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Crop Specific
Irrigation
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| Onions |
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| The
National onion average works out at 18 tons per acre, but it
is possible to double this and more. One must assume that a
grower plants good seed, at the appropriate density, into a
suitable seedbed, applies about the right amount of fertiliser
and acheives good disease control. With good germination the
only difference between the best crops and the average must
be water. This page explains watering onions. These two pictures
show the difference between two watering regimes. Without doubt
there will be large variations in quality and yield. This page
discusses how water and hence nutrients will affect the final
product. |
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What
are the important factors in watering onions?
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Irrigation systems
- Germination
- Soil
condition
- Early
season watering
- Main
bulking period
- End
of watering\necking over
- Harvesting
- Storage
1.
Irrigation systems:
Most
people use Rain Guns, which are inapropriate when the crop
is small or for encouraging germination. The drops tend to
be too large drops of water, which can compact the soil.
See section on Rain Guns.
Booms, Linears and Pivots are very good for applying small
amounts of water early in the season and on a lot of soils,
throughout the season. However, they do put the water on very
fast, which can be a problem on some soils. You need to measure
and calibrate to match application and infiltration rates.
Mini Sprinklers are useful for applying small amounts of water
regularly, but have the disadvantage of all overhead systems
of wetting the foliage and encouraging disease. Drip can be
the 'perfect' answer, but can be expensive if you get it wrong.
Check it out - it is often much cheaper than you think! See
drip section.
|
Drip irrigated onions on the left and boom
irrigated (not well!) on the right. |
2.
Germination is often a problem - being
able to apply small gentle amounts of water can help considerably.
Try applying small amounts and see if there is a difference.
3.
Soil condition can inhibit good germination
as some soils are left far too 'fluffy' which can result in
the seeds drying out.
4.
Early season watering can be very important,
as any 'down time' in growth rate, when the crop is small with
shallow rooting, will effect the final yield. Often all that
is required is 'little and often' water. Many growers lack good
data to take decsions on early season watering.
5. Bulking
for drilled crops is usually from the beginning
of July to mid-August. Rooting depth can be from 10cm only to
at least 50cm. The grower needs to be aware of rooting depth
and use an appropriate watering regime. It is perfectly possible
for onions to need 25mm every 4 to 5 days to grow at maximum
speed. |
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| The
above graph shows a couple of water applications, neither of
which refilled the soil, even in the top 30cm. You can see that
the crop used 16mm of water in 3 days and then only 4mm in 4
days. Remember: Yield is proportional to water use and, moreover,
any slow down in the crop's use of water not only reduces yield,
but is likely to affect quality too.The best watered onions
also seem to keep the best. |
| 6.
When to finish watering? There is no
point in having an extra 3 tons per acre if the crop will not
store; so, doing your own trials is the best way to learn. But,
it is interesting to note that in wet Septembers it is still
possible to have good quality onions. If one is monitoring,
it is easy to see what happens and then repeat it in a dryer
year. If in doubt, water a small area and see if there is any
benefit or not. Often in dry times it is very difficult to harvest
onions as the soil is so hard - with good monitoring you can
learn the best way to overcome this. Always keep crops that
have been treated differently in separate places so that you
can learn which one stores the best. |
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IrrigationWorld2000.com
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