Page 13 - Vol.38-No.8

CROP PROTECTION

MICRO-SPRINKLER

TECHNIQUES FOR FRUIT TREES

multi-purpose it has been quite widely used micro-sprinklers makes for easier use and
for fertigation and chemigation, frost pro- application of soil monitoring equipment
tection in orchards and evaporative cooling and instruments.
in greenhouses. The pattern of root distribution is a close
Water requirements for a micro-sprin- and complete reflection of the distribution
kler system are usually determined by the of water in the soil and numerous field tri-
DR. TERRY MABBETT evaporation rate from the crop and/or soil als comparing micro-sprinkling and other
or by measurements of soil water con- methods of irrigation (including classical
tent. Early tests showed that efficiency drip irrigation) in orchard tree crops show
Micro-irrigation is defined as the ap-
plication of water to less than 100 per of micro-sprinklers at between 94 to 97 distinct differences in pattern of root dis-
cent of a crop area. Micro-irrigation covers per cent were higher than for any other tribution.
both drip/trickle and micro-sprinkler/mi- method of irrigation under use. This ultra In the micro-sprinkler treatment the
cro-jet irrigation systems. Each possesses high efficiency was attributed to uniform roots are evenly distributed in the area/vol-
advantages and disadvantages and may be wetting of the irrigated area and to the ume of wetted soil and grow to a depth of
modified and adapted to different crops, correctness and exactness of the amounts some 80 cm, as well as being far greater in
soil types and climatic conditions. As a gen- of water that were being applied. number. On the other hand roots in classical
eral rule of thumb drip irrigation systems Use of micro-sprinklers means the drip irrigated treatments are concentrated
have found widest application in row crop amount of water needed by the plants is in a relatively shallow and small volume
vegetables and bush/vine crops while mi- applied to a set volume of soil. This strategy of soil beneath the dripper. Furthermore
cro-sprinklers have proved most popular in allows the root system to develop evenly micro-sprinkling produces a superior tree
fruit tree crop orchards and groves. and spread densely throughout the entire canopy/root system relationship that is
volume of soil that has been wetted. Thus much better balanced.
if micro-sprinklers are the main means of
water application throughout the year trees
are assured of a continuous and adequate
supply of water and nutrients.
This is in complete contrast to orchards
and groves where tree crops are predomi-
nantly rain fed and only need irrigation for
relatively short but critical periods of time
during the dry season. In this situation the
tree’s root system develops according to
the natural rainfall. Only the micro-sprinkler
Apricot suffering in the heat of the with its modular design and wide range of
South Australian summer
(Picture Dr Terry Mabbett) options is capable of supplying the required
quantity of water and nutrients accurately
Micro-sprinklers for tree and efficiently to the already developed
root system during this critical dry season
crops period.
Micro-sprinkler irrigation systems are The uniform rate of irrigation provided by
designed to deliver and distribute water micro-sprinkling means it is relatively easy
as a fine rain-like shower of drops. Water is to calculate the amount of water required Climatic and soil conditions where olives
generally transported to and into the field by each tree. With the low irrigation vol- are typically grown makes the trees and
through a network of tubes. It is subse- ume applied there is no problem with water groves ideal for micro-sprinkler irrigation
quently applied to the crop using a series of ‘runoff’ or water ‘ponding’ on the surface of (Picture Dr Terry Mabbett)
micro-sprinkler devices to achieve localised the soil and irrigation rate is easily matched
but highly efficient and effective irrigation. to soil type and climatic conditions. And Only some 40 to 80 per cent of soil sur-
The main difference between delivery by a through application of optimum amounts face area is wetted with micro-sprinklers
micro-sprinkler and a micro-jet is that with of water there will not be any seepage in mature orchards but may be adjusted
the former the water jet rotates while in out beyond the root zone nor problems according to the pattern and extent of
the latter it is static. Micro-sprinkling has of aeration within the root zone caused root development without incurring any
usually been used purely for application of by water-logging of the soil. Furthermore, extra costs. In addition the shape of the
water to crops, but being adaptable and uniform wetting of the soil through using wetted surface area may be altered from
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