Browsing by Author "Bosman, Anneli"

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    Optimising productivity and grape composition (grapevine potential) for a specific wine production goal: adaptation of grapevine reproductive/vegetative balance in modified training systems
    (Stellenbosch : Stellenbosch University, 2020-12) Bosman, Anneli; Strever, A. E.; Stellenbosch University. Faculty of AgriSciences. Dept. of Viticulture and Oenology.
    ENGLISH ABSTRACT: Provided the current economic context in South Africa, grape producers are being forced to think outside the box and explore and employ new approaches in order to optimize productivity in a sustainable way. Optimum productivity is only achievable once a balanced vine is capable of producing its maximum yield at optimum quality, while keeping input costs (i.e. labour) at a minimum. The perception that only low yielding, small vines are capable of producing quality yields contributes to the general reluctance among producers to consider taking actions such as converting existing trellising or training systems to increase vigour and yield. Three training systems (Smart-Dyson, vertically shoot positioned system (VSP) and a reduced canopy treatment), executed in a Vitis vinifera L. cv. Shiraz vineyard located in Stellenbosch were evaluated over the course of three seasons. The purpose was to investigate whether or not the conversion of an existing training system is indeed a viable option to increase productivity in a sustainable way and without negatively impacting on wine quality. In addition to this, the concepts of grapevine balance and compensation were studied to reach scientifically valid conclusions regarding the vine’s compensatory reaction to an alteration in its architecture. This investigation was conducted by converting an existing training system to determine whether it is possible for grapevines to reach maximum productivity (yield) without forfeiting quality. The trial vineyard was characterized by high variability in vigour. After assessing vigour according to historical pruning data, grapevines were divided into high and low vigour categories after which conversion to the altered training systems (treatments) were carried out. The layout of this experiment was a completely randomized block design. Plant and soil water status was monitored, but soil water monitoring was not measured treatment specific, which meant that the exact water requirement on a per treatment basis could not accurately be determined. Vegetative and reproductive measurements were conducted over all three seasons. Pruning and yield data was collected and the yield:pruning mass ratios were determined and compared between the various treatments. Vegetative measurements included primary shoot growth tempo and length, total lateral shoot length, total primary leaf area, total lateral leaf area and total leaf area per vine. In general, a progressive increase in vegetative growth was observed in all treatments as the trial progressed. All the Smart-Dyson treatments displayed a steady increase in yield over the course of the trial. Starting before véraison, berry sampling took place weekly and berry composition was analysed in order to determine ripening progression. Wines from each individual treatment of each season’s harvest were prepared, and the wines made during the first two seasons evaluated by means of qualitative descriptive analysis (QDA). Results obtained from QDA, indicated that no negative parameters were associated with any treatments, thus the conversion effect and increase in vegetative growth and yield had no substantial influence on composition. Instead, all indications were that wine style rather than wine quality was influenced. It was concluded that seasonal effects played a substantial role in the difference in wine styles between seasons. The conversion effect itself played a relatively smaller role when considering that no significant differences in wine attributes between treatments and controls were detected. The decision to modify existing training systems to accommodate larger vigour and increased production is an option that can be seriously considered, since this trial has proven that actions that increase yield do not necessarily mean that quality has to be forfeited.