ARS Studies CO2 Levels

Published online: Sep 28, 2006
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Research is under way in the United States to discover how agriculture should respond if atmospheric carbon dioxide (CO2) concentrations double within the next century as some scientists predict.

Agricultural Research Service (ARS) scientists in Auburn, Alabama, are in the eighth year of the research, making it the world's oldest study comparing the effects of elevated and ambient levels of CO2 on different cropping systems.

Plant pathologist Brett Runion said preliminary results suggest that conservation management practices may enhance the benefits of elevated CO2 concentrations, such as larger plants and higher yields.

Results also show that elevated CO2 increases soil carbon, particularly when crops are grown with conservation management practices, despite greater amounts of CO2 going back to the atmosphere from the soil.

At the ARS Soil Dynamics Research Unit, scientists are examining how different management practices - such as conventional and conservation tillage - affect carbon storage. Their research will reveal some potential benefits and other consequences of increased CO2 concentrations and how we can influence them.

A series of cylindrical open-top field chambers, eight feet tall and 10 feet wide, exposes crops to varying levels of atmospheric CO2; soil and plant responses within these chambers are measured periodically.

"We want to understand how agricultural systems can best be managed to increase the amount of carbon stored in plant residues and soil," Runion said.

Increased carbon storage has multiple benefits, such as reduced soil erosion and compaction, increased water-holding capacity for plants, and slower rise in atmospheric CO2 concentration. Policymakers, action agencies, and businesses interested in trading carbon credits could use data from the study to make better decisions.

Runion is also using a system called ACES - for "automated carbon efflux system" - to track carbon as it flows from soil to atmosphere.

ACES is an open-flow system, so the pressure within its chambers does not build up and affect the CO2 levels. Unlike most measurement systems, which only allow for periodic assessments, ACES provides continual measurement of CO2 over the entire growing season.

Currently the research team is using ACES to compare the effects of CO2 on conventional and conservation tillage systems for a sorghum-soybean crop rotation.

Plant physiologist Stephen Prior said the research will help determine how much carbon can be stored in the soil under various management practices and which practices return more carbon to the atmosphere.

Currently, the group is using ACES to monitor CO2 coming out of soil for a sorghum-soybean rotation exposed to elevated or ambient levels of atmospheric CO2 and managed with either conventional or conservation practices.

Future plans include using the equipment to monitor other trace gases, such as methane and nitrous oxide, which are also suspected causes of global warming.