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Cultivation of Pinotage in different climatic regions (Part 2):
The influence of canopy management, vine frame and cordon height on the viticultural and oenological performance of Pinotage in climate region 2
Danie van Schalkwyk & André Schmidt, ARC Infruitec-Nietvoorbij, Stellenbosch
Key words: Climate, canopy management, vine development, wine quality.
INTRODUCTION
The purpose of the study was explained in detail in a previous article "Cultivation of Pinotage in different climate regions (Part 1)" in Wynboer (Van Schalkwyk & Schmidt, February 2009). In short, the aim of the study was to determine whether climate region, bush vine compared to trellising and optimal canopy management compared to minimum canopy management have a significant influence on Pinotage wine quality. This article only discusses the results obtained by the investigation in climate region 2.
TRIAL PROCEDURE
The trial procedure was discussed in full in the first article in the series and in short, it entailed the following:
Seven trial sites each were laid out in existing young (1 to 2 year old) Pinotage vineyards at different producers in climatic regions 2, 3 and 4. For statistical purposes each producer site was considered a repetition and the treatments were applied in a randomised manner. The sites were selected based on macro-climatic data according to Average February Temperature (AFT), viz. climate region 2 (19 - 21°C), climate region 3 (21 - 23°C) and climate region 4 (23 - 25°C). Climate region 2 had trial sites in Darling, Stellenbosch, Somerset West and the Hermanus vicinity.
Pinotage vines from the same clone (PI 48) were used and developed according to four vine development methods, namely: bush vine with 20 cm trunk length, bush vine with 30 cm trunk length, split cordon with 30 cm trunk length on Extended Perold (EP) and split cordon with 60 cm trunk length on Extended Perold. Normal recommended vine development (green shoot in the case of split cordon) took place, and bearer spacing entailed 12.5 cm between bearers = 10 two-bud spurs per vine for split cordon and 5 two-bud spurs in cup form for bush vines.
Two randomised canopy management treatments were applied, 1) minimum canopy management (MC) where suckering took place between the bearers only, with all bearer shoots left in place and no leaves removed, 2) optimal canopy management (OC) where suckering took place between the bearers and two shoots only were left per bearer, and leaves removed where necessary.
Grapes from each treatment were harvested at approximately 25°B ripeness and experimental wines made from 2003 onwards in Nietvoorbij’s experimental cellar according to the experimental method for red wines. Each season’s wine quality and maturation potential were judged 6 and 24 months after bottling according to standard organoleptic procedures by a trained judging panel using the 10-point line scale method.
RESULTS AND DISCUSSION
Canopy density
The average canopy characteristics of the various treatments are indicated in Table 1. Higher scores for canopy characteristics and lower scores for the total canopy density indicate better canopy and probably improved micro-climatic conditions. Significant differences in canopy characteristics and density occurred among the treatments, thereby raising expectations that differences in wine quality would occur. The application of optimal canopy management practices (OC) significantly improved the total canopy characteristics and density as regards the trellised treatments. Significantly fewer shaded leaves were present where OC was applied. With OC, a bigger percentage leaf loss occurred during heatwaves resulting in more sunburn damage for this treatment compared to the MC treatments. Denser canopies following the application of MC can be beneficial in extremely hot conditions as more leaves remains after leaf loss to protect the bunches against direct exposure to the sun.
Click image below to view Tables 1-6:
Sunlight penetration measured inside the canopy of the treatments to quantify the photosynthetic active radiation inside the different canopies, indicated that due to the OC treatments having less dense canopies, these treatments received better sunlight penetration which could have promoted photosynthesis inside these canopies (data not shown). The open cup shape of the bush vine treatments improved sunlight penetration.
Viticultural performance
The application of OC did not accelerate ripening as had been expected (Table 2a). Sugar accumulated more slowly in the trellised treatments due to the heavier crop and the grapes reached the same ripeness as the bush vine treatments only between 8 and 12 days later. The general physical condition of the grapes from all the treatments was good during the harvest (data not shown).
Production
The optimal canopy management treatments produced fewer bunches as a result of heavy suckering and contributed to the fact that all MC treatments had higher yields (Table 2a). The average yields across the seasons were relatively low, especially in the bush vines where serious wind and foraging damage occurred at some of the sites. Porcupines and wild buck were responsible for a fairly high percentage of foraging damage at some of the bush vine sites and had a detrimental effect on yields. For example, in 2003 yields of the 30 cm OC bush vine treatments differed from 1.4 t/ha to 18.2 t/ha among trial sites. Yields also differed from one season to the next and the highest average yields occurred in 2003. Although the average yields were relatively low, one of the 60 cm MC trellis treatments at one of the trial sites produced a yield of 23.7 t/ha in both the 2004 and 2005 harvest seasons.
