Soil–Water–Vine Relationships and Water Management - Soils for Fine Wines - page 166

Irrigation Systems 6.6

Irrigation systems may be broadly divided into microirrigation systems, made
up of drip (or trickle) systems, microjets, and minisprinklers, and macroirrigation
systems, comprising overhead sprinklers, traveling irrigators, and flood/furrow
systems.
The choice of which system to use depends on several factors, including the
availability and price of water, the topography and soil type in the vineyard, cap-
ital costs of installation, and the skill of the vineyard manager. However, the ef-
ficiency of water use (from pump to soil) is normally highest for drip systems
(90%), intermediate for sprinklers (60-80%), and lowest for surface furrow and
flood systems ( 50%).

Microirrigation Systems
Details of the construction and performance of these systems are given in spe-
cialized irrigation topics, such as by Dasberg and Or (1999) or Mitchell and Good-
win (1996).
Drip systems consist of emitters spaced at regular intervals along flexible PVC
pipes that run along the vine rows. Individual emitters deliver water at rates be-
tween 1 and 8 L/hr. Drip lines may be placed above ground or below, the latter
being called subsurface drip irrigation ( SDI ). For SDI , the lateral pipes are laid
1-2 m apart at depths of 0.4-0.5 m, depending on the soil depth and hydraulic
conductivity. Many of the advantages and disadvantages of drip irrigation and SDI
are similar (table 6.5). However, some aspects specific to SDI are the following:
• Root invasion and consequent blockage can occur. To prevent this, the
irrigation water filters or the in-line drippers are impregnated with the
herbicide trifluralin (“Treflan”). Root invasion is also minimized by
keeping the soil around the drippers moist most of the time.
• If the system develops a fault, a vacuum may develop which sucks water
and soil into the emitters. Vacuum relief valves should be installed at the
head of the system and at high points along the laterals. The system should
be flushed frequently to prevent blockages and inhibit root invasion.
• There is no wet soil surface under the vines, which reduces the risk of
fungal infections, such as downy mildew, powdery mildew, and botrytis.
• Soil evaporation is reduced, hence there is no need for mulch, which can
be a fire and frost hazard in some orchards.
Microjets deliver water at a rate of 32-40 L/hr compared to a rate of 50-100
L/hr with minisprinklers . A microjet can be directed to give a uniform band of
wet soil in the vine row and can be inverted for young vines to reduce the wet-
ted area. Minisprinklers wet a larger soil area than microjets or drippers. Wetting
with a minisprinkler is more uniform than with a microjet, provided the operat-
ing pressure is adequate. If a minisprinkler is operated at pressures 150 kPa, the
wetting pattern is a nonuniform “doughnut” shape. Both microjets and minis-
prinklers require filtered water, or water with a low concentration of suspended
solids, to avoid blockages.
Neither microjets nor minisprinklers are as effective as drippers in saving wa-
ter (see appendix 10).

6.6.1