18 The Global Food System
Energy consumption by agriculture
A largely hidden cost of modern agriculture is the fossil fuel it must consume to
keep outputs high. Modern agriculture has tended to substitute external energy
sources for locally available ones. With the increasing use of nitrogen fertilizers,
pumped irrigation and mechanical power, which are all particularly energy inten-
sive, agriculture has become progressively less energy efficient. These three account
for more than 90 per cent of the total direct and indirect energy inputs to farming
in developing world countries (Leach, 1985, 1976). Mechanization reduces the
labour required for agriculture and so can cut variable costs if energy is cheap, as it
is in most industrialized countries. But for poorer countries, mechanization forces
increased foreign exchange expenditure on fuel, oil, engines and spares.
There have been many approaches to energy accounting for agricultural sys-
tems (Leach, 1976, 1985; Stout, 1979; Stanhill, 1979; Pimentel, 1980; Smil et al,
1982; Dovring, 1985; Pimentel et al, 1989; OECD/IEA, 1992; OECD, 1993).
These use such a variety of conventions that it is difficult to make direct compari-
sons. Some include only the direct fossil fuel energy consumed on farms; others
seek comprehensive energy balances by including all the indirect energy consumed
in manufacturing equipment and inputs, transporting produce to and from farms,
and the energy required to feed human and animal labour on the farm. Direct
energy represents what is immediately vulnerable to supply interruptions and so is
of more immediate interest to farmers. In general, apart from nitrogen fertilizers,
the manufacture of which is extremely energy intensive, direct energy costs far
exceed indirect costs (Leach, 1985).
With the greater use of machinery, fuel and nitrogen fertilizers in modern
high input agriculture, energy consumption is substantially greater than equiva-
lent low input or organic systems (Table 1.1). In the Philippines, for example, a
doubling of yields comes at the cost of an 8- to 30-fold increase in energy con-
sumption. In India, a 10–20 per cent increase in yields following mechanization
costs an extra 43–260 per cent in energy consumption. And in the US, high
input systems can consume 20–120 per cent more energy than low input sys-
tems, even though yields may be comparable. Larger farms also tend to use rela-
tively more energy than smaller ones. In the Punjab, farms in a class 14–25ha use
three times as much direct energy per hectare as farms smaller than 6ha (Singh
and Miglani, 1976).
Comparisons within countries or even regions are much more likely to be reli-
able than those between countries, as so many confounding factors become impor-
tant. However, a comparison of the energy consumption across systems is revealing,
if only at the level of orders of magnitude (Table 1.2). Low input, resource-con-
serving systems of production are much more energy efficient than the high input
systems typical of industrialized countries. Low input or organic rice in Bangla-
desh, China, and Latin America can produce 1.5–2.6kg cereal per MJ of direct
energy consumed. This is some 15–25 times more efficient than irrigated rice
produced in the US.