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The Simple Physics of Energy Use$
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Peter Rez

Print publication date: 2017

Print ISBN-13: 9780198802297

Published to Oxford Scholarship Online: December 2017

DOI: 10.1093/oso/9780198802297.001.0001

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Agriculture—Things That Are Grown

Agriculture—Things That Are Grown

(p.205) 13 Agriculture—Things That Are Grown
The Simple Physics of Energy Use

Peter Rez

Oxford University Press

Timber has the lowest embodied energy of any of the construction materials. Paper production from trees requires much more energy. There is some energy saving in recycling, as recycled paper substitutes for pulp derived from wood chips. Growing crops for food also requires energy. The energy required for plants to grow comes from the sun, but there are additional energy inputs from fertiliser and farm machinery to speed up the growth process and vastly improve crop yields. If grains are used as animal feed, then the energy inputs are much larger than the dietary energy output—the larger the animal and the longer it is fattened up before slaughter, the more inefficient the process. The use of crops to make fuel for electrical power generation or for processing into liquid fuels is horribly inefficient. The problem is simple—the plants do not grow fast enough!

Keywords:   timber, paper, pulp, kraft process, pig, cow, chicken, rice, wheat, corn, Haber–Bosch, fertiliser, biofuel, bread

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