In terms of greenhouse gas emissions, scientific studies have long indicated the burning of fossil fuels and land-use changes such as deforestation have led to an increase in atmospheric concentrations of carbon dioxide since the beginning of the industrial revolution.
“Carbon dioxide atmospheric concentrations have risen from 280 parts per million prior to the industrial revolution to more than 400 parts per million today,” Owens said.
Carbon sequestration – the long-term capture and storage of carbon from the atmosphere, typically as carbon dioxide – is a method of reducing greenhouse gas emissions.
“Many different agricultural production practices can capitalize on carbon sequestration in both soil and biomass to reduce negative environmental effects,” Owens said. “These practices enable use of the natural carbon cycle to replenish carbon stores while reducing the amount of carbon in the atmosphere.”
That is where beef producers who employ grasslands as a pasture resource come in. Research by R.F. Follett and D.A. Reed published in 2010 examined the effects of grazing on soil organic carbon storage in North American rangelands. Follett and Reed found impacts ranging from no change to up to 268 pounds of carbon stored per acre per year.
“The variability in the impact grazing can have on carbon sequestration on rangelands, pastures and grasslands is due to differences in specific grazing management practices from operation to operation,” said Sara Place, assistant professor of sustainable beef cattle systems with OSU’s Division of Agricultural Sciences and Natural Resources.
The number of cattle grazed per acre, fertilization and prior land use can all affect how much carbon is stored.
“While changes in carbon sequestration due to grazing or other management decisions may be relatively minor on a per acre basis, they can translate into significant impacts if implemented on a large scale given the number of acres of grasslands in the world,” Place said.
Research by R. Lal published in 2011 indicated if soil organic carbon in agricultural ecosystems and grasslands could be increased 10 percent globally during the 21st century, the atmospheric concentration of carbon dioxide could be reduced by 100 parts per million.
“In addition to the potential for grazing to increase the capacity of soil carbon sequestration in certain cases, grazing beef cattle and other ruminants such as sheep and goats provide economic, societal and environmental value from available pasture and grassland resources,” Place said.
Pasture and grasslands account for approximately 27 percent of the land area in the United States. Avoiding the conversion of this land to tilled cropland and residential uses could help prevent further increases in greenhouse gas emissions.
Additionally, establishing permanent pastures for grazing beef cattle on degraded croplands that are currently tilled or of poor quality can sequester carbon at rates comparable to forests, according to a study released by the Council for Agricultural Sciences and Technology in 2011.
When it comes to beef production, the U.S. Environmental Protection Agency estimates direct emissions from the U.S. beef industry are only 1.9 percent of the total U.S. greenhouse gas emissions.
“Regardless of the beef production system, enhancing carbon sequestration through well-managed cattle grazing practices and improved feed production can reduce the carbon footprint of beef,” said Clint Rusk, head of the OSU Department of Animal Science.
Most beef cattle in the United States spend the majority of their lives on pastures and grasslands. For those finished in a feedlot, approximately 65 percent to 85 percent of their lives will be spent grazing. For grass-finished beef cattle, up to 100 percent of their lives may be spent grazing.
The main difference in carbon footprints between grass- and grain-finished beef occurs as a result of the time spent in the finishing phase, the type of feed consumed and the body weight of the animal at the end of the finishing phase.
“Cattle entering the final ‘finishing’ stage are typically 12 to 16 months of age, and remain in this phase until they achieve a level of body condition that will provide a positive eating experience for consumers,” Rusk said.
Average grass-finished cattle provide a live animal weight at harvest of 1,100 pounds, a dressing percentage of 58 percent and a carcass weight of 638 pounds per animal resulting in eight U.S. citizens being fed per animal, according to USDA per capita beef consumption data.
For grain-finished cattle with a live animal weight at harvest of 1,300 pounds, a dressing percentage of 64 percent and a carcass weight of 832 pounds per animal would result in 10.4 U.S. citizens being fed per animal, according to USDA per capita beef consumption data.
Rusk, Place and Owens stress it is important to remember that the Earth’s carbon cycle is a naturally occurring process and involves cyclical recycling, storage and use of a resource in different physical states.
Plants, animals including humans and soil microbes consume molecules containing carbon for energy and release some of the carbon back into the atmosphere as carbon dioxide through the process of aerobic respiration.
“As humans, our collective impact goes far beyond that,” Owens said. “Transportation and electricity production account for more than 56 percent of total greenhouse gas emissions in the United States. We should strive to do what we can to reduce emissions, and in agriculture most do, mainly because, as a whole, the responsibility of being stewards of the land is not lost on us.”
Environmentally sound, economically viable “best management practices” for beef production, crop production and other agricultural practices are available online at http://osufacts/okstate.edu via the OSU Extension fact sheet system.
“Developing and disseminating research-based information to help people solve concerns and issues of importance to them, their families and their communities is a fundamental aspect of our responsibilities as a land-grant university,” Owens said.