Agriculture Reference
In-Depth Information
seedheads are threshed and the seed cleaned. Yields of 0.6-0.9 t/ha are typical
(Bonnet, 1976). Compared with onion, leek seedheads are slow to develop, and
it takes approximately 50% longer in terms of day-degrees (> 6°C) after
flowering for leek seeds to reach ripeness (Gray and Ward, 1987).
Consequently, seedheads are often harvested in late autumn after the onset of
damp weather, and this may contribute to the poor quality of many seedlots.
Production in polyethylene tunnels
Trials in the UK have shown that 1.5-2.5 t/ha of seed with about 90%
germination can be produced consistently from year to year in polyethylene
tunnels (Gray et al. , 1991b). The production method involves sowing for
steckling production in June, followed by the transplanting of 1.0-1.5 cm-
diameter stecklings, at 50-60 plants/m 2 , to tunnels in mid-winter or early
spring with basal N, P and K levels of 72, 224 and 224 kg/ha. To avoid wetting
the foliage, trickle irrigation is used. Flowering usually occurs over 5-6 weeks,
starting in mid-June, and during this time blowflies are introduced and
replenished weekly using about 3.4 l of blowfly pupae/100 m 2 of tunnel area.
The optimum time for harvesting is when the seeds have blackened but before
the capsules open and start to lose seeds by shedding. At this stage the seed still
has a moisture content of about 60% (see Fig. 6.18b).
Provided seed is left to dry and ripen within the capsule, high-quality seed
results even though seedheads are harvested at an immature stage. Seed
growth and the development of germinability continue after harvesting of the
Fig. 6.18. (a) Change in mean leek seed dry weight with time at 20/10 (
), 25/15
(
) day/night. Data are averages of 3 years of experiment; vertical
bar = LSD ( P = 0.05). (b) Loss of seed moisture content during development of leek
versus day-degrees > 6°C after flowering. Key:
) and 30/20°C (
, majority of seeds black;
, capsule splits; a, endosperm milky; b, 'soft cheese' endosperm; c, 'hard cheese';
d, flint hard. Standard error less than symbol size (from Gray et al. , 1992. Courtesy
of Seed Science Research).
Search WWH ::




Custom Search