FERTILISATION GUIDELINES FOR THE TABLE GRAPE INDUSTRY

CHAPTER 7

7 THE RELATIONSHIP

BETWEEN FERTILISATION, THE NUTRITIONAL STATUS OF A VINEYARD AND GRAPE QUALITY The role and function of the most important macro- and micro-elements in the grapevine were discussed in Chapter 5. As indicated, most of the nutrients influence grape quality, either as single elements or as a group, either directly or indirectly. The direct effect is related to the quantities of nutrients present in the soil, grapevine and/or grapes – either deficiently or excessively. A deficiency of nutrients can be detrimental to the physiological and/or biochemical processes in the grapevine, while an excess can be toxic. The deficiency of a specific nutrient develops when limited uptake of that element takes place, when there are insufficient quantities of the element in the soil, or insufficient water is present in the soil to facilitate uptake, or the roots have become damaged (e.g. nematodes), or where one element is present in such excess that the uptake of another nutrient is negatively affected. Furthermore, nutrient uptake is dependent on soil pH which determines the availability of the element. The ideal soil pH KCl for good nutrient uptake is 5.5 – 6.5. The indirect effects of nutrients manifest as either negative or positive growth effects as affected by a nutrient deficiency or a nutrient excess. The vigour and management of the vineyard determine the canopy characteristics and light relationship of the canopy. The exposure of bunches, together with the efficacy of the canopy has a large effect on the ultimate grape composition and subsequent storage potential/grape quality. The most P I ETER RAATH & KOBUS CONRAD I E

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