AS DVO 05
Optimising productivity in vineyards and potential effects on grape and wine composition for a specific production goal.
Strever, A E
Stellenbosch University. Department of Viticulture and Oenology
Strever, A E
Deloire, A J
Du Toit, W J
Adams, L F
The main objective of this project is to study optimisation of vineyard yield and product quality through modified grapevine balance and microclimate by studying some underlying factors that need to be taken into account when adapting training/trellising and/or pruning systems under different vigour conditions. In the current economic context, wine grape producers are under great pressure to maximise yield while maintaining a certain quality aimed at a specific production goal and price point. There may be many causes for vineyards that function sub-optimally; one of the aspects that add to this problem is the perception that only low yielding vineyards are able to produce high quality grapes, which in many cases also lead to excessive crop control practices. It is not often debated how larger or more vigorous grapevines that are in physiological balance can be managed to produce higher yields of high quality suitable for ultra-premium/icon wines.
In this study four different trellis/training systems (double split-cordon gable, vertical shoot positioning, sprawling and a ballerina or double Smart-Dyson system) were established in a trial layout. The trial was located in a Vitis vinifera cv. Shiraz vineyard in Stellenbosch, and some trellis/training modifications were also additionally studied in an industry case study. Basically productivity and grape- and wine composition were altered as a result of differing canopy microclimate, grapevine balance regimes and yield component compensation reactions. There were two different sprawling training systems (double and standard bud load) which were combined in the second season and subjected to a lighter pruning – namely “simulated mechanical pruning” (box pruning by hand). Pruning and harvest data were collected over two growth seasons from each grapevine in the plot. The large number of single-vine replicates made it possible to determine main yield components in a large part of the study. Shoot growth, shoot characteristics (leaf area, lateral number, internode length), canopy microclimate, physiological measurements, water status and ripening evolution were recorded for some of the treatments to establish trends between grapevine balance and associated compensation reactions. Qualitative descriptive analysis was performed on the wines produced from treatments for selected seasons.
In general, the industry case studies highlighted the difficulties related to training system conversion in a practical setting, as well as observed mismatching between the applied system and the existing vigour and yield in the converted vineyards. Generally (as in the field trial) the converted vineyards were not irrigated or fertilised differently – and our results showed how this negatively impacted over seasons.
Results from canopy microclimate as well as soil and plant water status measurements accentuated external effects on the grapevine’s adaptation to microclimate. Bud load increase led to the obvious differences in shoot and cane numbers, as well as differential effects on yield components (bunch numbers, fertility, budburst percentages) which also impacted on grapevine water status as well as fruit development and ripening. It also seemed that seasonal climate, soil and plant water status effects and microclimate can interact to either accentuate or diminish effects of trellis/training system adaptation.
The treatments (considering that all were performed in an existing vineyard) needed time for adaptation in order to find a “new balance”, which was evident in especially the first season of both trials. 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 2012/13 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 2012/13 season was the number of bunches produced per shoot (fertility), while increased budburst percentage and bunch mass in the 2013/14 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 2013/14 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 2013/14 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.
The SD treatments had higher yield:pruning mass ratios, but not initially due to higher yields, but more due to reduced vigour. This reduced vigour did not seem to favour ripening, as it seemed to coincide to high water demands from the more exposed canopy. The SD and sprawl treatments showed large increase in yield, mostly due to bud load and bunch number increase, but from the 2013/14 season’s results this does not seem to be sustainable. Despite higher vigour of other treatments in this season, the vigour of the SD and especially the sprawling treatments did not increase – suggesting issues with reserve status early season.
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.
Wine sensory results did not show large differences for the SD treatments, and it was not evident that the higher yield caused any negative effects.
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.
It is clear that trellis/training system conversion has to be done in conjunction with careful planning and execution of short term practices such as irrigation and fertiliser application. In these trials, we did not adapt these two aspects separately in the modified systems, with the goal to show its impact on the grapevine’s long-term sustainability. We showed so far that bud load can be significantly increased, even in lower vigour grapevines, without clear negative effects on grape composition or wine attributes, but rather changes in wine style for Shiraz.
Strever, A E. 2012. Training systems, plant spacing and plant water use. Presentation at the South African Society for Enology and Viticulture Winter Forum, 20 July, Stellenbosch, South Africa.
Strever, A E. 2012. Water use of training systems. Presentation to Distell. 17 August, Stellenbosch, South Africa
Bosman, A and Strever, A E. 2012. The impact of modifying grapevine balance by trellis system conversion on yield components of a grapevine. Paper presented at the 34th National Congress of the South African Society for Enology and Viticulture. 14-16 November, Somerset West, South Africa.
Bosman, A and Strever, A E. 2013. Modification of vine balance and the influence thereof on various yield components. Presentation to the Western Cape Viticulture Group. 17 May.
Strever, A E. 2014. Training system conversion, some preliminary thoughts. Presentation at the South African Society for Enology and Viticulture Forum, April, Stellenbosch, South Africa.
Strever, A E. 2014. Training system conversion, some preliminary thoughts. Presentation at the VinPro Information Day, 21 May, Rawsonville, South Africa.
Bosman, A, 2014. The impact of modifying grapevine balance by trellis system conversion on yield components of a grapevine. SASEV forum day, April 2014.
Davel, A. 2015. Optimizing productivity in vineyards and potential effects on grape and wine composition with a specific production goal. MSc AgricSciences. University of Stellenbosch, Stellenbosch.
Rabie, PA. 2015. A simulation model for evaluating the long-term financial impact of different wine grape production systems. MScAgric thesis, Stellenbosch University.
Du Toit, WJ 2016. WW WdT 12/02 – “Investigating the leaf to fruit ratio (source-sink) and bunch microclimate (training system x canopy manipulation”). Winetech Final report.