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Cultivation of Pinotage in various climatic regions (Part 4):
The impact of canopy management, vine frame and cordon height on the viticultural and oenological performance of Pinotage in climate region 4
Danie van Schalkwyk & André Schmidt, ARC Infruitec-Nietvoorbij, Stellenbosch
Key words: Climate, vine development, wine quality.
INTRODUCTION
The objective of the study was explained in detail in a previous article "Cultivation of Pinotage in various climatic regions (Part 1)" in Wynboer (Van Schalkwyk & Schmidt, 2009a). In short, the investigation was aimed at determining whether climatic region, bush vine compared to trellis and optimal canopy management compared to minimum canopy management impact significantly on Pinotage wine quality. This article discusses the results obtained in climate region 4.
TRIAL PROCEDURE
The trial procedure was explained in detail in the first article of the series; in short it entailed the following:
Seven trial sites were laid out in existing young (1 to 2 year old) Pinotage vineyards with different producers in climate region 4. The sites were selected based on macro-climatic data according to Average February Temperature (AFT) (climate region 4: 23° - 25°C). The trial sites were situated in Agter-Paarl, Darling, Riebeek-Kasteel and Wellington. Each producer site was considered a replication and the treatments were applied randomly.
Pinotage vines from the same clone (PI 48) were used and developed according to four vine development methods, namely: bush vine with 20 cm and 30 cm bush vine trunk length, split cordon with 30 cm and 60 cm trunk length on an Extended Perold. The normal recommended vine development (green shoot in the case of a split cordon) and bearer spacing [12.5 cm (8 two-bud bearers per running metre split cordon) between bearers in a split cordon and 5 - 6 two-bud bearers in goblet format for bush vine] were applied.
Two canopy management treatments were applied randomly, 1) minimum canopy management (MC) where suckering took place between the bearers only and all the shoots that sprouted on the bearers, were left in place and no leaves removed, 2) optimal canopy management (OC) where suckering took place between the bearers and only two shoots per bearer were left.
Grapes from each treatment were harvested at approximately 25°B and experimental wines made in Nietvoorbij’s experimental cellar. Each season’s wine quality and maturation potential were judged 6 and 24 months after bottling according to standard sensorial procedures by a trained judging panel according to the 10-point line scale method.
RESULTS AND DISCUSSION
Canopy density
The average canopy characteristics of the different treatments are indicated in Tables 1a to 1c. Higher scores for the canopy characteristics and lower scores for the total canopy density indicate better canopies and possibly improved micro-climatic conditions (Hunter, 1999). As with the investigations in climate regions 2 and 3 (Van Schalkwyk & Schmidt, 2009b & 2009c) OC resulted in an improvement not only in the total canopy characteristics of the 30 cm and 60 cm trellis treatments, but also in the canopy density of these two treatments (Table 1a). Canopy management probably did not have any significant impact on the average canopy characteristics of the bush vine treatments as a result of extremely strong winds that occurred at some of the sites each season. The total canopy characteristics of the bush vines were in fact significantly inferior to those of the OC trellis treatments (Table 1b). Point-quadrant measurements (Hunter, 1992) indicated that significantly more shadow leaves and bunches were present in the trellis treatments compared to where MC was applied.
Click image below to view Tables 1-5:
The average canopy characteristics of the 60 cm trellis treatment were significantly better than that of both bush vine treatments, while only 30 cm trellis was significantly better than the 30 cm bush vines (Table 1b). There were no significant differences in the average canopy densities among the various trellis treatments. The total effect of OC across all vine development treatments showed that OC significantly improved canopy characteristics and canopy density and that there were significantly fewer shade leaves and bunches than with the MC treatments (Table 1c). Sunlight penetration measured inside the canopy of the treatments in order to quantify the photosynthetic active radiation within the various canopies, indicated that the more open canopies of the OC treatments improved sunlight penetration (data not shown).
Viticultural performance
The application of OC caused slightly earlier ripening in the 60 cm trellis only (Table 2a). Evaluation of the grapes’ general physical condition during the harvest indicated that the bush vine treatments were more subject to feeding and sunburn damage and millerandage (data not shown).
Yield
Canopy management practices resulted in a significant difference in yield in the 30 cm bush vine treatment only due to the bigger difference in the number of bunches/vine (Table 2a). The MC treatment resulted in a significantly higher yield than the OC treatment. Optimum canopy management resulted in significantly fewer bunches than MC in the bush vine treatments only. Although there were several significant differences in the bunch mass or must composition of the various treatments, optimum canopy management did not result in any significant differences in this regard in the various vine development treatments.
As far as the different vine development treatments are concerned, the two bush vine treatments yielded significantly lower yields than the two trellis treatments (Table 2b). Although the average yields obtained were relatively low for this region, yields of up to 31.1 t/ha and 32.5 t/ha respectively were obtained using 60 cm and 30 cm trellis at some of the plots in the Wellington area. The 20 cm bush vine and 30 cm trellis treatments both had significantly lower berry mass and volumes than the other two treatments. The heavier yield of the 30 cm and 60 cm trellis treatments resulted in significantly lower sugars, total acids and pHs than those of the two bush vine treatments. The best skin colour extraction was obtained from 20 cm bush vines.
Wine analyses
Despite significant differences in the wine composition of the various treatment combinations, no significant differences occurred in the wine composition of OC and MC with individual vine development (Table 3a). Wine colour and total phenolic concentrations of OC tended to be higher than those of MC in most treatments. The wine colour of 20 cm bush vine tended to be highest and OC 30 cm lowest, while MC had the highest and lowest total phenols in 30 cm bush vine and 60 cm trellis.
