FERTILISATION GUIDELINES FOR THE TABLE GRAPE INDUSTRY

CHAPTER 5

FIGURE 11: Necrotic pedicels (left) and pedicel attachments (right) associated with berry stem necrosis for table grapes (Photos: P. Raath).

Application of sprays to the leaves and bunches, aimed at increasing the Ca content of the berries to improve quality, were found to be ineffective in several experiments in South Africa (Raath, 2012), as well as in Chile (personal communication: Prof. Juan Pablo Zoffoli, 2009). This is ascribed to the fact that Ca is predominantly transported in the xylem and that the xylem in the berry becomes inactive after veraison. As shown in Table 19 (Conradie, 1980), 64% of the bunch’s Ca requirement is already supplied between bud break and pea size, followed by 35% between pea size and veraison and only 1% between veraison and harvest. This indicates that the Ca requirement of the bunch is largely supplied during the first part of the growing season, thus confirming that Ca sprays applied during the latter part of the pre-harvest period are unlikely to have an effect.

TABLE 19: Provision of calcium to bunches from bud break to harvest, based on a production of 30 ton per hectare.

Growth stage Bud break to pea size Pea size to veraison Veraison to harvest

Requirement/ provision to bunches

Bunch requirement (% of annual requirement) Fraction (%) supplied by the soil Absolute amount accumulated in bunches (kg ha –1 )

64

35

1.0

100

100

100

3.3

1.8

0.1

In practice soils that are adequately supplied with Ca (normally neutral to high pH soils) will supply sufficient Ca to the grapevine. Soils with low pH values are normally limed to pH KCl 5.5, which will increase the Ca status of the soil and will ensure a Ca saturation of approximately 80%. For vineyards with Ca contents of > 2.5 cmol kg –1 (500 mg kg –1 )

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