Dear SANET,
The energy accounting model pioneered by Odum is reductionist to the point
of not really being very useful. Not only does it reduce agricultural
production to the single dimension of energy flow, as I mentioned in my
precious post, but even the concept of energy utilized is reductionist and
misleading.
The classic biogenergetic model used by Odum is based on the definition of
the energetic value of a substance as the total combustible calories
(joules). In other words, the energy value of a kilogram of corn is
determined by burning the corn and seeing how much the heat generated will
raise the temperature of water. A liter of gasoline is subjected to the
same treatment. The energetic value of human labor is calculated in terms
of metabolic energy spent in physical work but is ultimately based on the
same idea of 'energy content' of carbohydrates. Then, rather simplistic
ratios of, say kcal of gasoline (and other inputs whose 'energy value' is
similarly defined) to kcal of corn are used to define the 'efficiency' of
corn production, etc. Such figures may be milding interesting (as is the
Pimentel et al. 1973 article cited previously) but as a meaningful measure
of anything having to do with sustainability, or even the bioenergetic
aspects of agriculture, I think it's pretty irrelevant.
What is interesting about energy in biological system are the structures in
which it is captured. New concepts of bioenergetics in molecular biology
have more to do with the movement of specific molecules across membranes or
the changes in molecular structure as small quanta of energy are shifted
from one kind of chemical bond to another. Essential amino acids, for
example, have interesting bioenergetic properties that nonessential ones do
not. Same for fatty acids. Yet the caloric value of all the amino acids
measured in terms of how much heat they generate on combustion is about the
same. In other words, the classic energy accounting approach is two clumsy
to really get at issues of quality in biological systems.
These comments jive with Dale's more general comment: "Different forms of
energy (tractor vs fuel vs produce) have different environmental and
economic values and impacts that cannot be
captured in megajoules"
We need instruments of much finer resolution to get at the biological and
ecological processes underlying sustainable agriculture.
Ronald Nigh
Dana, A.C.
Mexico, D.F. & San Cristóbal de Las Casas, Chiapas
Tel. y FAX 525-666-73-66 (DF)
529-678-72-15 (Chiapas)
danamex@mail.internet.com.mx
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