Biomedical Engineering Reference
In-Depth Information
moist conditions. Shoots are produced from dormant vegetative buds. Therefore,
the commercial crop is produced by planting winter dormant, woody stem cuttings,
usually of about 20 cm length and 15 mm diameter.
Willow seed does not contain endosperm, an individual seed weighs only a few
milligrams. This makes them difficult to store in a viable condition. Seeds are
collected at capsule dehiscence, this typically this occurs 4-6 weeks post pollina-
tion [
28
,
30
]. Although seed storage protocols exist [
31
,
32
], following crossing the
resultant seeds are germinated almost immediately. Seedlings are reared in a glass
house before being transferred to an outdoor irrigated nursery in June. The progeny
seedlings produce a single stem of 2 m or more in height in their first growing
season. All further reproduction is vegetative from stem cuttings and there is no
further use of seeds in the multiplication of willow. The F
1
generation is subjected
to selection and ultimately multiplication for sale.
Once selected as a cultivar, multiplication beds are planted specifically to
produce stems for planting new areas. These beds are planted at greater density
than a commercial wood production field. Often 40,000 cuttings will be planted per
hectare on a 0.5
0.5 m grid compared to 15-17,000 cuttings per hectare on a
double row system in wood production. The high planting density ensures that low
diameter, straight, branch-free stems which are optimal for machine planting are
produced. After grading and trimming to 2 m long, such beds may produce up to
600,000 new cuttings (at 20 cm length) which represents a multiplication ratio of
15:1 on a cutting basis, but 40:1 on an area basis when planting new crop at 15,000
cuttings per hectare.
Some commercial nurseries now also utilize micro-propagation techniques to
multiply new genetic material more rapidly. This has a financial cost but may be
justified by early market entry. Such micro-propagation methods may also be
valuable to overcome phytosanitary restrictions on movements of stem material
between territories.
Market Challenges/Barriers to Commercialization/
Opportunities
Recently, SRC willow production has sat awkwardly between agriculture and
forestry. Surplus grain production in Europe, low commodity prices, and land
set-aside schemes provided a place for energy crops on arable farms. The recent
changes in arable farming fortunes have totally reversed the situation. Fortunately
willow is an immensely flexible crop now finding a more suitable niche in tradi-
tionally non-arable areas. The one potential drawback of this change has been the
difficulties experienced with winter harvesting on wet land in northwestern Europe.
This is much less of a problem in the cold winters of more continental climates
where harvests can take place on frozen soils.
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