Agriculture Reference
In-Depth Information
The amount of oil and fat projected to be available for conversion to energy will pro-
duce possibly 2 billion gallons of biodiesel. These are significant quantities of fuel,
and their production is economically important. However, to replace the energy in
the 140 billion gallons of gasoline and the 40 billion gallons of diesel fuel currently
used for ground transportation in the United States with biofuel would require nearly
200 billion gallons of ethanol and 50 billion gallons of biodiesel. Therefore, for bio-
fuel to replace fossil transportation fuel, very large quantities of biomass feedstock
must be made available, and technologies for conversion of these feedstocks must be
commercialized.
A joint USDA-DOE (U.S. Department of Agriculture/Department of Energy)
study concluded that, “The land resources of the United States are capable of
producing a sustainable supply of biomass sufficient to displace 30% or more of
the country's present petroleum consumption” (Perlack et al., 2005). The study
estimated that agriculture could provide nearly a billion dry tons of cellulosic
biomass annually, and that forestry resources could add in excess of 0.3 billion
additional dry tons. This is less than 1% of the biomass of the earth's biosphere
produced for human use and consumption as estimated by Whittaker and Likens
(1975) (Table 17.1). At a conversion efficiency of 100 gallons of ethanol per dry ton,
1.3 billion tons of biomass would yield in excess of 130 billion gallons of liquid
fuel. Based on energy content, approximately 100 billion of the current 180 bil-
lion gallons of liquid petroleum transportation fuel now consumed as gasoline and
diesel fuel in the United States could be replaced. Obviously, future demand for
transportation fuel will depend on changes in miles driven and in vehicle fuel use
efficiency. If the fuel economy of all vehicles was increased by 30%, an amount
similar to the mandate for cars and light trucks recently approved by the U.S.
Congress, it is reasonable to project that biofuels could provide all of the highway
transportation fuel now used. To reach this point, the biofuel industry must grow
significantly, a growth that will require enacting governmental policies to pro-
vide incentives and mandates and will also require development of technology to
improve biofuel production.
Opinions differ on changes in land use and in production practices that would be
required for agriculture and forestry to provide significant amounts of bioenergy.
Changes will by necessity occur. The challenge is to ensure that land use changes
made and production practices adopted are sustainable such that the country and the
world move toward a sustainable, renewable energy future.
On a global basis, the energy content of biomass produced by photosynthesis
is greater than the energy that human activities consume. Therefore, from purely
an energy content perspective, bioenergy can meet the world's energy needs.
However, biomass must also provide adequate food, feed, and fiber as well as the
ecological needs of the planet's forests, grasslands, marshes, and so on. For this
to be realistic, it must be possible to efficiently and sustainably collect and make
this energy available economically in the form and quantities and at the times
needed. In addition, all other needs for biomass must be sustainably met. This no
simple task.
