The Energetics of Agroecosystems - Agroecology: The Ecology of Sustainable Food Systems - page 259

Energy input Energy output

Natural
ecosystem

Shifting
cultivation

Non-mechanized
permanent farming

Modern mechanized
agriculture

Ecological energy
Cultural energy
Biological cultural energy
Industrial cultural energy

FIGURE 18.6 Approximate relative size of energy inputs
and outputs in four types of systems. The actual size of the
ecological energy input for each system is much larger than
shown. Note that for modern mechanized agriculture, the total
energy output is smaller than the input of cultural energy; this
disparity is often more extreme than shown.

their by-products, and any human-directed biological
activity or by-product. Some of the different forms of
biological cultural energy, with their approximate energy
values, are presented in Table 18.2.
Biological cultural energy is renewable in that it
derives from food energy, the ultimate source of which is
solar energy. Biological cultural energy is also efficient in
facilitating the production of harvestable biomass. As we
saw above, agroecosystems that rely mainly on biological
cultural energy are able to obtain the most favorable ratios
of energy output to input.
Human labor has been the key cultural energy input
to agriculture ever since its beginning, and in many parts
of the world today it continues to be the primary energy
input, along with animal labor. In shifting cultivation sys-
tems, for example, human labor is practically the only
form of energy added other than the energy captured
through photosynthesis. These systems' high ratios of
food energy produced to cultural energy invested, ranging
from 10:1 to 40:1, is a reflection of how efficiently human
labor can direct the conversion of solar energy into har-
vestable material (Rappaport 1971; Pimentel and Pimentel,
1997). As an example, the energy budget for a traditional
shifting cultivation or swidden corn crop in Mexico is
shown in Figure 18.7.
Many other types of traditional, nonmechanized food
production systems, where biological cultural energy is the
primary input, realize a very favorable return on their
investment of cultural energy. In pastoral agroecosystems,
in which herding and animal care are the main human
activities, and animals gain their food energy from natural
vegetation, the ratios of food energy produced to cultural
energy invested range from 3:1 to 10:1. Even intensive,
nonmechanized farming systems maintain a positive energy
budget. Paddy rice production systems in parts of Southeast

FIGURE 18.5 Coffee grown under the shade of native trees
in Veracruz, Mexico. In this agroecosystem, coffee is substituted
for understory species without major alteration of the upper can-
opy of native trees. Because the natural ecosystem is altered so
little, only small inputs of cultural energy are required to maintain
the productivity of the system.

goal is to also increase the level of solar energy capture
(productivity) above that shown by the previous natural
system, the levels of cultural energy required can be very
high (Figure 18.5).
Figure 18.6 offers another perspective on the relative
energy costs and energy benefits of different types of
agroecosystems. Although using a large amount of cul-
tural energy enables conventional agroecosystems to be
more productive than others, such systems are not realiz-
ing a good return on their energy investment. Food pro-
duction that is more energy efficient is possible if we
decrease inputs of industrial cultural energy, increase the
investment of biological cultural energy, and change how
industrial cultural energy is used.

U SE OF B IOLOGICAL C ULTURAL E NERGY

Biological cultural energy is any energy input with a
biological source under human control — this includes
human labor, the labor of human-directed animals and