Converting forests or fields to biofuel crops can increase or decrease greenhouse gas emissions, depending on where and which biofuel crops are used, University of Illinois researchers report this month.
The researchers analyzed data from dozens of studies to determine how planting new biofuel crops can influence the carbon content of the soil. Their findings appear this month in the journal Global Change Biology Bioenergy.
Plants use the sun's energy to convert carbon dioxide from the atmosphere into the organic carbon that makes up leaves, stems and other plant parts. As plants decay, this carbon goes into the soil. Organic carbon is an important component of soil health and also influences atmospheric carbon dioxide levels. Whenever the soil is disturbed, as occurs when land is plowed or cleared of vegetation, some of this carbon returns to the atmosphere in the form of carbon dioxide.
"From the time that John Deere invented the steel plow, which made it possible to break the prairie sod and begin farming this part of the world, the application of row crop agriculture to the Midwest has caused a reduction of soil carbon of about 50 percent," said Evan DeLucia, a professor of plant biology at Illinois and corresponding author on the new study.
Any debate on the environmental consequences of using plants to produce liquid fuels should also consider how each option affects soil carbon, DeLucia said.
"The biggest terrestrial pool of carbon is in the soil. The top meter of soil holds more than three times the amount of carbon stored in either vegetation or the atmosphere, so if you do little things to change the amount of carbon in the soil it has a huge impact on the atmosphere and thus global warming."
Unlike corn, which must be replanted every year, perennial grasses such as switchgrass and Miscanthus preserve and increase carbon stores in the soil. These and other grasses have been proposed
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University of Illinois at Urbana-Champaign