FERTILISER GUIDELINES FOR THE WINE INDUSTRY

thus create favourable conditions for diseases, as well as decreased sunlight penetration, with negative effects on particularly colour, but also general quality. Low carbohydrate reserves and large cells can contribute to the frost sensitivity of grapevines. The plant hormone auxin inhibits length growth but stimulates branching, and there is a direct correlation between N-supply and auxin production. Conse quently N-nutrition results in thicker and more branched root growth, while roots are long, thin and sparsely branched in a Ndeficient medium, like in bleached sands. Maximum fruit yield is obtained at a lower N-nutrient level than that at which maximum vegetative growth is obtained. At suboptimal N-supply, nodes are ini tially adversely affected by low Nnutrient levels, resulting in a low yield during the next season. Deficient Nnutrition can lead to a low Ncontent in must and subsequent poor fermentation and wine quality, as opposed to N-rich must that ferments faster resulting in a higher ester synthesis, which is beneficial for wine quality. Nitrogen is seen as a mobile element because N-compounds in older leaves, which no longer function very actively, hydrolise and the fragments (probably amino acids) are translocated to younger plant parts. Deficiency symptoms,

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FIGURE 3: General yellowing of leaves and poor growth due to Ndeficiency.

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