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58
GRAANGIDS
2016
GRAIN GUIDE
IRRIGATION
– steps to consider
To ensure that irrigation succeeds, there are certain basic things that must be in place and that you
should know before you can start thinking about irrigation:
In the first place here must be a
reliable and sustainable water source
in the vicinity. For
information on rivers, contact the Department of Water Affairs.
If the above is in place, the further condition is that the
water must be suitable for irrigation
.
This means that there should not be too many salts or other harmful elements in the water.
This can be a problem with borehole water in many cases. In dams and rivers there can be
biological problems with the water. In order to determine whether the water is suitable, have it
tested at a water analysis laboratory.
The third requirement is that you should have
soil that is suitable for irrigation
. The impor-
tant thing here is that it should be a medium to heavy soil. Pure sand has very little water
retention capacity and is not suitable for irrigation. The soil should have enough depth and
there should be no limiting layer too close to the surface. The soil should be chemically suit-
able for cropping, and there are also further requirements for irrigation. To make sure of
these, a number of profile holes should be dug up to a depth of 1 m, soil samples at a few
different depths should be taken from the holes and tested by a soil analysis laboratory.
A further requirement with respect to the soil is the
topography of the field
. Fields that are too
steep cannot be tilled safely with implements, and this creates pressure problems with respect
to irrigation, in addition to erosion hazards.
Although
climate
does not place as great a restriction on irrigation as do the crops that can
be planted, it is a factor to be taken into account. In this case it would particularly affect the
type of irrigation system that can be used. For example, it is not ideal to use a sprinkler system
where there are constant strong winds or very high temperatures. Drip irrigation would be
preferable in such areas.
Availability of energy
is a major requirement. In view of the high cost of fuel, it is not eco-
nomic to use engines to pump water, and electricity in the area is essential, whether supplied
by Eskom or by turbines in a river, or water under pressure from higher-lying dams, which
is ideal.
Only when all the above factors are in place can you start thinking about an
irrigation
system
. The main factor that determines the type of system to be used is the type of crop
that you want to irrigate. The availability of a supplier that is located not too far away is also
important, particularly with respect to aftersales service for the irrigation system that is going
to be purchased.
Even more important than the type of system is the ‘type’ of
installer of the system
. You can
have all the right things in place and have everything of the best, but if the installation is not
carried out correctly, you will have a system that will give you infinite problems in the future.
The
system must be managed
correctly in all respects. Irrigation systems are expensive, and
if you do not get the maximum efficiency from your system, you will struggle to pay for it.
Irrigation has become science, and you should therefore use all the
irrigation and scheduling
aids
that are available. Automatic weather stations are no longer a luxury, but are essential,
as the irrigation information researchers make available these days is based on weather data.
AS van Niekerk, Pr Eng., ARC-Institute for Agricultural Engineering