The lower yields of the OC vine development treatments did not cause the average bunch mass, berry mass and volumes in these treatments to increase significantly (Table 2a). Significant differences in bunch and berry mass and berry volume were measured in some seasons, but no pattern could be discerned. The OC treatments did not always realise higher values.
During the study an attempt was made to harvest at the same sugar content (25°B) at all the sites, consequently there were few significant differences in the average must analyses (Table 2a). The application of different canopy management practices did not have a significant influence on the must composition of a specific vine development treatment either. Significant differences did, however, occur among the various treatment combinations. Skin colour concentrations tended to be higher with the application of MC treatments for all vine development treatments, except for 20 cm bush vines. On average MC 60 cm trellis produced the highest skin colour concentration.
As could be expected the bush vines with fewer spurs per vine produced significantly lower yields than the trellis treatments (Table 2b). If the perception is true that low yields generally produce better wine quality, one would therefore expect the bush vines to produce better quality wines. The 20 cm bush vine and 60 cm trellis treatments yielded the smallest and the biggest bunches respectively. Wind and foraging damage that occurred in some seasons also had a detrimental impact on the yields of the bush vines and at some sites resulted in very low bunch and crop yields. Better total acid concentrations were obtained with the 20 cm bush vines, while the 30 cm trellis resulted in the lowest total acid concentrations. Although no significant differences in skin colour occurred, it seems as though skin colour concentrations tended to be slightly 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).
As a result of fewer bunches in all the vine development treatments, optimal canopy management produced significantly lower yields than MC (data not shown). Otherwise there were no significant differences in the average bunch characteristics and must analyses.
The study clearly showed that yields, bunch mass, berry mass, berry volume and shoot mass differed considerably on the various farms and this can probably be ascribed to differences in soil and site (terroir).
Wine analyses
In climate region 2 treatment combinations regarding canopy density and vine development had a significant influence on the average alcohol per volume, total acid and pH of Pinotage wines (Table 3a). Optimal canopy management induced lower pH in most vine development treatments. The only significant difference occurred among the pHs of the MC 20 cm bush vine and OC 30 cm trellis. In contrast with the observation that the analytical skin colour intensity of the MC treatments tended to be higher, the opposite as regards wine colour was observed in most vine development treatments. Although not significant, the total phenolic concentrations tended to be higher with MC in all vine development treatments, except for the 20 cm bush vines. In the course of the study no proof could be found that OC improved the wine composition of the various vine development treatments in any one season or on average over several seasons.
A comparison of the average wine analyses for the various vine development treatments indicated that vine development had hardly any significant influence on the chemical wine composition of Pinotage wines in climate region 2, measured against the average of the seasons or within seasons (Table 3b). It seems though that the analytical wine colour concentration of the bush vines tended to be higher than that of the trellis treatments. Total phenolic concentrations showed an inverse trend.
Wine aroma and wine quality
Experimental wines were subject to sensorial evaluation for aroma intensity and quality annually 6 and 24 months after bottling. Results for the six-month-old Pinotage wines indicated that although OC significantly improved the sensorial wine colour of 30 cm bush vines in 2003 and 30 cm trellis in 2005 and 2006, it did not have a significant influence on the wine quality of these treatments (Table 4). The only wine quality differences were observed in 2005 wines where 30 cm bush vine OC produced the best and 30 cm trellis MC the poorest quality wine.
When comparing the average sensorial wine colour and quality with the averages for the different vine development treatments, it is evident that the 30 cm bush vines had a significantly higher colour intensity in 2003 and 2005, and 20 cm bush vines in 2004 (Table 5). The only significant difference in average wine quality occurred in 2006 when the 20 cm bush vine treatment produced higher quality wines than the 30 cm bush vine treatment. The averages over the seasons indicated that there were hardly any differences in sensorial wine colour or wine quality.
A comparison between the sensorial evaluation results of 6 and 24 month old wines indicated that the differences in colour and aroma concentrations between vine development treatments that occurred in the young wines disappeared with maturation (Table 6). There was, however, a change in the intensity of the different aromas, be it an increase or decrease in intensity.
