Thesis (MScAgric (Viticulture and Oenology))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Grapevine water status is considered to be the most important factor limiting plant growth and
production in the Mediterranean zones. In these regions with limited summer rainfall and limited
water resources for irrigation grapevines may experience water deficits for an extended period
of time. The demand of water for agriculture is constantly increasing, and will continue to do so
due to the rise in the world population and to the effects of climate change on rainfall and
evaporative demand in these regions. The Western Cape wine region is also classified as
Mediterranean and grapevines grown in this region are often exposed to water “stress”
conditions due to high evaporative demand and low water availability in the soil.
Plant water status of grapevines may dependent on, amongst other factors, the water potential
of soil layers close to the root system, canopy size and evaporative demand. The canopy size of
a grapevine can inherently be seen as a measure of grapevine vigour, and vigour variation
among grapevines within a vineyard is a common phenomenon in the Western Cape. The
importance of the contributions from several factors causing vigour variation within vineyards is
still a subject of debate. This may be largely ascribed to the significant amount of variability in
vineyards that researchers have to deal with during viticultural studies. However, the recent
advances in remote sensing technology have established new methods to assess grapevine
vigour variability.
In the face of the recognized variation within vineyards and the importance of a sustained
grapevine water status, for wine grape productivity and -quality, it is alarming to think that a
vineyard block is generally managed as a homogeneous entity when it comes to irrigation
scheduling. What is more alarming is the assumption that grape, juice and wine quality will be
homogeneous throughout a vineyard block – even without irrigation.
With this in mind, a study was conducted to study the interaction between grapevine vigour and
grapevine water status within a commercial vineyard with variable vigour by implementing
various irrigation regimes. Vigour variation was identified through multispectral aerial imagery
and plant-based water status determinants were used to assess grapevine water status in plots
of differing vigour within the vineyard. Soil water status was also assessed, and vegetative
growth quantified to ultimately determine the variability in vigour and its possible contribution to
the variability through the water status of the plant. Reproductive growth was monitored
continually before evaluating the effect of water status and grapevine vigour on grape
composition and subsequent wine quality.
The various methods used to evaluate grapevine vigour showed good correspondence. Pruning
mass measured at the end of the season confirmed leaf area measurement (main leaves and
lateral leaves) during vegetative growth, and corresponded well, in terms of main vigour classifications with the NDVI images collected. Berry weight and volume responded to the
various classifications, with a decrease in water deficits from one classification to the next
accompanying an increase in berry weight and volume.
Analyses of the berry composition and wines showed statistically significant differences
between the classifications. This was found for sugar content per berry, total phenols, total red
pigment, malic acid, nitrogen and pH for the grape juice analyses. Wine pH and total acidity also
differed significantly. / AFRIKAANSE OPSOMMING: In die Mediterreense sones word plantwaterstatus beskou as `n hooffaktor wat groei en
produksie van `n wingerdstok negatief beinvloed. In hierdie sones kan wingerdstokke vir lang
periodes `n tekort aan water ervaar a.g.v `n tekort aan reënwater gedurende die somer en lae
beskikbaarheid van besproeingswater. Die vraag na water vir landbou is ook konstant besig om
toe te neem in dié sones en die tendens sal voorduur a.g.v die groei in die wêreldbevolking, die
effek van klimaatsveranderig op reënvalpatrone en die hoë verdampingsfaktor. Die wingerd- en
wynstreek van die Wes-Kaap word ook geklassifiseer as Mediterreens en wingerdstokke in
hierdie streek ervaar dikwels waterspanning wat deur hoë evapotranspirasie en min beskikbare
grondwater veroorsaak word.
Van die faktore wat die waterstatus van `n wingerdstok bepaal is onder andere die
waterpotensiaal van die grondlae rondom die wortelstelsel, die grootte van die
wingerdlowerraamwerk en die evapotranspirasiebehoefte. Die omvang van `n wingerdstok se
lower binne die prieel word beskou as `n aanduiding van wingerdstokgroeikrag en variasie in
groeikrag tussen wingerdstokke is `n algemene verskynsel in die Wes-Kaap. Die rangorde, wat
die effek van die verskeie faktore wat groeikragvariasie tussen wingerdstokke bepaal, word
steeds gedebatteer. Die debat kan groottendeels toegeskryf word aan die beduidende
hoeveelheid variasie tussen wingerde waarmee navorsers te doen kry in wingerdkundige
studies. Hoewel, met onlangse vordering aangaande afstandswaarnemingstegnologie is daar
nou nuwe metodes beskikbaar om wingerdgroeikrag te evalueer.
Dit is kommerwekend om te dink dat `n wyndruifwingerd normaalweg as `n homogene
eenheid bestuur word as dit kom by besproeiing. Veral met die wete dat groeikragvariasie
tussen wingerde algemeen erken en aangeteken word, en dat volhoubare waterstatus van `n
wingerdstok van kardinale belang is vir produksie en kwaliteit van wyndruiwe. Die aanname dat
wyndruiwe, die sap- en ook wynkwaliteit homogeen sal wees regdeur `n wingerdblok is egter
meer kommerwekkend.
Na aanvang van dié denke is daar `n studie geloods om die interaksie tussen
wingerdstokgroeikrag en wingerdstokwaterstatus te evalueer. Met die studie is verskeie
besproeiingsregimes aangebring binne `n kommersiële wingerd wat interne groeikragvariasie
tentoonstel. Groeikragvariasie was geïdentifiseer deur middel van multispektrale lugfotos terwyl
die wingerdstok se waterstatus geëvalueer is met behulp van plantgebaseerde metings in die
verskillende groeikragareas. Die waterstatus van die grond is geëvalueer tesame met die
vegetatiewe groei van die wingerd sodat die groeikragvariasie en die invloed van die
plantwaterstatus op die groeikrag bepaal kon word. Die reproduktiewe groei is deurlopend
gemonitor voor die effek van wingerdstokwaterstatus en wingerdstokgroeikrag op
druifsamestelling en wynkwaliteit bepaal is. Daar was `n goeie ooreenkoms tussen die verskeie metodes wat gebruik is om
wingerdgroeikrag te bepaal. Snoeimassa aan die einde van die seisoen was ooreenkomstig met
die blaaroppervakte (hooflootblare en sylootblare) wat tydens vegetatiewe groei gemeet is, en
het ook goed korreleer, met die multispektrale lugfotos se hoof groeikragklassifikasie.
Korrelgewig en -volume het reageer op die verskeie besproeiingsregimes, en daar was `n
toename in korrelgewig en -volume saam met die afname in watertekort van een regime tot `n
ander.
Daar was beduidende verskille tussen die verskeie klassifikasies t.o.v. korrelsamestelling
analise en wynevaluasie. Die suikerinhoud per korrel, totale fenole, totale rooi pigment,
appelsuur, stikstof en pH het verskil in druiwesap analises. Die pH en suur van die wyne het ook
beduidend verskil.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/4122 |
| Date | 03 1900 |
| Creators | Boshoff, Cornelis Johannes |
| Contributors | Strever, A. E., University of Stellenbosch. Faculty of Agrisciences. Dept. of Viticulture and Oenology. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 96 p. : ill. |
| Rights | University of Stellenbosch |
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