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Cultivation of Pinotage in various climatic regions (Part 3):
The impact of canopy management, vine frame and cordon height on the viticultural and oenological performance of Pinotage in climate region 3
Danie van Schalkwyk & André Schmidt, ARC Infruitec-Nietvoorbij, Stellenbosch
Key words: Climate, vine development, wine quality.
INTRODUCTION
The objective of the investigation was explained in detail in the previous article "Cultivation of Pinotage in various climatic regions (Part 1)" in Wynboer (Van Schalkwyk & Schmidt, 2009a). In short, the investigation aimed to determine 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 3.
TRIAL PROCEDURE
The trial procedure was explained in detail in the first article of the series; in short it entailed the following:
Six trial sites were laid out in existing young (1 to 2 year old) Pinotage vineyards at different producers in climate region 3. Each producer site was considered a replication and the treatments were applied randomly. The sites were selected based on macro-climatic data according to Average February Temperature (AFT) (climate region 3: 21° - 23°C). The trial sites were situated in Stellenbosch and Kuils River.
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), 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 only took place between the bearers 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, leaves were also removed where applicable.
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). Several significant differences in canopy characteristics and density were observed, consequently differences in the wine quality of the different treatments could be expected (Table 1a). Canopy characteristics and density of both trellis treatments were significantly improved by the application of optimal canopy management practices (OC). 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.
The average canopy characteristics of the 60 cm trellis treatment were significantly better than those of the low 20 cm bush vines (Table 1b). No significant differences between the trellis treatments occurred in the average canopy densities (30 cm and 60 cm).
The total effect of OC on all the vine development treatments showed that canopy characteristics and canopy density improved significantly (Table 1c). The significantly lower percentage shadow leaves and bunches occurring in these treatments indicated that the canopies were not as dense as those of the MC treatments.
Click image below to view Tables 1-6:
Sunlight penetration measured inside the canopies of the treatments in order to quantify the photosynthetic active radiation inside the various canopies, indicated that the canopies of the OC treatments which were less dense improved sunlight penetration (data not shown). Photosynthetic activities inside these canopies were consequently improved and therefore higher quality wines could be expected.
Viticultural performance
Ripening was not advanced in climate region 3 by the application of OC (Table 2a). Sugar accumulation in grapes from the trellis treatments was slower with the result that some of these treatment combinations achieved the same ripeness as that of certain bush vine combinations 5 to 11 days later. Evaluation of the grapes’ general physical condition during the harvest showed that a higher percentage of damage from eating by buck and porcupines as well as sunburn occurred in the bush vines (data not shown).
Yield
No significant differences in the yield of the OC and MC were measured in the various vine development treatments, although those of the OC tended to be lower (Table 2a). However, optimal canopy management resulted in fewer bunches in all the vine development treatments as a result of more stringent suckering. Yields differed from 3.2 t/ha in 2005 to 32.7 t/ha in 2003 in 30 cm trellis. This trend caused the average yield across the seasons to be relatively low. Gale force wind during some seasons impacted so negatively on the yields of bush vines that some 20 cm bush vines yielded as little as 0.4 t/ha in 2006.
Optimal canopy management resulted in a significant increase in bunch mass in the 30 cm bush vines and trellis only (Table 2a). Although the average berry mass and volume were not significantly affected, considerable differences did occur in some seasons. The greater number of shoots that occurred due to MC in the various vine development treatments, resulted in increased shoot mass in all instances except the 30 cm bush vines (data not shown). Significant differences in the sugar, acid, pH and skin colour of the treatment combinations occurred, but not among the canopy management treatments of the various vine development treatments. The skin colour concentration of the minimum canopy management tended to be higher in most of the treatments, probably due to the higher percentage bunch exposure.
As expected, the two trellis treatments, due to the greater number of bearers and therefore bunches, resulted in significantly higher yields on average than the bush vines (Table 2b). The 60 cm trellis treatment yielded the heaviest bunches; a split cordon of 60 cm therefore seems to promote bunch mass in climate region 3. Due to the fact that the berry mass did not show the same trend, the higher bunch mass can probably be ascribed to improved berry set. Although no significant differences in skin colour occurred, it seems as though skin colour tended to be higher with an increase in cordon height (30 cm bush vine compared to 20 cm bush vine and 60 cm trellis compared to 30 cm trellis).
The smaller number of bunches of the OC treatments in general caused the OC’s average yield across all the vine development treatments to be significantly lower than that of the MC (data not shown). Otherwise no significant differences occurred in the average bunch characteristics and must analyses.
Yields, bunch and berry characteristics and shoot masses differed considerably among the different farms as in the case of climate region 2 (Van Schalkwyk & Schmidt, 2009a). This is probably mainly due to the differences in soil and location (terroir).
Wine analyses
As in climate region 2 the treatment combinations of canopy density and vine development impacted significantly on the extract, total acid, pH, etc of Pinotage wines in climate region 3 (Table 3a). However, no significant differences occurred among the canopy treatments of specific vine development treatments. In the study, OC yielded the most intense wine colour in the 20 cm bush vines and MC in the 60 cm trellis the least intense wine colour. OC seems to promote wine colour to a slight degree. Although minimum canopy management of the 60 cm trellis resulted in the poorest wine colour, it produced the highest total phenol concentration and OC 30 cm bush vines, the lowest. It was not, however, possible to prove that OC or MC consistently increased or reduced the total phenol concentrations of Pinotage.
