Environmental Engineering Reference
In-Depth Information
uniformity of energy subsidies in livestock production
and clearly invalidate any simplistic perception of seafood
as a particularly attractive energy bargain. Fishing is, after
all, just intensive hunting, and it requires less energy to
capture the more abundant but also less sought-after spe-
cies (octopuses, krill). But even this generalization breaks
down in the regions of chronic overfishing (Mediterra-
nean) or after sudden environmental changes (El Ni˜o's
effect on Peruvian anchovetta). The same is true of
aquaculture. The best efficiencies come with polycultures
based on herbivorous species, particularly East Asian
carp. As little as 150-200 kJ/g may be needed to pro-
duce 1 g of carp protein; aquacultured salmon needs
only 100 kJ/g, but most of its feed must be of animal or-
igin, including a significant share of fish oil.
10.5 Modern Food System: Gains, Costs,
Efficiencies
The overall magnitude of agricultural energy subsidies
is insignificant compared to the input of solar energy.
While an intensively cultivated cornfield in Iowa may re-
ceive annually 30 GJ/ha in direct and indirect energy
subsidies, solar energy that reaches it during the 150
days between planting and harvesting amounts to 30
TJ/ha, a 1,000-fold difference (Smil, Nachman, and
Long 1983). The enormous solar flux is free. The costly
flows of fossil fuels and electricity are limited, but without
them productivity would be a fraction of the subsidized
harvest even with maximum in put of animal labor. This
productivity gain has not only sustained historically un-
precedented population growth but also improved the
quality of nutrition. Between 1900, when energy subsi-
dies were limited to low-level fertilization and rudimen-
tary mechanization in industrializing nations, and 2000,
the world's cultivated area grew by 80%-100% (Golde-
10.12 The world's cultivated area, aggregate crop harvests,
and energy subsidies in modern agriculture, 1900-2000.
From Smil (2000b).
wijk 2001), but the energy harvested in edible crops
expanded sixfold. This greater average productivity was
made possible by an 85-fold increase in energy subsidies
per harvested hectare (fig. 10.12).
In 1900 1 ha of cultivated land could feed just 1.5
people, and the edible harvest (before storage and distri-
bution losses) prorated to less than 10 MJ/day per cap-
ita. This rate offered only a slim food supply margin
above the average daily requirement of about 9 MJ/day
per capita. Moreover, prevailing diets were composed
of just a few staples, and the relatively low crop yields
greatly limited the extent of animal feeding and hence
