The Energetics of Agroecosystems - Agroecology: The Ecology of Sustainable Food Systems - page 261

FIGURE 18.8 Oxen-drawn plow cultivating a field for corn planting near Cuenca, Ecuador. Most of the energy in this system
is from renewable local sources.

Production
of seeds
4.8%

Electricity
1.1%
Transportation
1.0%

Drying
7.4%

Production
of
equipment
5.4%

Human
labor
25.6%

Insecticides &
herbicides
6.7%

Machinery
11.4%

Irrigation
7.4%

Energy content of harvest:
3,340,550 kcal/ha

Gasoline & Diesel
14.0%

Ox labor
64.3%

Seeds
5.8%

Labor
0.1%

Total cultural energy input: 770,253 kcal/ha

Phosphorus,
potassium, limestone
9.5%

FIGURE 18.9 Cultural energy inputs into a traditional corn
production system using animal labor. The ratio of the food
energy output to the cultural energy input for this system is
4.34:1. The energy in the cover crop and fallow plants that were
incorporated into the soil is not included in the calculations.
Animal manures returned to the soil are included in the energy
input from the oxen. (Data from Cox, G. W. and M. D. Atkins.
1979. Agricultural Ecology . Freeman: San Francisco.; Pimentel,
D. and M. Pimentel (eds.), 1997. Food, Energy, and Society.
2nd ed. University Press of Colorado: Niwot, Colorado.)

Nitrogen fertilizer
35.7%

FIGURE 18.10 Components of the 10,535,650 kcal/ha of
cultural energy used for corn production in the U.S. To t al
grain yield averages 7500 kg/ha and the kcal output-to-input ratio
is 2.5:1 (Data from Pimentel, D. and W. Dazhong 1990. Tech-
nological changes in energy use in U.S. agricultural production.
In Carroll, C.R., J.H. Vandermeer, and P.M. Rosset (eds.). Agro-
ecology McGraw-Hill: New York.)