A comparison of the average wine analyses for the various vine development treatments showed that 20 cm bush vines in climate region 3 produced the highest and 60 cm trellis the lowest extract concentration (Table 3b). The two bush vine treatments produced wines with a significantly higher total acid concentration, while the 20 cm bush vines had the best wine colour on average. Although not significant, it is clear that the total phenol concentration of the two trellis wines tended to be higher. The same trends with regard to wine colour and phenol concentration were observed in climate region 2 (Van Schalkwyk & Schmidt, 2009b).
Wine aroma and wine quality
Experimental wines were evaluated sensorially for aroma intensity and quality 6 and 24 months after bottling. The only significant differences in the wine colour and quality of OC and MC wines occurred in the 30 cm trellis treatment, in 2006 and 2003 respectively when MC produced significantly better wine colour and quality wines than OC (Table 4 & Fig. 1). No proof could be found, however, that a specific treatment combination consistently produced the best wine colour or quality. Significant differences occurred from one season to the next. It is obvious, however, that the wine colour of the two trellis treatments was significantly lower most seasons, especially that of the 60 cm trellis (Table 5). Most seasons the 20 cm bush vine treatment had the best wine colour. Considerable variation in wine quality position occurred over the various seasons, but it does seem as though bush vines generally produced better wine quality. As with the study in climate region 2 these trends are so marginal that there is no concrete proof that any of the treatments should be recommended over another (Van Schalkwyk & Schmidt, 2009b). Sensorial evaluation of 24 month old 2003 and 2004 Pinotage wines also showed that the trends with regard to sensorial wine colour and wine quality remained unchanged during bottle ageing (Table 6).
From Figure 1 it is clear that seasons impacted greatly on the aroma intensity of Pinotage. Climatic conditions in 2003, 2004 and 2007 were generally more conducive to berry character, whereas a plum character was more prominent in 2007 and cherry in 2006. The application of the various canopy management treatments within seasons also had a significant impact on the intensity of various aromas.
As with the study in climate region 2, a comparison of the sensorial evaluation results of 6 and 24 month old 2004 Pinotage wines showed that the differences in colour and aroma concentrations in the young wines from different vine development treatments disappeared with maturation (Table 6). The prominence of the various aromas changed, either increasing or decreasing in intensity. Corresponding results were obtained with the 2003 wines.
When comparing the average wine results of the canopy management treatments, there is, as in climate region 2, no proof that optimal canopy management under the given trial conditions improved the wine quality of Pinotage in climate region 3 (data not shown).
Correlation between wine colour, yield and wine quality
In an attempt to confirm that sensorially observed wine colour also correlated with wine quality, the relationship between sensorial wine colour and wine quality in the wines from climate region 3 was also investigated. The latter comparison showed that perceptible wine colour in climate region 3 did not give a good indication of anticipated wine quality (Fig. 2).
Click image below to view Figures 1-3:
The perception that yield influenced wine quality was also tested in climate region 3 and once again, as in the case of climate region 2 and results from several previous research projects (Van Schalkwyk et al., 1995; Van Schalkwyk et al., 1999; Van Schalkwyk & Schmidt, 2009b), it was found that yield/ha per se did not impact on wine quality (Fig. 3).
CONCLUSIONS AND RECOMMENDATIONS
Although the application of optimal canopy management practices improved canopy density and probably also the micro-climatic conditions inside the canopy of the various trellis treatments, it did not improve the wine quality of Pinotage. The cost of applying optimal canopy management should therefore be taken into account before applying this practice. Denser canopies may be beneficial during prolonged heat-waves seeing that more leaves are present to protect bunches against sunburn under these conditions. Optimal canopy management should not be applied to bush vines in areas where strong wind prevails regularly.
Trellising, be it 30 cm or 60 cm, not only improved the Pinotage yield in climate region 3, it also improved skin colour. Although the same trend did not occur with regard to wine colour, the total phenol concentrations tended to be higher. This investigation could not find any proof that bush vine Pinotage in climate region 3 yielded better quality wines than trellised Pinotage. In view thereof, it is recommended that it is more profitable to cultivate trellised Pinotage in climate region 3. It has been found, however, that bush vines or trellising yielded significantly better wine quality on some farms in some seasons and recommendations may therefore differ among farms.
The perception that high yields per se produced lower quality Pinotage wines, was once again proved wrong. High yield Pinotage vineyards where the growth/yield ratio was balanced and sufficient shoot growth occurred, had the potential to produce high quality wines in climate region 3.
ACKNOWLEDGEMENT
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.
Hunter, J.J., 1999. Present status and prospects of wine grape viticulture in South Africa. Proc. 11th Meeting study group for vine training systems. June 1999, Marsala, Sicily, Italy, 70 - 85.
Van Schalkwyk, D., Hunter, J.J. & Venter, J.J., 1995. Effect of bunch removal on grape composition and wine quality of Vitis vinifera L, cv. Chardonnay. S.A. J. Enol. Vitic. 19, .15 - 25.
Van Schalkwyk, D., De Villiers, F.E. & De Villiers, F.S., 1999. Die invloed van produksienorme op die wyngehalte van wyndruifkultivars in die Robertson omgewing: Ruby Cabernet. Wynboer Tegnies 123, 8 - 12.
Van Schalkwyk, D. & Schmidt, A., 2009a. Verbouing van Pinotage in verskillende klimaatstreke (Deel 1): Klimaatsverskille. Wynboer 234, 10 - 14.
Van Schalkwyk, D. & Schmidt, A., 2009b. Verbouing van Pinotage in verskillende klimaatstreke (Deel 2): Die invloed van lowerbestuur, stokraamwerk en kordonhoogte op die wingerd en wynkundige prestasie van Pinotage in klimaatstreek 2. Wynboer 235, 17 - 23.
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