ENERGY USE EFFICIENCY IN BIOMASS PRODUCTION SYSTEMS - Economics of Sustainable Energy in Agriculture - page 71

energy but also for its nutritional value (vitamins etc.), the value of the
harvested material is not determined by its heating value only.
During the last decade, several studies have been done on the use
of fossil energy in food crop production systems. These studies have been
conducted at various levels of scale (comparison of organic agriculture to
high-input agriculture; developments in agriculture over the last 50 years,
or between countries (Naylor 1996; Kramer et al. 1999; Schroll 1994;
Conforti and Giampietro 1997). All authors have come to the conclusion
that fossil energy is used most efficiently in the low-input crop production
systems.
Since there are no physiological differences between the crops, the
input-output relationship for food crops can also be expected for energy
crops. This would imply that fossil energy use efficiency of low-input
energy crop systems is higher than the energy use efficiency in high-input
crop systems. When efficient use of fossil fuels is of importance, energy
crops should be grown in so-called low-input systems. However, the
studies done by Uhlin (1998; 1999) on the overall (fossil and solar) energy
use efficiency of the Swedish agricultural system show that overall, energy
use efficiency has increased over the last three decades instead of declined.
According to these results, high-input energy crop systems use energy
more efficiently.
Based on the existing information on food crops, no conclusions
can be drawn with respect to the consequences of choice of a particular
production system on anticipated yields. This chapter examines in detail
the input-output ratios within four biomass production systems. For all
systems, the energy use efficiency is calculated and any differences found
between the systems are explained. Finally, the results are compared with
previous studies on energy efficiency of food production systems.
2. MATERIAL AND METHODS
In order to determine the efficiency of resource use, information on inputs
and outputs (yield) is required. For food producing systems, this
information (at various levels of scale) can be obtained from agricultural
statistics (KWIN; FAO; LEI). These kinds of data were used in the food
studies mentioned earlier. For energy crops, this type of data is lacking,
since these crops are presently grown in only a limited number of
experimental situations.
The method used here is a different one: the target-oriented
approach derived from ecological production research (van Ittersum and
Rabbinge 1997). In this approach, the yield level (the output) is defined