FERTILISATION GUIDELINES FOR THE TABLE GRAPE INDUSTRY

CHAPTER 2

Handling of the samples The composite sample is placed in a clean plastic bag and the bag is labelled with a name and the sample identity. If several composite samples were taken, each one must be labelled differently, and a record must be kept of the areas where each individual sample was taken. Only one form needs to be completed for each group of samples. The more complete the information provided, the better the recommen- dations will be. LEAF SAMPLI NG Leaf analysis can serve as a diagnostic tool for table grapes, but in practice it has the shortcoming that it is often affected by factors such as scion and rootstock combination, cultivation practices, cultivation area, seasonal climate, diseases and soil type. A general norm that makes provision for all conditions is, therefore, inevitably has a very wide range. Consequently, leaf analysis cannot be used as the only norm for establishing a fertilisation programme but should be supplementary to soil analysis. Leaf analysis can also be useful in case studies where leaves are sampled from “sick” vines, in addition to being sampled from adjacent, unaffected vines. The leaves from the healthy/better vines then serve as direct control, so that the time of sampling and all other variables 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: • It assists in evaluating the capacity of a soil to supply nutritional elements, and consequently serves as an aid to determine fertiliser calculations; • It indicates the effectiveness of fertiliser treatments on the nutritional status of grapevines; and • In instances where nutritional deficiencies are suspected, diagnosis can be done correctly. Time of sampling Leaf samples should be collected annually at the same physiological growth stage. In this regard fruit set or veraison can be used. Fruit set is understood to be the period extending from the end of flowering up to the pea berry stage (berries with a diameter of approximately 5 mm). At the time of veraison older leaves are often very dilapidated, but for certain elements like potassium (K), veraison remains a good time to sample. Leaf blade or petiole For vineyards in which the nutritional status varies, the petiole normally indicates larger differences than the leaf blade. The composition of the petiole also differs to a greater extent within the same vineyard compared to the leaf blade. Furthermore, the boron status is reflected better by the leaf blade than by the petiole. It is thus recommended

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