Optimising productivity in vineyards and potential effects on grape and wine composition for a specific production goal

[摘要] ENGLISH ABSTRACT: In this study three trellis/training systems (double split cordon gable, vertical shoot positioning and sprawling systems) located in a Vitis vinifera cv. Shiraz vineyard in Stellenbosch were investigated to determine how grapevine productivity and grape- and wine composition can be altered as a result of differing canopy microclimate, grapevine balance regimes and yield component compensation reactions. Two sprawling training systems (double and standard bud load in relation to the vertically shoot positioned system) were combined in the second season and subjected to a lighter pruning, simulating mechanical pruning. Pruning and harvest data were collected over two growth seasons from each grapevine in the plot, which also displayed within-treatment and vineyard vigour-, yield- and grapevine balance variability. The large number of single-vine replicates made it possible to determine main yield components, such as bud load, budburst percentage, fruitfulness, bunch- and berry size as well as berries per bunch, and to investigate some primary components responsible for grapevine productivity. Shoot growth, shoot characteristics (leaf area, lateral number, internode length, and leaf age), canopy microclimate, physiological measurements, water status and ripening evolution were recorded to establish trends between grapevine balance and associated compensation reactions. Qualitative descriptive analysis was performed on the wines produced from each treatment in the second season.Increased bud load led to increased shoot numbers and yield, but with decreased bunch mass and grapevine vigour, in terms of total cane- and mean mass per cane and shoot length. The gable trellis system produced the highest yield between treatments in both seasons, but due to trellis conversion completion in the first season, low vigour was present. For this reason, imbalanced grapevine conditions occurred in terms of high yield to cane mass ratios (Y/CM) and low leaf area to yield ratios (LA/Y) and consequently delayed ripening. Nevertheless, the gable trellis system seemed to reach maximum productivity, as the yield between seasons remained relatively similar. The main yield component responsible for yield difference in the first season was the number of bunches produced per shoot (fertility), while increased budburst percentage and bunch mass in the second season affected yield most. More shoots led to decreased fertility and increased bunch mass in this treatment, and improved growth and high yields during the second season resulted in more desirable grapevine balance, thereby not affecting ripening negatively. The two sprawling systems only differed according to shoot number, with the double sprawling system (double the amount of buds) producing twice as many shoots and consequently higher yields. Simulated mechanical pruning, in the second season, decreased grapevine vigour as expected but increased yield considerably as a result of increased fertility. However, imbalanced Y/CM ratios occurred, delayed ripening, and a highly exposed canopy bunch zone which increased the process of leaf degradation and the occurrence of water deficits. The VSP treatment produced highly vigorous grapevines together with low yields in both seasons and as a result increased canopy density and decreased Y/CM ratios.Grapevine balance, bud load and canopy density were most associated with sensory wine attributes. The intensity of fruity wine attributes increased and vegetative wine attributes decreased as bud load and Y/CM ratios increased and canopy density decreased. The sprawling treatment displayed the highest Y/CM ratio and bud load as well as the least dense canopy. Therefore the sprawling training system produced wines containing the highest fruity attributes which is generally desirable in new world Shiraz. The dense canopy as a result of vigorous growth, low Y/CM and bud load of the VSP treatment produced wines dominated by vegetal attributes. The gable treatment, which displayed Y/CM ratios, bud load and canopy densities with general values between the VSP and sprawling treatments, produced wines with vegetal and fruity attributes, with the latter probably being more dominant.Changing trellising-, training- and pruning systems clearly led to the production of different wine styles. Grapevine balance, canopy density and pruning severity should be taken into consideration when attempting to produce wines intended for specific production goals. Therefore, increased yield as a result of alternative pruning-, training- and trellising systems does not necessarily affect wine composition negatively, if not more beneficially, and should be considered as a solution regarding production profitability.

[发布机构] Stellenbosch University