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The Essential Role of Nutrition in Viticulture
Factors Influenced By Nutrition
 | Sugar content of must
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| Acidity of must (keeping quality of wine)
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| Anthocyanin content (red wines)
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| Tannin content (important for colour stability)
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| Composition of other phenolic compounds (flavour, bouquet of wine)
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| Level of production (important for blended wines to ensure sufficient quantities of each variety) |
Factors Affecting Must Quality
| Harvest date (sugar/acid ratio in berries)
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| Even maturity of grapes at harvest, which is dependant on...
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| A`tight', well grouped flowering
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| Good photosynthesis throughout the season
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| A correct mineral balance throughout the season |
Boron, Zinc and Phosphorus affect Flowering
| Deficiencies can cause... |
Flower abortion (coulure)
| This is a problem for the production of blended wines (where a uniform wine quality is required) |
Boron, Zinc and Phosphorus deficiencies affect Fruit Set
| Poor fruit set and uneven ripening (millerandage) which lead to...
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| musts with reduced sugar content
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| increased acidity
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| lack of colour (unripe grapes)
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| problems of colour stability (improperly developed berries contain high level of tannins which causes an imbalance in the tannin:anthocyanin ratio)
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| Astringent wines with unripe tannins which are unpleasant (agressifs), without quality (grossiers), smelling of grass (herbacés) because pips and stalks stay green |
Analysis of a thousand leaf samples showed...
(Using Industry recognised critical levels)
Nutrient
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Number of samples below the critical level at flowering
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Boron
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54 %
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Phosphorus
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40 %
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Zinc
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42 %
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Photosynthesis
Magnesium and iron improve photosynthesis without the negative effects of nitrogen. A poor photosynthesis results in:
| Low energy reserves within the plant leading to.... |
- problems of coulure and millerandage
- low sugar (alcohol) content | Early leaf fall leading to.... |
| Premature senescence of vineyard |
Analysis of a thousand leaf samples showed...
(Using Industry recognised critical levels)
Nutrient
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Number of samples below the critical level at flowering
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Nitrogen
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11% (66% too high)
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Magnesium
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71 %
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Iron
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69 %
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Fruit Swelling and Ripening - Priority Nutrients
| Magnesium
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| Potassium
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| Their balance is a determining factor for... |
- sugar transport to the berries
- the occurrence of grape stalk necrosis (GSN) which stops the ripening process
- Potassium has a major influence on must acidity
Grape Stalk Necrosis results in...
| Loss of up to 2o in sugar content likely in the must
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| Lack of colour because berries stay green (less anthocyanins)
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| Problem of colour stability due to an excess of tannins (T/A ratio too high)
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| Excessive acidity (ripening stopped)
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| Lack of flavour/bouquet (oxidation of phenolic substances) |
Effect of Potassium on Must Acidity
| An excess of potassium neutralises the tartric and malic acids in the must and can cause a lack of acidity
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| A lack of acidity leads to poor storage potential of the wine |
- especially if the lack of acidity is not compensated by a good tannin structure | Conversely a lack of potassium can lead to excessive acidity |
Analysis of a thousand leaf samples as showed...
(Using Industry recognised critical levels)
Nutrient
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Number of samples below the critical level at ripening
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Magnesium
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66 %
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Potassium
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12 % (15 % too high)
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