FERTILISER GUIDELINES FOR THE WINE INDUSTRY

• In terms of the indirect influence, there is a direct correlation between the nitrogen levels in a grapevine and the shoot growth. At high or excessive levels, (overly) luxurious growing conditions can be induced with resultant dense canopies where the trellis system is insufficient and/or poor canopy management is applied. Dense canopies lead to high pH in must due to high potassium translocation to the bunches and the binding with tartrates and excretion of K-bitartrates during and after the crushing action, which in turn lead to lower acidities and high pH. Less tartaric acid is also produced under dense canopy conditions and malic acid constitutes a larger component of the total titratable acids. • The decreased aeration within the dense canopies also increases the risk of fungal diseases and rot which can cause decreased quality and even offodours in the wine. The decreased light exposure of the bunches also results in decreased colour formation for red grapes. • The excess nitrogen can also lead to larger, “bloated” berries as a result of the excessively luxurious growing conditions, which can have a dilution effect on colourants and flavourants and is naturally detrimental for quality production. • An excess nitrogen in relation to potassium in a vineyard during the spring period can lead to “false symptoms of Kdeficiency”. Phosphate Very few facts regarding the direct role of P on grape composition and wine quality/character exist, but it is known that Pdeficiencies can lead to diminished growth and fruit set, which can also impact on grape composition and wine style/quality. Potassium • It is generally accepted that soils with high K-levels (naturally of due to K-fertilisation) in particular, inevitably give rise to high levels in the grapes and ultimately the wine. A further presumption is that high K-levels in the grapevine lead to high levels in the grapes, which in turn lead to high pH/ low acidity in must and wine, which is problematic for especially red wines. Both these assumptions appear to be not entirely correct.

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