South Africa Wine Technical Yearbook 2025

JANUARY/FEBRUARY

Post-harvest strategy for maximum reserve accumulation in grapevines By Klaas Coetzee

Insufficient leaf surface to ensure adequate post-harvest fertilisation uptake.

In the case of early cultivars, root growth takes place approximately two weeks after the harvest period, but for late cultivars it can start during the harvest already. During the post harvest period, a grapevine takes up approximately 38% of its nitrogen requirement, 23% of its phosphate requirement and 16% of its potassium requirement. This can vary depending on the area, cultivar and rootstock combinations, but it does emphasise the importance of good post-harvest fertilisation. If sufficient post-harvest irrigation or rain is not available to wash in the fertiliser, it is important to establish cover crops and fertilise them well to ensure that the organic

season. The first occurs at the beginning of the growing season right after budding, which is the most important time for nutrient uptake. It is also important to understand that from budding to flowering the grapevine mostly depends on its reserves established during the previous growing season’s post harvest fertilisation. Vine leaves contribute to production until the leaf on the primary shoot reaches 50% of its mature size, and 75% of its mature size when the leaf is located on a branch shoot. The second root growth stage commences during, or right after the harvest period, depending on the ripening period of the cultivar.

The storage of carbohydrate reserves mainly takes place in the trunk and root cortex, after which it is used by means of enzyme activity for predominantly new root growth. Ample root reserves play a big role in the bud break of the next year, as well as bunch ripening at the end of the season. One tonne of grapes removes approximately 3 - 4 kg of nitrogen, 0.7 kg phosphate and 3 kg potassium per season. In cases where carbon and soil microbe activity are sufficient and therefore able to break down the shoots and leaves quickly enough, these amounts can however differ. There are two main root growth stages during the plant’s growing

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TECHNICAL YEARBOOK 2025