Agriculture Reference
In-Depth Information
it can stand in the field and be harvested throughout the winter. Crop storage for
2-4 months, depending on storage facilities, is feasible (see Chapter 7), and can
be used to supply the market when fresh standing crops are not available.
Transplants
Various systems of transplant production are used, including bare root trans-
plants, peat blocks and modular trays containing about 15 ml of compost per
cell. Blocks and modules may be multi-seeded for planting as two- or three-
seedling clusters. The production regime is similar to that for onion (see above).
Typically, 18°C will be applied for the first 3 weeks from sowing, followed by
14°C, with 10°C for a week or two before planting to harden the plants. Seed-
lings are slow growing and plant-raising usually takes 8-12 weeks, depending
on light and temperature (see 'Leeks, growth and development' in Chapter 4)
and the size of transplant required.
In UK trials, seedlings sown in 27 mm peat blocks on 20 January reached
the same weight by 29 March (0.45 g) as seedlings sown 3 weeks earlier into
15 ml cells in modular trays, so rooting volume and medium can be important.
The longer the seedlings are growing before planting, especially if exposed to
low temperature, the sooner the leeks bolt (see Fig. 4.52), so treatments that
promote rapid growth to transplanting size are preferable.
Yields and mean plant weights at harvest correlate well with mean weight
at transplanting. For example, Benjamin (1984) raised seedlings in peat blocks
from a 30 March sowing and 7 weeks later graded them into large, medium and
small sizes, which had mean fresh weights of 0.619, 0.451 and 0.214 g,
respectively, and planted them in separate plots. At harvest, 221 days later, the
corresponding mean plant weights were 299, 261 and 217g. Therefore, for
early production, large seedlings are preferable. Also, the yield of maincrop leeks
decreases as planting is delayed from May onwards (see Fig. 4.50 and Table 4.7).
To compensate, the Dutch recommend planting seedlings of 3.0-3.5 mm
diameter in May, but of 5-6 mm in July.
Leeks are commonly planted on a bed system, typically in rows about 30 cm
apart. If they are to be earthed-up during growth they may be planted in the base
of furrows. In the UK, a typical transplanted maincrop would be sown in mid-
March, transplanted at about 40 plants/m
2
in early June, given a basal fertilizer
application of 130:60:160 kg/ha of N:P:K, followed by an additional application
of 150 kg/ha of N in mid-August and irrigated during dry periods. Residual
herbicides are applied to the beds, and pesticides to control thrips and leek rust
are usually necessary (see Chapter 5). Under such a regime in variety trials at
Luddington, central England, mean total yields and yields of leeks greater than
25 mm diameter were, respectively (in t/ha) 30.2 and 19.3 on 29 September, 40
and 33.5 on 24 November and 40 and 34 on 2 February. By 7 May 78% of the
plants were visibly bolting and therefore unmarketable.
