VSP or Pergola?

Anyone who has lived through a Central Texas summer knows how important shade can be.  Would it be any different for organic life in Texas soil?

With this in mind, I've noticed that the ancient Romans and their modern decedents in Italy and Spain have traditionally grown grapes on pergolas.

Table grapes near harvest supported by a Pergola near Zaragoza, Spain 

"The pergola trellising system promoted by the Romans and still used in Italy, normally has fewer vines per hectare - with approx 1666 vines/ha in the classic pergola-trellised vineyard, compared with around 4000 vines/ha in a regular VSP.
In the pergola system, shoot-positioning is not required and canopy management is limited. The average Italian vineyard is less than 4ha in area so finding people to harvest the grapes is less of a concern, though two issues work against the pergola trellis: the position of the arms makes harvesting difficult; and the overhead design makes it difficult to use a modern tractor."

In Italy, there is something of a controversy over the benefits of moving to the northern style: "(Guyot trellis system, largely adopted in Valpolicello around 20 years ago and now believed to produce lower quality grapes than the pergola system)" 





Here is a similar description of the controversy, but in Argentina, at similar latitudes to Texas.
"The soils throughout Argentina were developed by alluvial action and vary between sandy with some clay and gravel and limestone. Soils in the Río Negro and Neuquén (Patagonia) regions are more chalky. Some areas languish in traditional support systems where grapes are grown on pergolas (“parral cuyano”), where vines are trained high off the ground with the clusters allowed to hang down. This style was conducive to the high-yielding Criollas varieties that were the backbone of the bulk wine-producing industry that sprang up in response to the large domestic market. In the late 20th century, as the market turned to focus more on premium wine production, more producers switched back to the traditional bilateral cordon and many adopted the vertical shoot position system. In the 1970s, yields were reported as surpassing 20 tons per acre in sharp contrast to the average yields in premium wine regions such as Bordeaux and Napa Valley of 2 to 5 tons an acre. Today vineyards are managed to produce quality fruit with improvements in irrigation strategies, yield control, canopy management, and the construction of more wine-making facilities closer to the vineyards."

Here is another webpage on the subject:
"As far as vine training is concerned they have had VSP (vertical shoot positioning) since 1982 but they also have the more traditional pergola system for some vineyards, and for some of the best ones too!
 The belief that the traditional pergola system is generally inferior to other systems in terms of the quality of fruit it produces appears not to be true, at least when it comes to a vigorous variety like Viognier.

With VSP, their yield is 10-12,000 kg per ha, but with the pergola system, not only is the yield much greater at 20,000 kg per ha but the quality is much higher.

Francisco explained that with VSP, Viognier enters a vicious circle which is difficult to break once established – vigour increases while quality decreases.

This is a good counter-argument example for the MW essay question, ‘Low yield equals quality'! "

Another photo:

All this seems interesting.  Maybe I'm being too simple, but the soil health seems to trump all arguments.  More shade means healthier soil.  Healthy soil should produce higher quality fruit.  This is Texas.  There is a lot more sum than even in southern France.  It seems that grape growers at latitudes similar to Texas tend to use pergolas, those in more northern latitudes use trellis.  This is particularly true in earlier times with more sustainable practices were in use.


I wonder how this issue could be settled scientifically?