ENERGY USE EFFICIENCY IN BIOMASS PRODUCTION SYSTEMS - Economics of Sustainable Energy in Agriculture - page 76

between the production systems in resource use efficiency for land, solar
radiation and water are much larger (approximately 8 times) than the
differences in resource use efficiency for fossil energy (only twice as
large).
The system is efficient with respect to use of land, solar
radiation and water, but requires more fossil energy per ton of biomass
than the other systems. The more efficient use of land, sun and water in
comparison with the system can be explained by the fact that the
growing season is longer in Southern Europe. Due to the higher
temperatures in that region, the growing season covers the period between
March and November, while in the Netherlands, it does not start before
May. The longer growing season is the main reason for the higher yields
(for more details, see Nonhebel 1997). The crops in Southern Europe use a
larger part of the annual solar radiation and precipitation so that their
efficiency becomes higher. This high efficiency is the result of climatic
conditions, which implies that values found in one region cannot be
expected in other regions with other climates. The poor results of the
system in comparison with the system can also be explained by high
radiation and precipitation levels in Portugal (yields in both systems are the
same while inputs are higher).
4. DISCUSSION
The main purpose of this chapter is to quantify and give reasons for
varying input-output ratios in different production systems. For this
purpose, the yields chosen include the extremes in yields that may occur
within Europe. In order to calculate yields and inputs, assumptions are
made with respect to growing conditions and so on. The situation in
practice will deviate from the assumptions made here, which will lead to
other yields and other input requirements. Therefore, data obtained here
should not be interpreted as forecasts of input-output ratios for a biomass
crop at a specific location (when poplar is grown in Portugal, the actual
yields will be lower). Values found for yields and efficiencies should be
considered as orders of magnitude and differences should be evaluated in
terms of higher and lower and not as absolute values.
The systems chosen cover the whole range of current agricultural
practices: with and without use of fertilisers, irrigation or pesticides. The
yields cover the potentials attainable over Western Europe. Based on the
results found in this chapter, some general remarks can be made with
respect to the energy requirements for crops in different production
systems.