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mercredi, 18 septembre 2013

IRRIGATION

VINE IRRIGATION: THE GOOD THE BAD AND THE UGLY ?


Claude Gilois

The term irrigation has a negative connotation and, in Europe, it is often associated with high yields, hence poor quality. Irrigation has long been considered a New World practise for varietal wines (as opposed to the ultimate, terroir driven wines), which by inference were of lower quality. 

However, climatic changes are reshuffling the deck and Italy, by a decree published on 19th April 2013, has authorised irrigation in all regions where it was not strictly forbidden by local regulations in all its major wine regions covering DOC, DOCG and IGT in severe droughts and heat waves.  The decree follows a series of particularly hot vintages and many growers describe 2012 as an ‘annus horribilis’ that can be compared to 2003, the last canicular year in Europe. 

Other countries will have to take similar measures in the long-term; this includes France, where the authorities are at present considering these kinds of measures. Angelo Gaja, never short of an opinion on Italian wines declares: ‘Droughts and canicular temperatures caused yields to be markedly reduced in 2012. These adverse conditions also prevailed in 2007, 2008, 2009 and 2011 so that we have now moved from a situation of surplus to a deficit which is fast becoming chronic’.    Paradoxically, in countries such as California, where irrigated viticulture is now the norm, there are talks of returning to dry farmed viticulture, as the shortage of water is likely to become chronic with climatic changes.    

We have known for a long time that water is a means to increase yields and this is why the use of water on vines was forbidden in Europe, but lack of water is also the best way to reduce yields to a point where viticulture becomes uneconomical or price of wine has to be exorbitant.  However, as we have seen in a previous article, the relationship between yields and quality is not entirely linear and the correlation between low yields and quality is far from perfect. 

There are people, for example Claude Bourguignon, an academic and guru of the soil, who cannot conceive viticulture with irrigation and who think that wine should not be produced in regions that have a deficit in rainfall too important to conduct dry farmed viticulture.  At the opposite end of the spectrum, there are those, in particular the viticulturists from irrigated vineyards who argue that the vine is a plant and a plant needs water to survive, and irrigation does not interfere in any major way with the quality of the grapes or the wines if controlled drip-feed irrigation is applied. However, for Claude Bourguignon, water is an essential component of the terroir on a par with soil and sunlight. 

 

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Drip feed irrigation

Water is not only necessary for photosynthesis, but it is also necessary to replace water loss from evapotranspiration, a natural process which comes from evaporation and sweating and which depends largely on ambient humidity. It is estimated that one vine will use 6,500 litres of water during the maturation of grapes and 180,000 litres of water per hectare is necessary to compensate the loss of water during maturation. So it is easy to understand that, in the context of global warming with water becoming scarcer, viticulture depending on irrigation might not be sustainable.

 

Australia, which is facing repeated droughts and with its water supply depending on decreasing resources from the Murray Darling basin, is already disengaging itself from industrial viticulture, which is very water intensive, for the production of entry- level wines which were Australia’s big success on the export market in the 1990’s. 

The San Joachim Valley in California with its extensive planting competing for scarce water resources, and countries such as Chile and Argentina are particularly vulnerable to climatic changes as their water supplies depend largely on the melting snow from the Andes which is particularly vulnerable to climatic changes. 

Water used for irrigation contains salt, which, over time, causes an increased saltiness of the terroirs and the wines, unless it is leached from the soil by applying more water that the vine has lost by evapotranspiration, which is difficult without compromising quality. 

Eben Saddie, from the Saddie Family winery, an aficionado of old non-irrigated vines used for his wine declares: ‘Irrigation levels-up and standardises vintages’. It is a criticism that is difficult to refute and vintages from the New World are more evenly distributed over time than vintages from the Old World. However, it is one of the main reasons that these wines have become popular with consumers as it guarantees them a consistent quality irrespective of the vintage. Fine wine, up to a point, (which many notorious wine regions get past to produce unremarkable wines in some years), vintage variation is most certainly better for informed customers. 

Water stress is on the whole beneficial to plants as it not only reduces the yields, but also the size of the berries, hence increasing the ratio between skin and pulp and it is in the skin that the most interesting components such as phenols, tannins and aromas are found, improving, in the end, the quality of the juice and ultimately the wine. 

However, irrigation can be particularly useful when there is a heat wave and a drought, which induce a gap between physiological maturity and sugar concentration. By controlled irrigation it is possible to avoid picking before full maturation or preventing dehydration and shrivelling of grapes on the vine. 

As we have seen before on many occasions, there are no definite answers in viticulture and wine making, it is all about compromise to get the best possible results. Too much irrigation will increase the canopy at the expense of the grape and produce diluted and green flavours; too much water stress will produce reduced yields, too much fruit concentration, and a lack of harmony in wine, and angular and austere tannins. 

In regions where irrigated viticulture has now become the norm, mostly in the New World, water availability will probably be severely curtailed and viticulturists will have to move towards a more traditional viticulture by using techniques such as selective root zone drying (a technique designed to trick to plant into thinking it is water stressed while there is enough water provided) or by deficit irrigation.  As for some of the Old World wine regions, they will have to get used to selective drip feed irrigation as is now practised in the best regions of the New World.

 

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