Appendix B. The Energy Index

Most of the energy in organic residues is associated with the carbon. It is released when the carbon is oxidized:

C + 2O → CO2 + energy

This energy amounts to about 370 BTU/mole of carbon (The heat of formation of CO2 is -94,000 gram calories/mole, and each BTU of energy is equivalent to 252 gram calories).

The organic component of residues is approximately half carbon. Since a ton is equal to 2000 lbs, each 1% of organic matter is equivalent to 10 lbs of carbon per ton of residues. One pound is equal to 454 grams. The formula weight of carbon is 12, so 10 lbs of carbon is 4540 grams, or 4540/12 = 378 moles of carbon. Thus the energy from the carbon in each 1% of organic matter contains (378 moles) X (370 BTU/mole), or about 140,000 BTU per ton of residues. This is also the energy in one gallon of #2 heating oil. So each 1% of organic matter in organic residues contains the same energy as one gallon of heating oil/ton of residue.

Humus contains about 58% carbon, more than the organic matter of fresh residues. Consequently each 1% of humus contains as much energy as about 1.2 gallons of fuel oil/ton of soil. One acre of soil of thickness about 6 - 8 inches (a plowdepth layer) weighs about 1000 tons. Hence the energy in each 1% of humus in a plowdepth layer contains as much energy as about 1200 gallons of fuel oil/acre.

© 2013 Robert Parnes

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