Agriculture Reference
In-Depth Information
seedheads (Gray
et al.
, 1992). Unlike onion, seed moisture content is not a
reliable guide as to when to harvest. Normally, the seedheads are harvested
with 15-30 cm of stalk attached and placed to dry at 20-35°C for 4-6 weeks.
After this, the seedheads can be threshed, the seed extracted and cleaned and
stored at low temperature and humidity, as for onion (see above).
Seed dormancy and size
Leek seeds sometimes show high-temperature dormancy, with slow and low
germination at temperatures > 20°C from seedlots that have good germinability
at lower temperatures. This occurs when seedheads develop at cool temperatures
(e.g. 15°C) and is avoided if seedheads develop and dry at mean temperatures of
20°C or above (Gray
et al.
, 1992). Smaller seeds are formed when seedheads ripen
at warm rather than at cool temperatures, because the duration of seed growth is
shorter at warm temperatures (see Fig. 6.18a). There is no general correlation
between seed viability and seed size, but a correlation between seed weight and
transplant size has been demonstrated (de Clerq and van Bockstaele, 2002).
The culture of these onions is described by Inden and Asahira (1990), and by
Larkcom (1991). They are sold in various forms: (i) as small, green bunching
onions; (ii) as green shoots 40-90 cm long with tender, green leaves plus one-
quarter to one-third of the length as white pseudostem; and (iii) as long, blanched
pseudostems, similar in appearance to the large leeks of Europe. By harvest time
the green leaves on the latter types tend to be tough, and are discarded.
Cultivars for blanched pseudostem production do not branch freely and
fall within the 'Kaga' and 'Senju' groups according to their winter hardiness
and growth rate at cool temperatures (see Chapter 1). The hardy types, which
survive over winter in cold regions, grow slowly at low temperatures (see
Chapter 1). Types for green shoot production branch more freely and
predominate in the 'Kujyo' group. Green shoots may be harvested any time
from 40 days to 12 months after sowing, depending on size at harvest and time
of year. Early spring growth is often accelerated by using polythene tunnels.
For blanched pseudostem production in Japan, seeds are spring-sown for
harvest the following winter, or autumn-sown and spring-transplanted for
summer, autumn and winter harvest. The seedlings are transplanted into
furrows about 15 cm deep with about 9 cm between plants in the row. Three
or four times during growth, earth is pulled round the pseudostems so that
ultimately they are growing in earthed-up ridges. Fertilizers are applied three
or four times during the growing season, typically applying totals of 200, 150
and 175 kg/ha of N, P and K, respectively. The harvested pseudostems vary in
length and thickness, but can be up to 50 cm long and 3.5 cm wide.
