From danamex@mail.internet.com.mx Fri May 19 16:21:19 2000 Date: Fri, 19 May 2000 14:17:05 -0500 From: Ronald Nigh To: sanet-mg@ces.ncsu.edu Subject: Re energy accounting [ The following text is in the "iso-8859-1" character set. ] [ Your display is set for the "US-ASCII" character set. ] [ Some characters may be displayed incorrectly. ] 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 To Unsubscribe: Email majordomo@cals.ncsu.edu with the command "unsubscribe sanet-mg". If you receive the digest format, use the command "unsubscribe sanet-mg-digest". To Subscribe to Digest: Email majordomo@cals.ncsu.edu with the command "subscribe sanet-mg-digest". All messages to sanet-mg are archived at: http://www.sare.org/san/htdocs/hypermail