0.9) were found between the malvidin- 3-glucoside and malvidin-3-glucoside-acetate and p-coumarate; this was also true for the total anthocyanins in both homogenate and wine. Wines identified by a tasting panel to be the best quality, corresponded with the maximum anthocyanin concentration (mg / L) peak in the homogenate. Dense canopies at the Morgenster vineyard over the three seasons lead to lower total anthocyanin and quercetin-3-glucuronide concentrations compared to the Anhöhe and Plaisir de Merle vineyards. The shading of bunches by the dense canopy most likely contributed to this. Catechin, epicatechin, proanthocyanidin and polymeric phenol concentrations decreased significantly from veraison until harvest. Seasonal differences were noted in the four vineyards. No correlations could be found between the general wine quality and the phenolic compounds, but a weak trend was observed for total anthocyanins in the homogenate. A trend was found with the total flavan-3-ol to anthocyanin ratio determined by RP-HPLC analysis of the grape homogenates (r = 0.40, p = 0.00). This ratio varied between 1 and 3 for the wines rated as being the best quality. Phenols by themselves do not give a clear indication of optimal harvest time. From this study it appears that no single parameter could consistently indicate optimal ripeness over the seasons or per vineyard, but the maximum berry colour (anthocyanin concentration) did give an indication of optimal harvesting time. It is clear that a combination of parameters could predict the optimal time more precisely as with the above mentioned model but more research is needed to this end.