In a former article (23rd April 2012), I told you a bit about our experience of vigour distribution in some Grenache vines. I’d like to recommend that you have a look at it again so that you can connect it with this one. In order to help you interpret the results, we examine several connections to better understand how the vines responded to our pruning.
Observation and discussion of results
1. Wood production
After analysing the graphs showing the data on vigour and stems, we can see there is a direct relationship between the reduction of number of stems during pruning and the increase of vigour during the vegetative cycle.
At the beginning of this experience, that is to say, in winter 2011, pruning was done taking into account the weight of the stems of a vine, i.e. taking vine vigour into account. As we can see on graph #1, the vines in the first three groups, in 2010, had too many stems left in relation to their vigour so in the following year their number was cut down. However, in group number 4, the amount of stems left was insufficient in relation to their vigour and in 2011 some more stems were left unpruned.
The response of the vines, at the end of the 2011 cycle, resulted in the first three groups increasing their vigour in comparison to 2010 and in the fourth group reducing it, as shown in graph #2.
We have also observed some variation in the weight of stems. On graph #3 we can see there is an inversely proportional relationship between the variation in the number of stems and the variation of individual weights.
The first group, with extremely short stems, has increased the length and weight of each stem the most. The second and third group follow the same trend but group 4 has reduced the weight of its stems.
All these variations are shown in the following table:
2. Grape production
Grape production per hectare has been very different in the groups due to the difference in vigour. So, production per hectare and production per vine are directly proportionalto vigour. Logically those vines with longer arms or cordons with more stems produce more grapes. See graphs 5, 6, and 2.
It is very interesting to state that, on the other hand, production per stem is roughly equal in all the groups, with only a slight difference. Graph #7
3. Stem length
In the whole plot of land, all the stems and their grape clusters were pretty similar. Remember that in the first group there were vines with productive arms of about 40 cm in length and 120 gr in vigour and in the fourth group there were vines with productive arms of 2.4 m in length and 3.800 kg in vigour. In spite of that, the stems and their grapes were morphologically very similar. They did not only look quite alike but the small difference among them is inversely proportional to vigour. On graph #8 you can see that the less vigourous vines have slightly longer stems and the most vigorous vines have them a bit shorter.
If we now relate production to foliar surface in order to see the grams of grapes in one m2 of leaf, we can see on graph #9 that there are some differences among the groups, particularly between the first group and the rest. The first group has produced a yield of 540 gr of grape per m2 of leaf, whereas the remaining three groups have produced between 700 and 800 gr.
Because the stems in the first group were longer, that means more foliar surface and therefore less yield per m2 of leaf.
This is also reflected in the wine analyses for each group. In table 10 we can see that the wine from the first group has a higher alcohol, polyphenol and tannin content.
When tasting the wines, we also found a more structured type of wine in the first group, similar wines in the second and third group and wine with less body in the fourth group.
We can see a summary of the production data in the following table:
We do not dare to jump to any final conclusions because, among some other actions, we will repeat this experience some more years so that we can check and confirm vine response to corrective pruning.
So far though we can say that:
- Doing some corrective pruning and leaving the right number of stems in relation to the vigour of each individual vine implies that the stems have a thin diametre and a length between 1.20 and 1.50 metres.
- These stems produce middle-sized grape clusters with loose berries (not compact).
- Consequently, if the vine is vigourous and accepts many stems, we will have to adap the trellis and cordon training so that we can leave the necessary number of stems.
- The use of an automatic irrigation system is indispensable to control the amount of water necessary, in a specific part of the plot of land and at the best time, monitoring the state of the vines through soil humidity sensors.
- This vigour control method can be employed for any variety but it is particularly good for vigourous varieties such as Cariñena and Grenache.
These results, nevertheless, lead to some reflection: generally speaking, does a vine, when left with less stems than before, react by increasing its vigour? And the other way round, does a vine, when left with some more stems than before, react by decreasing its vigour? …
How can all this affect grape quality, which in short is what we are interested in?
We hope we can answer all these questions with the help of some future experiences we have already set out.