Thesis (MscAgric (Viticulture and Oenology))--University of Stellenbosch, 2007. / A common phenomenon in most South African vineyards, especially in the Western
Cape region, is that of within vineyard variation. This variation phenomenon is caused
by an array of controllable and non-controllable factors that interact with each other to
affect vine vigour. Controllable factors can be managed by the grape grower, while the
non-controllable factors have to be managed in the planning process in order not to
negatively affect productivity or product quality.
The main goal of any grape grower is to optimise vine performance in an attempt to
achieve the best possible yield while at the same time allowing vines to optimally ripen
grapes towards optimal wine quality. A grape grower has to use every possible means
and technique available to him in order to manage his vineyards in such a manner as to
achieve this goal. In the past, it was difficult to visualize the extent and distribution of
vigour variation in vineyards, but with modern technological improvements in the field of
remote sensing, grape growers are able to identify and specify different vigour levels
within a vineyard.
When remote sensing is applied in a vineyard, the grape grower can identify certain
areas that may need more specific attention than others. Consequently, managerial
decisions based on detailed information can be made in an attempt to improve the
general condition and performance of a vine. Not only can the acquired information be
used to plan managerial actions throughout the season, but it can also be used to plan
and devise harvest strategies. Some areas in a vineyard may be at a certain point in the
ripening process and need to be harvested, while grapes from other areas still need to
develop the wanted flavours. One managerial action applied at véraison by some grape
growers, is that of crop thinning. Different vigour areas can now be subjected to various
crop thinning actions in an attempt to determine the best crop load for a vigour level.
With this in mind, two studies were launched to firstly investigate the interaction
between vine vigour and harvest dates; and secondly to investigate the interaction
between vine vigour and crop load and how their combined interaction might influence a
vine’s characteristics, grape composition and wine quality. Vigour variation was firstly
identified through multispectral aerial imagery, and then visually verified by visits to the
experimental vineyards. The multispectral aerial image was then “orthorectified” in order
to produce a classified multispectral image. The image was classified through different
colour codes that were assigned to the different vigour levels to clearly distinguish
between them. A series of vegetative and reproductive measurements were conducted
to try and establish if any correlations could be obtained of the interaction between vine
vigour, different harvest dates and crop loads. In order to verify differences in vine
vigour, underlying causes were also determined through soil analyses of which
chemical analysis, bulk density, porosity, as well as root penetration and distribution
were determined. Vegetative measurements that were conducted for both studies
indicated good correlations between the different vigour levels and the image
classifications. The results also identified the effect that topping (mechanical or manual) had on the main and lateral leaf areas. Reproductive measurements throughout the
season, in the form of berry sampling, showed changes in berry composition and
accentuated the effects of the different treatments, which could also be confirmed
through sensorial analysis of the wines. The results also emphasized the need to not
only make use of one of two chemical parameters to identify grape ripeness, but to
incorporate a number of parameters, such as sugar, pH and acid levels. From the
varying grape chemical characteristics, a wine style can be identified that might carry
the approval of the winemaker for the production of a specific type of wine. Soil studies
of both vineyards also gave important evidence for the causes of vigour variation.
The data collected will hopefully provide grape growers with information that will
enable them to make educated decisions concerning grape production and how vigour,
in conjunction with different harvest dates and crop loads, will enable them to produce
fruit of good quality and, so doing, improve their financial position.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/1677 |
| Date | 03 1900 |
| Creators | Quixley, Pieter C |
| Contributors | Strever, A. E., Carey, V. A., 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 | English |
| Type | Thesis |
| Rights | University of Stellenbosch |
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