| Irrigation
of top fruit is not an important activity in the UK at present,
but as the customers insist on improved taste and shelf life
will become more so! |
| However,
throughout the world watering top fruit is very important.
Most growers will be using some form of mini sprinklers or
drip. But the principles are much the same. |
|
The
grower needs to know:
- The
rooting depth of his trees.
- The
spread of the roots.
- Where
in that spread the most water use occurs.
- How
much water will the soil hold when full.
- When
to water.
- How
much to apply.
- When
to water again.
|
|
Having
established all of the above (using good accurate water
monitoring equipment) the grower then needs to do his own
experiments on what produces the required quality and yield.
|
|
Too
much water may reduce storeage life and affect the taste
of the fruit.
Too
little water may reduce yield and encourage cracking.
Then
after doing all this work the fruit will then be affected
by the nutrients available at different times during the
season.
|
|
Early
in the season there may be few active roots due to
prolonged wet spells and the death of root hairs. Certainly
in hot dry countries watering at this time is very important,
especially as this is the time of maximum calcium uptake.
Post
blossom the roots will be developing
to their normal rooting depth -
but the grower will need to know if his crop is using water
as in other years. It can be that the rooting is shallower
and therfore he must water sooner with smaller amounts.
Water use in the UK is normally quite small at this time.
Fruit
fill is the time of maximum water
use and any loss of uptake due to a shortage of water in
the soil can cost the grower a lot of money.
|
|
An
example of the happenings under the trees.
A typical intensive tree
may take up 6sqm
and have a rooting depth down to 50cm by the middle of the
season. In this example the trees are watered by mini sprinklers,
which cover the whole of the rooting area and the soil type
is a medium loam.
|
|
Rooting
depth
|
Total
water, when 'full'.
|
Total
Water
|
Available
water depending on rooting depth
|
At
5mm per day water use - number of days from 'full'
to 'refill'.
|
|
10cm
|
35%
|
35mm
|
17mm
|
3.5
days
|
|
20cm
|
35%
|
35mm
|
35mm
|
7
days
|
|
30cm
|
35%
|
35mm
|
55mm
|
11
days
|
|
40cm
|
35%
|
35mm
|
70mm
|
14
days
|
|
50cm
|
35%
|
35mm
|
80mm
|
16
days
|
|
|
What
happens if the trees are watered with drip, which only wets
50% of the rooting area or much less?
Once the tree has run out of water over the whole rooting
area and the drip is started it has to get all it's needs
from only 50% of the root volume. The grower needs to know
whether it can do this. Assuming that it can, the tree will
use water from the 'wet' areas twice as quickly, because
there is none in the dry area. If the wetting volume is
even less - 10% is common, then the water use in the wet
spot can be 50mm per day. On some light soils, which only
hold 30mm, watering once per day may not be enough.
The
grower needs to know, so he can make better decisions. He
needs to monitor correctly.
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