Handbook for Irrigation of Wine Grapes in South Africa

Chapter 9

soil wet will increase the capacity to absorb heat during the day, thereby reducing the risk of cold damage. However, excessive irrigation may cause waterlogging, particularly in poorly drained and flood irrigated soils, and cause unnecessary leaching of nutrients. Wet, smoothly rolled and compact soil surfaces without weeds will also absorb more heat during the day that can be irradiated in the night (Fig. 9.9). The frost level is usually just above the cover crops, which could be in line with the sprouting buds or new growth (Fig. 9.10A). Therefore, herbicides must be applied to kill cover crops and high growing weeds before budbreak. In order to lower the frost level closer to the soil surface, cover crops must be rolled flat or mowed before budbreak (Fig. 9.10B).

FIGURE 9.9. A growing weed stand causes the soil to absorb less heat during the day.

A

B

FIGURE 9.10. The frost level is usually just above the cover crops (A), therefore they should be mowed or rolled flat to bring the frost level closer to the soil surface (B).

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