Agriculture Reference
In-Depth Information
Table 6.5.
Water productivities of onion crops under different methods of irrigation.
Water
Water use
productivity
efficiency
Plant
for bulbs
for bulbs
Type of
density
(FW/ET
c
,
(DW/ET
c
,
Author(s)
irrigation
(plants/m
2
)
kg/m
3
)
Kg/m
3
)
Notes
Al-Jamal
et al
.
Furrow
NA
4.60
0.49
On commercial
(2001)
fields
Al-Jamal
et al
.
Sprinkler
28.4
8.40
0.90
(2001)
Ells
et al.
(1993)
Furrow
NA
9.70
NA
Martin de Santa
NA
25
12.20
1.10
Olalla
et al
.
(1994)
Shock
et al
.
Drip
25
12.40
NA
Fertigation
(2004)
Shock
et al
.
Drip
35
15.00
NA
Fertigation
(2004)
Bosch-Serra
Drip
80
19.15
1.61
Fertigation
(1999)
NA, not available.
Harvesting
The harvesting techniques suitable for bulb onions depend upon weather at
harvest time. In areas where warm, dry weather occurs reliably, the curing and
bagging of the crop can be done in the field. In wetter, temperate regions,
mechanical harvesting and artificial heating and ventilation for drying are
essential to produce reliably high quality bulbs on a large scale. The purpose of
curing is to dry the neck of the bulb so that it seals, and prevents the entry of
disease organisms, and to produce dry, well-coloured outer skins that are not
split.
The traditional method of harvesting involves pulling the bulbs from the
soil, or undercutting them, and then laying them in rows (windrows) on the
ground to dry and cure. In areas with strong sunshine the bulbs must be
protected from direct insolation by covering them with leaves while lying
outside, otherwise they can be damaged by 'sunscald', which kills the outer soft
scale tissue, disfigures the bulbs and may allow bulb-rotting organisms to
develop. The bulbs may be left in such rows for 1-2 weeks before removing the
foliage and packing in crates or sacks.
If the onions are fairly mature, with soft, near-dry necks, then in dry
climates the foliage may be removed when the bulbs are pulled from the soil
and the bulb necks left to dry in rows or in stacks of trays (Jones and Mann,
