Handbook for Irrigation of Wine Grapes in South Africa

Chapter 7

FIGURE 7.43. Example where excessive pressure causes a fine mist that will increase evaporation losses.

Since less energy is available for evaporation from the soil surface during the night, compared to daytime, evaporation losses will be less if irrigation is applied during the night. In some areas, wind speeds are also lower during the night, compared to daytime conditions. Therefore, irrigation water will be applied more efficiently at night, particularly where the full surface is wetted by means of overhead sprinklers or micro-sprinklers. Evaporation losses between the orifice and the soil will also increase under windy conditions, particularly if the air temperature is high (Fig. 7.44). Therefore, it would be better to irrigate during the night where strong winds usually prevail during daytime. Evaporation losses from the soil surface will also be less when atmospheric conditions are cooler during the night.

IRRIGATION OF WINE GRAPES 227