The significantly lower alcohol and extract levels of the trellis treatments’ wines may be ascribed to the slightly lower sugars at which these treatments were harvested (Table 3b). The significantly lower total acid concentrations of these two treatments’ wines were probably due to significantly higher yields than those of the bush vines. Wine colour in both trellis treatments was significantly lower than in the bush vine treatments and although not significant, the total phenolic concentrations also tended to be lower. This is directly opposite to results obtained by the investigations in climate regions 2 and 3 (Van Schalkwyk & Schmidt, 2009b & 2009c).
Wine aroma and wine quality
Each season’s wines were evaluated for wine quality and aroma 6 and 24 months after bottling. This evaluation showed that although differences in sensorial wine colour and wine quality occurred between treatment combinations, the only significant difference between OC and MC wine quality occurred in the 20 cm bush vine during 2003 and 2004 (Table 4). Apart from these two instances it is therefore clear that optimal canopy management did not improve the wine colour or wine quality of the various vine developments. The differences that did occur, however, were also reversed in the two seasons. One cannot state categorically, however, that canopy management does not have a significant impact on Pinotage wines, as many differences occurred within seasons at farm level. There were also differences in aroma intensity. The above is an indication that it is not possible to make a general recommendation in respect of canopy management in this climate region. Differences may occur at farm level.
In four of the five seasons the wine colour of both trellis treatments was significantly less intense than with the two bush vine treatments, thereby proving that bush vines in climate region 4 generally produced better wine colour (Table 5). Wine quality did not show the same trend, however. The only significant difference in wine quality occurred in the 2006 wines when 60 cm trellis resulted in significantly better wine quality than 30 cm bush vine. On the whole across all the seasons it is therefore clear that neither canopy management nor vine development in climate region 4 had a significant influence on the overall wine quality of Pinotage. Evaluation of 24 month old wines showed that the trends with regard to sensorial wine colour and wine quality during bottle maturation were the same (data not shown). Differences in aroma intensity in the wines from the treatment combinations occurred within seasons, but not between the OC or MC of the different vine developments, unlike the results from climate regions 2 and 3 (Fig. 1). Climatic differences between seasons had a considerable impact on general aroma intensity. Wines from 2005 were more neutral, while the 2007 wines had a fairly intense berry character (especially black currant). Both bush vine treatments had a more intense cherry character in 2006 than in the other seasons and also more intense than the trellis treatments.
Click image below to view Figure 1:
Correlation between wine colour, yield and wine quality
As in the case of climate region 3, there was not a good correlation between sensorial wine colour and wine quality in the wines from climate region 4 and consequently perceptible wine colour did not give a good indication of anticipated wine quality.
The perception that wine quality may be influenced negatively by high yields could not be confirmed in climate region 4, just as in climate regions 2 and 3 (Van Schalkwyk & Schmidt, 2009b & 2009c). This confirms previous research by the author (Van Schalkwyk et al., 1995; Van Schalkwyk et al., 1999).
CONCLUSIONS AND RECOMMENDATIONS
Despite the fact that optimal canopy management practices improved canopy density and probably the micro-climatic conditions within the canopy of the various trellis treatments, it did not result in an improvement in the wine quality of Pinotage. Minimum canopy management can be useful during lengthy heat waves because more leaves will be available to protect bunches against sunburn under such conditions and may sometimes improve the quality of the wines. Optimal canopy management is not recommended in bush vine vineyards in areas where regular strong windy conditions occur, only the shoots within the crown should be removed.
There was no proof that bush vines improved wine quality compared to trellised vines. Although better wine colour and higher total phenols were obtained with bush vines, this could not justify recommendation of bush vines rather than trellised vines. Trellising yielded more than double the yield of bush vines, which makes it more profitable to trellis Pinotage in climate region 4. Based on the results obtained, the recommendation is that Pinotage in climate region 4 should be trellised. Recommendations regarding canopy management and vine development may differ because of differences in terroir at farm level. Bush vines may be considered on lean soils under dryland conditions, where growth is insufficient to justify a trellis system.
For more information contact Danie van Schalkwyk at ARC Infruitec-Nietvoorbij, email vschalkwykd@arc.agric.za.
REFERENCES
Hunter, J.J., 1992. Manipulering van lower vir optimum gehalte druiwe. Winegrape Summer Workshop, p. 1 - 22. 3 December 1992, Stellenbosch. Nietvoorbij Institute for Viticulture and Oenology.
ABSTRACT
The effect of canopy management (optimal versus minimum canopy management), vine structure (bush vine versus trellis) and the combination of these treatments on the wine quality of 6 and 24 month vintage Pinotage wines in climate region 4 were investigated on seven farms for five consecutive seasons. It was found that optimal canopy management improved canopy density and thus micro-climate within the canopy, however, as in the case with the trials in climate regions 2 and 3 no improvement in average wine quality occurred. During some seasons, however, both optimal and minimal canopy management improved wine quality significantly in some of the plots. To prevent severe damage to the foliage, optimal canopy management is not recommended in bush vine vineyards where regular strong windy conditions occur, only the shoots within the crown should be removed.
Although bush vines produced wines with a more intense colour and higher total phenols, they did not produce wines with a higher quality than the trellised vines. Trellised vines yielded more than double the yields that were obtained with bush vines, average 12.6 t/ha and 5.3 t/ha, respectively. Yields up to 32.5 t/ha were obtained with 30 cm trellised and 31.1 t/ha with 60 cm trellised at one plot during some seasons. From an economical view point it is thus recommended that Pinotage should be trellised in climate region 4. There are, however, situations such as the cultivation of Pinotage under dryland conditions and poor soils with low nutritional volumes, where bush vines rather than trellised would be justified.
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