FERTILISER GUIDELINES FOR THE WINE INDUSTRY

Where the Ca:Mg ratio is ≥6, the amount of lime required for every 300 mm soil layer is calculated as follows: tons lime ha -1 = [(H x 10) – (Ca + Mg)] x 0.727

If the Ca:Mg ratio is <6, the formula is: tons lime ha -1 = [(H x 10) – (Ca x 1,25)] x 0.727

Distinction must be made between the two kinds of lime that may be applied, namely calcitic lime (CaCO 3 ) and dolomitic lime (CaMg(CO 3 ) 2 ). Dolomitic lime must only be applied if the Ca:Mg ratio is higher than 6 and/or if the Mg content of soils indicate minimum values as indicated in Table 3. Calcitic lime is used when the Ca:Mg ratio is 6 or lower. Since lime is not easily soluble in water it moves very slowly in the soil. Con sequently it should be applied during soil preparation so that it can be worked into and mixed with the soil to a depth of 1 000 mm. If the pH is lower than 5.5 in existing vineyards, the lime requirement should only be calculated to a soil depth of 300 mm. Grapevines are lime tolerant and grow well in soils containing free lime, with pHs KCl around 7.2. Excessive lime application therefore should normally not be harmful. Soils with high stone fractions can however be seen as an exception, and in such cases it is important to take the stone fraction into consideration.

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The calculated lime requirement therefore should be adjusted downwards, using the stone volume percentage in the following formula:

Lime requirement x [1 – (stone %/100)]

In soils with high organic material contents, a low pH is largely caused by hydrogen ions associated with the organic material, and to a lesser degree by hydrogen ions created by high concentrations of aluminium. The exchange able H, determined at a pH of 7, therefore should be adjusted for soils with C contents of >1%. The adjusted H can then be used in the Eksteen formula.

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