FERTILISER GUIDELINES FOR THE WINE INDUSTRY

TABLE 14: Norms for the K-contents (%) of leaf blades and petioles of grapevines (Conradie, 1994).

Fruit set

Leaf blade

Petiole

Minimum

Maximum

Minimum

Maximum

0.65

1.30

1.00

2.90

Veraison

Leaf blade

Petiole

Minimum

Maximum

Minimum

Maximum

0.55

1.05

0.90

1.80

Calcium (Ca) It is abundant in grapevine organs and the content thereof increases over the season. Calcium is found in the vine in solution form, as well as fixed as oxalate crystals and as Ca-pectate in the middle lamella of cells. It thus constitutes a part of cell membranes and plays a role in the transport of material in the conductive tissue, as well as the permeability of cell walls and the forming of certain proteins and enzymes. Calcium is considered relatively immobile, although in perennial plants it evidently goes into solution again in old tissue and moves predominantly apically and is i.a. involved in the development of growing tips. There is thus an upward flow of Ca from the soil through the vine, which ultimately ends up on the soil as leaves and prunnings, and consequent ly there is little Ca-removal by means of the harvest. Calcium is one of the most abundant elements in nature, but the presence thereof varies greatly based on the composition of the parent material and the intensity of erosion and leaching. It is found in a large variety of primary mate rials, like feldspars (plagioclase), pyroxenes and amphyboles, but especially as secondary minerals like calcite, dolomite and gypsum. It is also usually the most prominent exchangeable cation, even in acidic soils. Calcium deficiency symptoms have, as far as is known, not been observed under field conditions. In acidic soils, where Casupply is low and deficiency symptoms can be expected, other aspects like aluminium and/or manganese toxicities prevail. In Southern France it has been found that acidic soil toxicities (Fig. 10) can be combatted more effectively with dolomitic rather than calcitic lime, probably due to an uptake antagonism between Mg from dolomitic lime and the AI and Mn in the soil.

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