Handbook for Irrigation of Wine Grapes in South Africa

Chapter 4

FIGURE 4.19. An example of a micro-sprinkler fitted with an anti-bug cap in the closed and the open position on the left and right, respectively.

4.2.3 MOVEABLE SPRINKLERS Due to high labour inputs and relatively low system efficiency, compared to drip and micro-sprinklers, overhead sprinklers became less popular over time (Fig. 4.1). Overhead sprinklers distribute the water over larger areas than micro-sprinklers. Consequently, the discharge rates and radii of overhead sprinklers are substantially higher, compared to micro-sprinklers. It must be noted that Equation 4.5 can also be used to calculate the precipitation rate for overhead sprinklers. For example, if overhead sprinklers are spaced 6 by 6 m, and the discharge rate is 450  /h, the precipitation rate of the system will be 12.5 mm/h. Since the orifices are wider, overhead sprinklers are less prone to clogging than micro-sprinklers. To reduce the risk of theft, plastic overhead sprinklers should be installed rather than the more conventional brass ones (Fig. 4.20). Since overhead sprinklers inevitably wet the grapevine canopies (Fig. 4.21), it is not suitable where the irrigation water quality is poor. Excessive salt accumulation may damage leaves if the water is saline. Furthermore, elements such as chlorine may be absorbed to toxic levels over time if the leaves are wetted.

FIGURE 4.20. Example of a plastic overhead sprinkler.

IRRIGATION OF WINE GRAPES 85