The Energetics of Agroecosystems - Agroecology: The Ecology of Sustainable Food Systems - page 263

Current trends indicate that fossil fuel use in agricul-
ture will continue to increase to meet growing production
needs (Pimentel and Pimentel, 1997), resulting in more
rapid depletion of world petroleum reserves, and com-
petition with other uses for fossil fuels.

Off the farm, the wind and water erosion of soil asso-
ciated with mechanized agriculture has had negative
impacts on other systems, especially downstream. Recent
work on gaseous emissions from nitrogenous fertilizers
(N 2 O and NO) has shown that the addition of these mate-
rials to the atmosphere is beginning to impact the global
nitrogen cycle, further damage the ozone layer, and exac-
erbate the global warming problem. The simplification of
farming systems, which always accompanies high indus-
trial energy inputs to agriculture, is causing greater loss
of regional biodiversity.
From an economic and social perspective, the prob-
lems with excessive dependence on fossil fuel energy in
agriculture go much beyond the issue of the efficiency of
return on investment for the energy that is used. Depen-
dence on fossil fuel use means greater vulnerability to
changes in the price and supply of petroleum. As was seen
in the oil crisis of 1973, and then periodically since then,
petroleum prices can suddenly rise, increasing the costs
of agricultural production. With fossil fuel consumption
continuing to rise worldwide, the risks to fossil fuel-based
agriculture become even greater. The problem will
become even more critical as developing countries are
forced to intensify their own agricultural output to meet
the growing demand for food.
A final problem with fossil fuel-based agriculture is that
it is linked to a certain kind of agricultural development: it
enables large-scale, mechanized agriculture, which all over
the world is displacing traditional agriculture and thus
forcing migration to cities, disrupting cultural ties, and
undermining self-reliance.

TOWARD SUSTAINABLE USE OF ENERGY IN
AGROECOSYSTEMS

Examining conventional agriculture through the lens of
energy reveals a critical source of unsustainability. Con-
ventional agriculture is today using more energy to pro-
duce, process, transport, and market food than the food
itself contains, and most of this invested energy comes
from sources with a finite supply. We have come to depend
on fossil fuels to produce our food, yet fossil fuels will
not always be available in abundant supply. Moreover,
dependence on fossil fuel use in agriculture is linked with
virtually every other source of unsustainability in our food
production systems.

P ROBLEMS WITH I NTENSIVE F OSSIL F UEL U SE

Growing levels of energy inputs to agriculture have played
an important role in increasing yield levels in many of the
world's agricultural ecosystems over the past several
decades. However, as described above, most of these
energy inputs come from industrial sources, and most are
based on the use of fossil fuels. If the strategy for meeting
the food demands of the growing population of the world
continues to depend on these sources, several critical prob-
lems will begin to emerge. Some of these problems are
ecological, but others are economic and social.
As has been noted throughout the chapters of this topic,
when ecological processes are ignored, environmental
degradation begins to appear in the agroecosystem. The use
of intensive cultural energy inputs is what has permitted us
to ignore ecological processes. The application of inorganic
fertilizers masks declines in soil fertility; pesticides contrib-
ute to and hide declines in agricultural biodiversity.
However, the consequences of ignoring ecological
processes are now becoming more evident. At the farm
level, a shift to heavy mechanization and high use of fossil
fuel-derived chemical inputs have led to problems of
organic matter loss, nutrient leaching, soil degradation,
and increased soil erosion. Water supplies have become
polluted, and excessive pumping of the ground water has
led to exhaustion of aquifers and accompanying water
shortages. Pests and diseases have developed resistance to
inundative use of pesticides, and pesticides have contami-
nated both farm environments and natural ecosystems,
causing health problems for farmers and farm workers and
destroying populations of beneficial insects and micro-
organisms.

FUTURE ENERGY DIRECTIONS

Clearly, sustainable food production depends to a large
extent on more efficient use of energy, as well as less
reliance on industrial cultural energy inputs and fossil
fuels in particular. As suggested in this chapter, a key to
more sustainable use of energy in agriculture lies in
expanding the use of biological cultural energy. Biological
inputs are not only renewable, they have the advantages
of being locally available and locally controlled, environ-
mentally benign, and able to contribute to the ecological
soundness of agroecosystems. Also important is the con-
version to alternative energy sources and appropriate tech-
nologies that lessen dependence on fossil fuel.
Many agroecosystems currently in use point the way
toward the future. The typical organic farming system, in
which animals and legumes replace some of the fossil fuel-
derived inputs, consumes 28 to 32% less energy than an
equivalent conventional system (Pimentel et al., 2005).
A Danish study found that a grass-clover integrated
organic dairy farm was able to reduce total energy use
37.5% over its conventional counterpart, and systems