Handbook for Irrigation of Wine Grapes in South Africa

Evaporation: Soil texture % Wetted area

Transpiration: Leaf area per grapevine Canopy orientation Plant spacing

Atmospheric conditions: Reflects in the reference evapotranspiration

Chapter 8

Figure 8.6 , irrigation cycle and amount of irrigation are summarized for each month in a table. For convenience, irrigations are expressed as depth of water (mm), volume (m 3 ) and runtime (hours) per irrigation. If the number of irrigations per season is less than ten, only the dates on which the irrigations are required and the amount per irrigation on those days is displayed, instead of the monthly table. Using the VINET model version 1.1 to determine the irrigation requirements for a low frequency irrigated vineyard near Stellenbosch is demonstrated below. Note that only 10 irrigation blocks can be entered per file (Figs. 8.6 to 8.16). If more blocks need to be processed, there is a facility to create additional files. (%) is also required. The PAW depletion levels will depend on the yield or wine quality objectives as discussed in Chapter 7. The model outputs comprise leaf area index (m 2 leaves x m 2 soil surface), irrigation application rate (mm/h), bruto irrigation requirement (mm) and the number of irrigations. Furthermore, the daily ET, k c

FIGURE 8.6. Background information menu for the VINET model. The default for “Begin year” is the year in which the model is being run. Other regions are the Northern Cape or Northern Provinces, i.e. Gauteng, Limpopo and Mpumalanga.

IRRIGATION OF WINE GRAPES 243