FERTILISER GUIDELINES FOR THE WINE INDUSTRY

HANDLING OF THE SAMPLES: Place the composite sample in a clean plastic bag. Label the bag with name and the sample identity. If several composite samples were taken, label each one differently and keep a record of the areas where each sample was taken. Only one form needs to be filled out for each group of samples. The more complete the information provided, the better the ultimate laboratory recom mendation will be.

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LEAF SAMPLING

The aim of leaf analysis is to relate the mineral content of the plant to its physical appearance, growth rate and yield or quality of the harvest. The in terpretation of results depends on the assumption that a significant biological relationship exists between the elemental content of the vine and its growth and/or production. This technique requires sampling at the correct phenological stage (time of sampling) according to a specific protocol. Leaf analysis can serve as a diagnostic tool for wine grapes, but has the shortcoming that in practice it is often influenced by factors such as scion and rootstock cultivar, cultivation practices, cultivation area, seasonal climate, diseases and soil type. A general norm that makes provision for all conditions, therefore, is inevitably very wide-ranging. Leaf analysis can consequently not be used as the only norm for establishing a fertilisation programme, but should be seen as supplementary to soil analyses. Leaf analysis can be useful, however, in case studies. In such cases, leaves are sampled in a specific way from the “sick” vines, in addition to a similar sample from adjacent, nonaffected vines. The leaves from the healthy/better vines then serve as direct control and the time of sampling and all other vari ables are less critical or not applicable. No norm is used, but rather the relative differences between the two samples. The purpose of leaf analysis can therefore be summarised as follows: • To serve as an aid to evaluate the supplying capacity of the soil for nutri tional elements; • To evaluate the effect of treatments on the nutritional status of the vine; • To evaluate the relationship between the soil nutrient status and the plant reaction as an aid to estimate fertiliser requirement; • To diagnose suspected deficiencies of nutritional elements.

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