Handbook for Irrigation of Wine Grapes in South Africa

Véraison

Harvest

Flowering

Pea size

Budbreak

1 Irrigation - normal winter - drier winter 2 Irrigations - normal winter - drier winter 3 Irrigations - normal winter - drier winter 4 Irrigations - normal winter - drier winter

FIGURE 7.26. Schematic illustration of irrigation based on phenological phases when irrigation water is limited.

If there is enough water for two irrigations, and the winter rainfall was normal, the irrigations should be applied at pea size berries and véraison (Fig. 7.26). If the soils are relatively dry at budbreak, the two irrigations should be applied before flowering and at véraison. Irrigation at these stages will reduce the risk of small berries and possible yield losses caused by excessively warm conditions during berry ripening. If there is enough water for three irrigations, and the winter rainfall was normal, the irrigations can be applied at pea size, véraison and half way through berry ripening (Fig. 7.26). In the case of low winter rainfall, the three irrigations can be applied before flowering, at pea size and at véraison. The application of a fourth irrigation is illustrated in Figure 7.26. If there is not enough irrigation water available to irrigate all the blocks as discussed above, the water must only be used for high income and young vineyards. The latter are important since the future sustainable production of the farm depends on the well-being of the young vineyards. If possible, planting of new vineyards should be postponed until the irrigation water resources have been restored. In situations where the water reservoir(s) that feed the irrigation scheme did not fill sufficiently during relatively dry winters, it is possible that water allocations could be drastically restricted, or even cut off. If there is enough time for a round of irrigations in the period between the announcement of the cut-off and the actual cut-off date, a single, deep irrigation should be applied during that period.

7.2.11

PRACTICES TO REDUCE UNNECESSARY WATER LOSSES

A number of long or short term measures can be implemented to reduce water losses, particularly when drought conditions prevail, or when periodic droughts

214 CHAPTER 7 – IRRIGATION STRATEGIES