Page 25 - Landscape-Issue141

IRRIGATION FEATURE

Water distribution test
The layout below shows the test setup for each soil. Drippers delivering 0.5 ℓ/h,1.0 ℓ/h and
2.0 ℓ/h were tested with 3 ℓ, 6 ℓ and 9 ℓ buckets and appropriate irrigation times.

Jovan Erasmus conducting a profile pit water
distribution test

without rapidly reducing the levels of
oxygen in the root zone. An ideal point
of balance between water and oxygen,
at which plants will thrive, exists for each
soil type. When irrigating, the aim is to
manage the root zone with precision in
order to maintain the perfect soil-water
balance.
A low infiltrability rate combined with
a high flow rate will lead to very wide The best way to appreciate the results is through the graphs below that illustrate the water
horizontal distribution, but very shallow distribution pattern formed. Note that each colour represents a different dripper delivery rate.
vertical distribution. This often leads
to ponding, high run-off and shallow
rootzones. By lowering the delivery
rate, distribution is more uniform with
balanced horizontal and vertical water
distribution and a more balanced oxygen
level.
Low delivery rates make the necessary
balance possible by achieving good
infiltration in moist soils. The forces of
gravity and capillary action become more
equal and soil/ water/air ratios can be kept
more constant throughout the wetted area.

Soil water distribution test
For this test, use a five to ten litre bucket Lessons learnt from these Knowing this information is important when
on a platform, raised 40cm from the soil experiments considering dripper spacing selection and
surface. Connect a dripper with a chosen • Proper soil preparation makes all the irrigation duration.
flow rate to a thin pipe. Connect the other difference in achieving balanced water When considering the above graphs,
end of this pipe to the bottom of the distribution and ensuring healthy root you will note that the 0,5 ℓ/h dripper had
bucket and place the dripper end on the zones. the widest spread and did not wet the soil
soil. Allow the bucket to run empty and • The lower the flow rate, the better the as deeply as the 1 and 2 ℓ/h drippers. This
you can open a profile pit to look at the balance between the horizontal and indicates that with lower flow, you will have
water distribution pattern. vertical distribution of water. better control over your depth of irrigation,
• Soil compaction will have a massive impact whilst also maintaining more constant
Case studies on the distribution of water in your soil. oxygen levels in the soil. You are also less likely
Netafim conducted experiments on farms Compaction layers generally occur at to leach fertilisers past your root zone.
in Tzaneen, Letsitele and Nelspruit to different depths in the soil. Water distribution is impacted by many
test the water distribution patterns for • Water tends to accumulate above factors and dripper spacing, dripper delivery
different flow rates in different soils. It is compaction layers, thus spreading rate and irrigation duration must all be
extremely important to know the soil you horizontally above the layer. The top layer selected with care to ensure a healthy root-
are working with. Without knowledge of soil will then become saturated, which zone. There are many decisions that must
about how water moves through the means that there will be little or no oxygen be made, and understanding soil and water
soil in question, calculations are futile. It in the soil. movement and plant requirements makes it
is important that these tests are done in a lot easier to make these decisions. Lastly, be
very dry soil, otherwise it will be difficult Determining dripper spacing sure to involve the necessary experts in the
to see and feel the difference in the soil. To determine dripper spacing, note the width planning process as a long list of variables
Netafim did water distribution tests and and depth of the water distribution pattern must be measured, considered and analysed.
dug profile pits to physically measure the in your soil; you will then have insight into
wetted area. what goes on underneath the soil surface. Photos supplied by Netafim SA
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