Handbook for Irrigation of Wine Grapes in South Africa

Chapter 4

Each micro-sprinkler design has a unique water distribution pattern. Within a specific design, the distribution pattern is primarily a function of (i) the water discharge rate through the base or nozzle, (ii) the design of the cap or spreader and (iii) the pressure head within the irrigation system (Fig. 4.14). Micro-sprinklers with high discharge bases or nozzles should be avoided on soils where the high precipitation rate could cause runoff losses (Fig. 4.14A). Preferably, micro-sprinklers should spread the water evenly across the wetting pattern to wet the soil homogenously. However, in practice, this is not the case. The precipitation rate generally tends to be high near the micro-sprinkler, and low near the edge of the wetted area (Fig. 4.14A, B & C). This usually results in unevenly wetted soil (Myburgh & Piaget, 1990). Furthermore, it must be noted that an increase in water pressure may only increase the precipitation rate near the micro-sprinkler (Fig. 4.14C). Therefore, micro-sprinklers with more uniform distribution patterns are preferred to obtain homogeneous soil wetting. For most micro-sprinklers, details of the technical specifications are readily obtainable from the irrigation equipment manufacturers or dealers.

12

A

A

/oZ IloZ no]]le PediuP range sZivel +igh IloZ no]]le PediuP range sZivel

10

8

6

4

2

3recipitation (PP h)

0

0 0 25 0 5 0 75 1 1 25 1 5 1 75 2 2 25 2 5 2 75 3 3 25 3 5

Distance IroP Picro-sprinkler (P)

0 1 2 3 4 5 6 7 8 9 10 0 0 25 0 5 0 75 1 1 25 1 5 1 75 2 2 25 2 5 2 75 3 3 25 3 5 3 75 4 3recipitation (PP h) Distance IroP Picro-sprinkler (P) /oZ IloZ no]]le PediuP range sZivel /oZ IloZ no]]le long range sZivel 0 1 2 3 4 5 6 7 8 0 0 25 0 5 0 75 1 1 25 1 5 1 75 2 2 25 2 5 2 75 3 3recipitation (PP h) Distance IroP Picro-sprinkler (P) 10 P 3ressure loZ IloZ no]]le PediuP range sZivel 15 P 3ressure loZ IloZ no]]le PediuP range sZivel 20 P 3ressure loZ IloZ no]]le PediuP range sZivel B C B C

FIGURE 4.14. Examples of (A) nozzle size, (B) swivel range and (C) water pressure effects on water distribution patterns around micro-sprinklers.

IRRIGATION OF WINE GRAPES 81