Agriculture Reference
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dependent on model assumptions concerning leaf mortality. Simulations
showed that in the Netherlands stem growth under optimal conditions
would increase to 21.0 t d.m. if the existing allocation pattern
could be changed to the optimal one. There may be biological restrictions
to reaching the simulated optimal pattern of dry matter partitioning
completely, but the order of magnitude of the increase is such that breeding
in this direction seems promising.
Prolonging crop duration and cutting cycle
In the year of planting, stem growth is negligible, and in the year after
planting it reaches about 50 % of the growth of a full-grown crop. In the
year after harvest, growth is reduced by about 50 % compared to the later
years of the cutting cycle. Currently, a crop duration of 20 years and a
cutting cycle length of 4 years is usual, so that the average stem growth is
0.825 times that of a full-grown crop (calculated as [0+0.5+1+1 +
4×(0.5+1+1+1)] / 20). Selecting for varieties that maintain a high
production level both during the cutting cycle and during the life-time of
the crop may lead to a higher average stem production. If we assume that
in the next 20 years the crop duration can be prolonged to 30 years, and the
cutting cycle length to 5 years, which are the maximum values reported to
date, the average stem growth in 2020 will be 0.867 that of a full-grown
crop (calculated as [0+0.5+1+1+1 + 5×(0.5+1+1+1+1)] / 30). In making
estimates for crop duration and cutting cycle length, there are two
qualifications that should be considered. First, mechanical harvesting
techniques set a limit to the size of the stems that can be harvested and thus
to the length of the cutting cycle. Second, when new higher-yielding
varieties are introduced, farmers may prefer replacement of the existing
crop by a new one, and not extend the duration of the current crop.
3.2.2 Miscanthus
×
giganteus
Partitioning
Results for
M.
×
giganteus
were largely similar to those for
S. viminalis.
Simulations for the Netherlands over the period 1968-1997 showed that the
potential stem biomass production of a full-grown
M.
×
giganteus
crop is
18.9 t d.m.
and that it may be increased to 23.1 t d.m.
by
optimal partitioning.
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