Although average wine quality was significantly influenced by vine development or canopy management, the treatments had a considerable influence on the intensity of aromas across all seasons (Fig. 1). It was also clear that seasonal climatic differences influenced the aroma profile and aroma concentrations of Pinotage. Wines from the 2003, 2004 and 2007 seasons had a more prominent berry character and the intensity thereof was also more concentrated than that of the other aromas.
Click image below to view Figures 1-3:
Correlation between wine colour, production and wine quality
Grapes from the OC treatments on all the trial sites were evaluated for four consecutive seasons to determine the relationship between analytical skin colour and wine quality. This investigation indicated that there was a fairly good correlation between Pinotage skin colour and wine colour in some seasons (Marais et al., 2001; Marais & October, 2005). In an attempt to confirm that sensorially observed wine colour also correlated with wine quality, the relationship between wine colour and wine quality was investigated. It was found that sensorial wine colour is not necessarily a good measure to predict wine quality (Fig. 2).
Although several research projects have shown that production/ha per se does not have a significant influence on wine quality, the tendency remains to manipulate vines to produce lower yields to induce so-called higher wine quality (Van Schalkwyk et al., 1995; Van Schalkwyk et al., 1999). If the perception of lower yields holds true, one could theoretically expect the bush vines that had been pruned to an average of 10 bud spurs per vine, compared to the 16 bud spurs per running metre of the trellis treatments, to produce better wine quality as a result of their lower yields. A comparison between yield and average wine quality showed, however, that the perception of "low yields, high wine quality" cannot be supported by this study (Fig. 3).
CONCLUSIONS AND RECOMMENDATIONS
The greater density canopies of vines that have not been optimally suckered, may be beneficial during extreme heat conditions in dryland and supplementary irrigation vines since there is more foliage to protect the grapes against sunburn.
January temperatures are a better norm for the division of Pinotage cultivation areas into climate regions because most Pinotage sites reach optimal ripeness from the middle of January and are harvested at the beginning/middle of February.
There was no conclusive evidence that optimal canopy management or different vine development treatments had a significant influence on the average wine quality of Pinotage in climate region 2. However, significant differences did occur at farm level during some seasons. Although one cannot make a general recommendation regarding canopy management or vine development for climate region 2, there are instances where bush vine or trellising can be recommended at farm level. Some farms have already adjusted new plantings accordingly. The study also showed that some trial sites produced better quality wines than others due to having more beneficial terroir.
For more information contact Danie van Schalkwyk at ARC Infruitec-Nietvoorbij, e-mail vschalkwykd@arc.agric.za.
REFERENCES
Marais, J., Iland, P. & Swart, E., 2001. Exploring the relationship between Pinotage grape colour and wine quality - Preliminary results. Wynboer 139, 76 - 78.
ABSTRACT
Long periods of extreme temperatures above 35°C occurred during January and February for the duration of the project (2003 - 2006). These hot conditions resulted in excessive loss of leaves at some of the plots and sunburn of the exposed grapes in climate region 2. In some plots grapes of the minimum canopy management treatments were less subjected to sunburn during the hot periods, as more leaves were present to protect bunches.
The larger number of shoots left on the bearer spurs of the minimum canopy management treatments induced more bunches per vine and thus higher yields. Irrespective of the plant width within rows bush vines were pruned with five two-bud spurs while the trellised vines were pruned with ten two-bud spurs per vine with the result that trellised vines had more bearers per vine and produced more bunches and thus significantly higher yields. Significant bunch-, berry mass and berry volume differences occurred to a lesser extent. Irrespective the differences in yield etc., no significant differences occurred in the overall wine quality of six or 24 month bottle matured wines of bush or trellised Pinotage, indicating no preferences for either vine structure. Optimal canopy management improved the canopy and density and thus micro-climate conditions within the canopies of the different vine structure (bush vine and trellis) treatments but did not improve the wine composition and quality. It was, however, found that an increase in cordon height tended to improved wine colour in climate region 2. Phenol concentrations tended to be higher with an increase in cordon height and trellising. Sensorial evaluation for aroma and wine quality proved that many differences in wine styles were evident and identifiable with specific plots.
Although no broad recommendation concerning the preferred vine structure can be made for climate region 2, significant differences in the wine quality of these vine structures were found at farm level, proving that terroir is important when deciding to establish bush or trellised Pinotage.
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