YIELD INCREASES OF THE BIOMASS CROPS SALIX VIMINALIS AND MISCANTHUS GIGANTEUS: A LOOK TO THE FUTURE - Economics of Sustainable Energy in Agriculture - page 94

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to 12.0 t d.m. in 20 years, implying an annual increase rate of 1.2
%. If the crop duration of M. × giganteus could be increased to 15 years,
the average stem yield in spring 2021 would be 0.893 * 14.5 = 13.0 t d.m.
All developments together cause an increase in stem growth from 9.8 t
d.m. to 13.0 t d.m. in 20 years, corresponding with an
annual increase rate of 1.41 %. The order of magnitude of the annual
increase rate calculated in this study corresponds with the one estimated by
Hall et al. (1993) and Faaij (1997). However, it should be noted that the
time span over which Hall et al. (1993) expect an average annual increase
by 1.2-1.6 % is longer than the 20 years' period considered here, and the
absolute yield level predicted by Faaij (1997) is higher than the one
estimated here. This implies that the expectations for future yield
development in this study are lower than those by Hall et al. (1993) and
Faaij (1997). The other studies summarized in Table 7.1 present estimates
for yield increases in biomass crops that are high compared to the ones
calculated in this study. The more modest estimates given here seem more
realistic, the more so as considerations of long-term sustainability may
limit maximum yields, as argued by Hall et al. (1993). Taking into account
the use of energy and water, and the effects of fertilizers and pesticides on
the environment, aiming at maximum yields may not necessarily be the
most sustainable way to produce energy from biomass crops.
ACKNOWLEDGEMENTS
I am grateful to S. Larsson, J. Goudriaan, S.K. Mertens and the late D.O. Hall for valuable
comments on an earlier draft of the manuscript. The study was funded by the Dutch
National Research Programme on Global Air Pollution and Climate Change (Project code
953233).
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