FERTILISATION GUIDELINES FOR THE TABLE GRAPE INDUSTRY

Fertilisation can thus be effective only if the root zone is healthy and managed properly. A healthy root zone is therefore the “buffer”, helping the producer and the vineyard to overcome unfavourable environment/climate situations. Correct time of application – the placement of nutrients in the correct ratios within the root zone ensures that it will be assimilated by the grapevines during the season, as required. There are two approaches for managing fertiliser applications: Constant nutrition – the vineyard’s calculated NPK requirement is applied proportionally over the course of the season. This approach ensures that all nutrients are available in balanced ratios throughout the season, and that the plant can assimilate according to requirement. Rectification fertilisation – the P and K requirements are rectified according to the norms in Chapter 5 and thereafter there is mainly fertilised with N. This practice is better suited for soils with high clay contents and where granular products are used. In Table 10 of Chapter 5 the seasonal uptake of N, P, K, Ca and Mg over the course of the season is indicated and expressed as a percentage of the annual uptake for each growth stage. These uptake patterns can be used as guidelines to divide the annual requirement into suitable instalments. Because vigour is the most important factor denoting N fertilisation practices, it should be evaluated during each phenological stage, and N fertilisation levels must be adjusted accordingly (Table 12 of Chapter 5). Due to the necessity of having a fully developed leaf canopy at flowering already, while vigour should slow down closer to veraison, N fertilisation levels are likely to deviate from the normal seasonal pattern for N uptake. For vineyards with average vigour, stronger emphasis on N fertilisation before flowering may be necessary, but less than the requirement for the growth stage can be applied between fruit set and veraison. As indicated in Chapter 5, the growth season of the grapevine may be divided in four phases that may also be used as the phases for fertiliser applications. Bud break to bloom – during this phase the largest percentage of the grapevine’s vegetative growth takes place. For early cultivars this phase may be very short. Also take note of the comment on soil temperature, later in this chapter. After fruit set – adequate canopy/leaf surface area shortly after fruit set is required to enable the grapevines to optimise the necessary berry enlargement and ripening processes. Veraison – maximum translocation of sugar and colour development must be ensured during the ripening period. In this period active vegetative growth must not compete with bunches for carbohydrates from the leaves. However, enough nutrients for satisfying the nutrient requirements of the grapevines must be available.

84 | PRACTICAL GUIDELINES FOR IMPLEMENTATION OF THE FERTILISATION PROGRAMME