FERTILISER GUIDELINES FOR THE WINE INDUSTRY

The effectiveness and economy of Feapplications on calcareous soil are questionable and in such cases only a foliar spray with 0.1-0.15%-Fe-chelate (FeEDTA) can be recommended upon the first appearance of symptoms. This must be repeated at weekly intervals, up to a maximum of 6. A case of a Fedeficiency has been observed on acidic sandy soil, which developed from grey Table Mountain Sandstone. Here the cause was a total deficiency of Fe in the soil and not the inaccessibility due to high pH. On acidic soil a Fe-EDTA-application of about 1 kg ha -1 can be considered. Manganese (Mn) It is responsible for activation of a large variety of enzyme systems and is inter alia also involved in carbohydrate metabolism, phosphorylation, the citric acid cycle etc. It is also essential for chlorophyll formation and is an ingredient of chloroplasts where the Hill reaction rate is proportional to it. It also plays a role in the reduction of nitrates to i.a. ammonium. An excess Mn is toxic for the plant. There is a large variety of minerals that contain Mn and it is also found in the organic fraction of soils as humic acid complexes. Manganese deficiencies are predominantly induced by high pH soil condi tions, where it is masked by Fedeficiencies. It is also often observed on the acidic soils of the Western Cape, especially in the early spring when the soil is still cold. Moderate Mndeficiencies apparently have no effect on growth and yield. The correlation between the total Mn-content of soil and the accessibility there of for plants is poor. The use of EDTA extractant in determining ‘accessible’ Mn is an arbitrary process which imitates the ability of the plant to obtain Mn. For soils with a pH KCl of between 5.0 and 6.5, the total Mn-content should amount to at least 2.0 mg.kg -1 (see Table 5 in Chapter 3). In cases where the micro-element contents of soil are very low, it is expensive to ‘fertilise the soil’ in an effort to obtain a satisfactory analysis and the philoso phy should rather be to ensure that sufficient microelements are present in the immediate root environment of the vine. For Mn the recommendation is thus to apply 20 kg ha -1 Mn-sulphate via the irrigation system or in suspension on the berms of existing vineyards and in the case of new plantings on the future vine rows just before planting holes are made. Manganese is relatively immobile in plants but deficiency symptoms in grape vines first appear on older leaves. The symptoms are light, general interveinal

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