Madison, Wisconsin
January 13, 2009
Global yields of most biofuels
crops, including corn, rapeseed and wheat, have been
overestimated by 100 to 150 percent or more, suggesting many
countries need to reset their expectations of agricultural
biofuels to a more realistic level.
That's according to a study, led by Matt Johnston and Tracey
Holloway of the University of
Wisconsin-Madison Nelson Institute for Environmental Studies
and Jon Foley of University of Minnesota, that drew on actual
agricultural data from nearly 240 countries to calculate the
potential yields of 20 different biofuels worldwide.
The analysis, publishing today (Jan. 13) in the open-access
journal Environmental
Research Letters, indicates the biofuels production
potential in both developing and developed countries has often
been exaggerated. Why? Because current yield estimates, most of
which are based on data from the United States and Europe, don't
account for local differences in climate, soils, technology and
other factors that influence agricultural outputs.
By offering an analysis of detailed, regional yield data that do
encompass this variability, the scientists hope to empower wiser
choices by countries about whether to invest in ethanol or
biodiesel, which crops to plant, and how best to use existing
farmlands. Although agricultural biofuels have been sharply
criticized for their impacts on the environment and food supply,
the reality is they're here to stay, say the researchers, at
least until alternatives such as cellulosic ethanol are
developed. And that makes the availability of sound information
critical.
"The biofuels industry has grown at an incredible rate. It's a
multibillion-dollar industry now," says Johnston, a graduate
student in the Nelson Institute's Center for Sustainability and
the Global Environment (SAGE). "So what we've tried to do is
move beyond the back-of-the-envelope calculation - the time for
that is over. We need to look at better data sources and make
more informed decisions."
In the past, he explains, policymakers, companies and farmers
have based decisions about biofuels in part on "yield tables,"
which make simple side-by-side comparisons of the fuel yield per
unit of land for various crops; for example, the amount of
ethanol a hectare of sugarcane will generate versus a hectare of
corn.
The problem with these widely quoted tables, says Johnston, is
the original sources of the numbers usually aren't cited, making
it impossible to gauge their validity. What's more, the tables
typically select a single value - often from just one country or
even a single farm - to represent the yield of each crop
regardless of where it's grown.
"Often these are very optimistic numbers and they're chosen to
promote biofuels," says Johnston. "So they usually (represent)
the highest-yield, best-case scenario."
To take a more sober look, Johnston turned to a global
agricultural database, developed at SAGE, which provides actual
yields of 175 crops, circa the year 2000, at a resolution of
roughly five miles by five miles across the entire globe. After
tapping it for yields of 10 biodiesel crops, such as soybean,
rapeseed and oil palm, and 10 ethanol feedstocks, including
corn, rice and wheat, Johnston calculated and mapped the amount
of biofuel that could be produced per hectare in every possible
country by crop combination - some 3,000 in all.
To evaluate his numbers against published yield table values, he
then computed a global average yield for each of the 20 fuels,
as well as the average yields of each in both developed and
developing nations as a whole.
What he found were large gaps between the yield table numbers
and his own, especially for developing countries. For instance,
while his calculation for the average yield of corn ethanol in
developed countries matched well with current yield table
estimates, the average yield of developing countries was nearly
100 percent lower.
Such disparities weren't restricted to the developing world
either. Canada, for example, is one of the world's largest
producers of rapeseed. Yet, Johnston calculated its average
yield of rapeseed biodiesel at just 550 liters per hectare -
nearly half the estimates in yield tables, and well below the
average for other developed nations.
Researchers at SAGE and University of Minnesota plan next to
compare yields of biofuels in areas with similar climates, and
then study how differences in management practices, such as
irrigation or fertilizer use, may be contributing to gaps in
production. The idea is to help countries get the most from
existing farmlands, so they'll put less new land to the plow and
can better balance investment in biofuels against other needs,
such as food security. But first they just need better data.
"This is not a one-dimensional issue and just knowing the crop
yields isn't going to tell you what the best solution is," says
Holloway. "But if you're going to be making land use decisions
related to biofuels, it's critical that you at least know what
you're going to get from a plot of land."
All data from the study can be acquired from SAGE at
http://www.sage.wisc.edu/energy/index.html. The paper's
other authors are Chris Kucharik, SAGE, and Chad Monfreda,
Arizona State University. |
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