FERTILISER GUIDELINES FOR THE WINE INDUSTRY

2

TIME OF SAMPLING: Leaf samples should be collected annually at the same physiological growth stage. In this regard flowering, fruit set or veraison can be used. Leaf compo sition changes very rapidly during flowering, to such an extent that it is some times difficult to interpret figures obtained at this stage. On the other hand, the older leaves by the time of veraison are often already very dilapidated which makes it difficult to collect a representative sample, but for certain elements like potassium (K) for example, veraison remains a good time for sampling. The most practical compromise that is reasonably satisfying for most elements, is to collect samples during the fruit set period. Fruit set is understood to be the period stretching from the end of flowering until the pea berry stage (berries with a diameter of approximately 5 mm). This period lasts at least 3 weeks and for most cultivars in the Western Cape, the last week in November will usually fall within this time frame. LEAF BLADE OR PETIOLE? For vineyards, which have differing nutritional status, the petiole normally indicates greater differences than the leaf blade. On the other hand, the com position of the petiole also differs to a greater extent within the same vineyard than is the case for the leaf blade. Furthermore, the boron status is better reflected by the leaf blade than the petiole. As a point of departure it is thus recommended that the petiole is sampled for analysis at fruit set. In certain cases, however, it will also be necessary to analyse the leaf blade. Norms for the elemental contents of leaf blades and petioles are indicated in Chapter 5.

12