Handbook for Irrigation of Wine Grapes in South Africa

Figure 4.30

A

B

PHOTO: NETAFIM SA

PHOTO: NETAFIM SA

FIGURE 4.30 . Examples of (A) slime and (B) rotten roots plus slime in drippers that had been installed 30 cm below the soil surface for four years.

Figure 4.31 In order to improve the water use efficiency of full surface flood irrigation, the water can be applied by means of slotted 50 mm ø PVC drainage pipes buried ca. 30 cm deep alongside the grapevine rows. The objective of this practice is to create a high volume, low pressure irri ation system. However, the above-mentioned field trial showed that this subsurface system also had no advantage in terms of yield or water use efficiency, compared to furrows or conventional drip irrigation (Table 4.4). Similar to the subsurface drip, the drainage pipes showed considerable clogging after four years. In this case, the clogging was not due to root penetration, but by deposits of fine soil in the drainage pipes (Fig. 4.31). It is uncertain whether the soil was sucked into the pipes when irrigations were stopped, or merely seeped into the pipes while irrigations were being applied. Subsurface porous pipe (Fig. 4.32), also referred to as “Leaky pipe”, became completely clogged within two years. Consequently, the porous pipe had to be replaced by above-ground drip to prevent the grapevines from dying. In contrast, porous pipe did not become clogged where saline borehole water was used for irrigation of table grapes near Vanrhynsdorp (Myburgh, 2012b). In fact, porous pipe induced no negative effects on yield or fruit quality, compared to micro-sprinklers or above-ground drippers.

FIGURE 4.31. An example of severe clogging where irrigation was applied by means of 50 mm slotted drainage pipe that was installed 30 cm below the soil surface for six years.

94 CHAPTER 4 – IRRIGATION SYSTEMS