That nursery rhyme could not more perfectly describe my current feelings about the British weather. Please, send me to southern Spain or California - where the sunshine is plentiful and wine is delicious, and vice versa. Or alternatively, just stop this continual soggyness.
Yet, for all this complaining we are actually quite lucky as the reverse situation of water shortages and unpredictable precipitation can wreak havoc on agriculture and increases the need for irrigation, impacting on both the economy (increasing the investment in irrigation technologies) and ecology (draining water from surrounding areas and altering the water table). Indeed, British agriculture does not have to deal with water shortages on any long term basis, which is unfortunately common in semi-arid areas of Australia, USA, and South Africa and which is now becoming more prevalent in southern Europe.
But let us speak more specifically of my favourite crop - Vitis vinifera. Traditionally, it's crop that does not require irrigation with cultivation being restricted by climate and soil charateristics, similar to those preferred by the indigenous V. vinifera. This typically spans the region between 30-50° North and 30-50° South of the Equator. However, expansion into warmer areas, such as South Africa, Australia and Lebanon in combination with climatic extremes, increasing water scarcity, unpredictable rainfall and rises in temperatures are forcing growers to implement irrigation schedules. Methods such as regulated deficit irrigation (RDI) and partial rootzone drying (PRD) irrigation have become an integral part of viticultural practices in both the arid and temperate regions of grapevine cultivation. With a strong foundation in molecular and physiological sciences, these techniques are enabling growers to maximise yield while maintaining and even enhancing grape quality under unfavourable environmental conditions.
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| Modern Irrigation - Full vs. RDI vs. PRD |
Modern irrigation strategies, which aim to supply each vine with ~50% of its water requirement, are no longer focusing on production per unit soil area, but rather the emphasis is on maximising water productivity, i.e. the production per unit of consumed water, for both economic and ecological reasons. To achieve an increased production per unit of consumed water requires manipulation of the vine water use efficiency. Such manipulation has been shown to increase not only the weight of fruit produced but also quality of fruit per unit of irrigation water applied.
These findings are particularly important as full irrigation techniques (the vine is supplied with 100% of its water requirement) are both costly to the grower and subject to government restrictions on the amount of water available for use - hose pipe ban anyone? Hence the need to develop low water-input irrigation practices as well as identifying varietals displaying high water use efficiencies.
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| Vineyard Irrigation |
And let us not forget terroir and the all important interactions between soil and vine. With water shortages, the most threatened vineyards are those on steep slopes with low water holding capacity soils with water being lost as run-off creating a large water deficit. With further research into these interactions there is the possibility for matching terroir and varietal to minimise the impact of water loss and scarcity.
However, this reliance on modern irrigation is far from ideal as it has both economic and ecological costs, in addition to changing grapevine morphology. An increased water supply has various negative impacts on vine health and has traditionally been seen as a last resort - it's pure heresy according to biodynamic producers. The major detrimental impact is increasing shoot vigour and vegetative (leaf and stem) growth. Compounds needed for berry development and growth are redistributed to growing leaves. An increase in leaf number increases the amount of water lost through transpiration and leaf shading reduces berry quality and increases the chances of pathogen (insects, fungi, bacteria and virus) infection.
But what one makes up for in some areas, one lacks in others. While British vineyards very rarely reach the water and temperature thresholds that would require the implementation of irrigation strategies we don't receive adequate sunshine. Not enough sunshine leads to inconsistent yields. Hence, some vineyards do not print the vintage on the bottle label. We just can't seem to win!
So, Mr Rain and your cloud-like friends,
Take a nice little holiday away from Britain and venture to southern Spain or California. Both Vitis vinifera and I would greatly appreciate it!
Yours Sincerely,
Bacchante
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