Agriculture Reference
In-Depth Information
Chapter 6
ENERGY USE EFFICIENCY IN BIOMASS
PRODUCTION SYSTEMS
Sanderine Nonhebel
1. INTRODUCTION
Over the last three decades, energy use efficiency (kg output /MJ input) in
Western agriculture has declined. This decline has been caused by an
increase in the number of inputs within agricultural systems. The decline in
efficiency observed in agriculture raises the question of what (from the
perspective of energy use) is the best system of growing energy crops. Is
this a high-input system with high yields per hectare, but with a low energy
use efficiency, or a low-input system with low yields per hectare but a high
energy use efficiency? Four short-rotation forestry production systems
(varying from high-input to low-input systems) will be evaluated with
respect to their resource use efficiency (in addition to fossil energy, solar
radiation and water will be taken into account.
Plant material is produced within various agricultural systems,
ranging from low-input systems in which hardly any external inputs are
used to high-input systems which require large quantities of external inputs
(fertilisers, pesticides, irrigation, etc.). In general, the yields in low-input
systems are much lower than in high-input systems. There is no
physiological difference between the production of plant material for food
and the production of plant material for energy. Sometimes the same crop
is even used for both purposes (rape seed, for instance). The major
difference between food crops and energy crops is that energy crops have
to yield energy. This implies that the energy that can be obtained from the
harvested plant material must be larger than the energy required to produce
the inputs. This condition does not hold for food crops: for several crops,
the fossil energy required to produce the crop is much higher than the
energy that can be obtained from it (
e.g.,
the production of tomatoes in
greenhouses). However, since food is not only consumed for the intake of
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