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There has been a great deal of attention given to the “energy balance” of agricultural production, especially in relation to bio-fuel crops such as soybeans for bio-diesel, and corn for ethanol. The energy input considers obvious factors such as the amount of fuel used by agricultural equipment, but also includes the energy associated with the manufacture of inputs into the system such as fertilizers and crop protection products. Applying these methods to the cotton production system, to produce a typical cotton crop in the United States requires approximately 4900 MJ of energy, or in terms of the energy content in gallons of diesel fuel, 36 gallons.
Figure 1 shows the relative difference in total energy content in the typical mass of cottonseed produced per acre in the U.S. and total energy input. On the input side, what is not included is the solar energy captured by the plant, and this is why cotton production can have an energy “surplus”.
Figure 1 –Total energy input (excluding solar energy capture by the plant) to produce an acre of cotton compared to the total energy content of cottonseed on the same acre, expressed as the equivalent content of a gallon of diesel fuel.
The full energy of cottonseed has to be adjusted to account for its being processed into fuel. But, considering that potential for cottonseed energy is already twice the energy input, it is conservative to say that cotton can be energy self-sufficient. The oil alone from the seed can generate almost 20 gallons of bio-diesel per acre, and that does not take into account the energy content represented by other parts of the plant.
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