Handbook for Irrigation of Wine Grapes in South Africa

Chapter 4

70 000

Dryland Drippers Micro-sprinklers Overhead sprinklers Flood irrigation

60 000

50 000

40 000

30 000

Area (ha)

20 000

10 000

0

1983 1987 1991 1995 1999 2003 2007 2011 2015

Year

FIGURE 4.1. Temporal changes in dryland viticulture, as well as irrigation systems used in South African wine grape vineyards (Data supplied by SAWIS).

Figure 4.2

by the SABS. Poor water quality can also affect the longevity of irrigation systems. Refer to Chapter 5 for guidelines concerning irrigation water quality, and the management thereof. Since irrigation water resources are generally limited, it is essential that water losses during application should be as low as possible. In this regard, irrigation systems inherently differ with respect to water losses while irrigations are being applied. In fact, the so-called “irrigation system efficiency” differs considerably between the systems used in vineyards (Table 4.1). For example, given that the efficiency is 80% for micro-sprinklers, it means that only 80% of the water leaving the micro-sprinkler will reach the soil surface. The 20% loss is usually caused by evaporation as the water droplets travel through the air. These losses will increase if high air temperature and/or strong winds prevail. TABLE 4.1. Irrigation system efficiencies according to Ley (1994). Irrigation system Efficiency (%) Flood (border, rill) 45 to 60 Sprinklers - portable 60 to 70 Micro-sprinklers 75 to 85 Drip (trickle) 85 to 90 Subsurface drip 90 to 95

IRRIGATION OF WINE GRAPES 73