FERTILISATION GUIDELINES FOR THE TABLE GRAPE INDUSTRY

CHAPTER 5

In existing vineyards, it is endeavoured to, at least, increase the P level of the upper horizon (0 – 300 mm) to the optimum level. Annual applications on the basis of production (as indicated in Table 8) will only be necessary in instances where soils have high pH values (pH KC) > 7, or pH water > 8), where P is quickly fixed, and for drip irrigated vineyards where fertilisers are applied hydroponically. Phosphorous is easily mobilised within the vine and deficiency symptoms are rarely observed in vineyards, because they are not specific. Symptoms are described as diminished growth, dark green leaves, occasional purple colouration of the main veins and a smaller angle between the main vein and the petiole. These symptoms are only identifiable when compared directly with a vine that is adequately nourished (Figure 6) and can therefore not serve as a reliable indicator for the necessity of P nutrition.

FIGURE 6: No clear deficiency symptoms for P deficiency, only diminished growth (Saayman, 1981).

Leaf norms (Table 15) can be used in a supplementary manner, although the same restrictions apply as already discussed for N.

TABLE 15: Norms for the P content (%) of leaf blades and petioles of grapevines.

Fruit set

Veraison

Leaf blade Petiole Minimum High Minimum High Minimum High Minimum High 0.14 0.55 0.20 0.63 0.26 0.45 0.09 0.64 Petiole Leaf blade

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