South Africa Wine Technical Yearbook 2025

material can release nutrients at a later stage when broken down in the soil. The accumulation of reserves late in the season is notably impacted by stress factors such as drought, waterlogging, high crop load and poor cultivation practices such as disease control. The quality and length of the growing period after harvest play a major role here, therefore unnecessary leaf fall due to diseases or mechanical harvesting should be prevented at all costs. If vines have few or no active leaves, the post-harvest fertilisation should rather be applied in the following season as extra nutrition. The uptake of macro-nutrients over the season can be seen in Figures 1, 2 and 3. Three macro-elements will be discussed separately, in terms of the vine’s post-harvest requirement when maintenance fertilisation is applied. Nitrogen Nitrogen recommendations are mainly calculated according to the vigour required. The wine goal is also a good indication of the desired growth, with moderate growth recommended for quality. In the case of mass bearers, more growth will be recommended. The post-harvest nitrogen fertilisation should comprise about one-third of the total season’s fertilisation to ensure enough reserves for the next season’s bud break. Keep in mind however that poor growth is not always attributable to insufficient nitrogen applications alone, as the following factors can also play a significant role: • Waterlogging. • Dehydration. • Salinisation. • Nutrient deficiencies. • Aluminium toxicity in low pH soils. • Root pruning at the wrong time. • Competition from weeds for water and nutrients, especially in the case of couch grass and other perennial crops. • Nematodes. • Phylloxera.

FIGURE 1. Seasonal uptake of nitrogen by Chenin blanc/99R in sand culture.

FIGURE 2. Seasonal uptake of potassium by Chenin blanc/99R in sand culture.

FIGURE 3. Seasonal uptake of phosphorus by Chenin blanc/99R in sand culture.

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TECHNICAL YEARBOOK 2025