Agriculture Reference
In-Depth Information
% in 20 years owing to breeding efforts and management improvements.
The loss of leaves during winter may be preferable, since it leads to an
effective recycling of nutrients within the field.
Prolonging crop duration
Only from the fourth year after planting does
M
.
×
giganteus
reach its
maximum yield. In the first three years, yields are 0 %, 50 %, and 90 %,
respectively, of those of a full-grown crop (Ten Hag 1998). There is hardly
any long-lasting experience with
M.
×
giganteus.
The projected crop
duration is 10-15 years. Selecting those varieties that maintain their
productivity over a long time span may lead to higher average yields. If we
assume that in the next 20 years the crop duration will be prolonged from
10 to 15 years, the average crop yield would increase from 0.84 to 0.893
times that of a full-grown crop (calculated as [0+0.5+0.9+7
×
1] / 10 and
[0+0.5+0.9+12×1] / 15, respectively).
4. YIELD ESTIMATION AND DISCUSSION
In this section, the elements from the results section are combined to derive
yield estimates for
S. viminalis
and
M.
×
giganteus
in 2020. First, the
starting point will be defined by estimating current actual yields. The
calculations are illustrated in Figures 7.4a and 7.4b.
4.1 Current actual yield (year 2000)
At present only a few hectares of commercial
S. viminalis
and
M.
×
giganteus
are grown in the Netherlands, from which no yield data are
available. Therefore, it is assumed here that the present actual stem
production by
S. viminalis
and
M
.
×
giganteus
would be 72.5 % of the
optimal stem production. This is similar to the total above-ground yield in
winter wheat and silage maize, and thus equal 0.725 * 17.5 = 12.7 t d.m.
and 0.725 * 18.9 = 13.7 t d.m. respectively. During the
harvest operations, and in
M.
×
giganteus
also during winter, part of the
stem material is lost. Losses are estimated at 10 % in
S. viminalis,
and at 15
% in
M.
×
giganteus.
Therefore, the growth of harvestable stem biomass in
a full-grown crop is 0.9 * 12.7 = 11.4 t d.m.
in
S. viminalis,
and
0.85 * 13.7 = 11.6 t d.m.
in
M.
×
giganteus.
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