One Answer For Cleaner Air, Water: Better Agricultural Practices
COLUMBUS, Ohio - Better management of agricultural lands in the United States could help reclaim the 100 to 300 million tons of carbon that escapes into the atmosphere each year, according to a researcher at Ohio State University.
Carbon is considered one of the key pollutants contributing to global warming.
Agricultural lands, which include crop, pasture and grazing lands, comprise about 42 percent of the total landmass of the United States. In the last 200 years, nearly 5 billion metric tons of carbon has been released into the atmosphere because of land use change, such as plowing, drainage and residue removal in the U.S., said Rattan Lal, a professor of natural resources at Ohio State. Each year, accelerated soil erosion releases about 15 million metric tons of carbon into the atmosphere in the United States alone.
"It's far easier in the short run to change land management practices in order to reduce carbon emissions than it is to reclaim carbon from fossil fuels, Lal said."
"Soil can either be a source of, or a sink for carbon - it can either emit carbon or take it in," he said. "We need to start practicing ways to take it in. And we can do that by changing how we manage the land."
Lal presented his findings with John Kimble and Ronald Follett, both with the United States Department of Agriculture, on December 18 at the American Geophysical Union meeting in San Francisco.
"Agricultural land has the potential to sequester carbon while improving the quality of soil and the environment," Lal said. His suggestions for improving carbon sequestration in agricultural lands include:Converting traditional plowing practices to conservation tillage Growing cover crops during the winter, such as alfalfa and hay Protecting marginal land (such as steep slopes) under the Conservation Reserve Program (CRP), a program that gives farmers financial incentive to set aside land unfit for agricultural use Planting vegetation with deeper roots in order to control erosion Controlling the grazing of cattle on the land - that is, limiting grazing to a certain portion of the land Restoring degraded lands through planting and grazing management Taking into consideration landscape type. For example, steep slopes shouldn't be cleared - doing so would only contribute to erosion
Draining and plowing both strip soil of its carbon content. But there are ways to turn soil into a carbon sink. In agricultural practices - and depending on the soil type - farmers could implement either no-till farming or crop rotation practices to reduce erosion. No-till farming means a farmer doesn't plow his fields between growing seasons.
The 5 billion tons of carbon lost to the atmosphere because of land mismanagement may seem like a drop in the bucket compared to the worldwide estimate of 260 billion tons of carbon emitted in the last two centuries from fossil fuel combustion. But worldwide, carbon emission from soil accounts for about one-third (60 to 90 billion tons) of the amount emitted by fossil fuels. Creating soil sinks for carbon would buy researchers time to figure out what to do about fossil fuels, which accelerate global warming, Lal said.
"Putting carbon back in the soil is truly a win-win situation," Lal said. "Carbon filters impurities from water and it also enriches soil (carbon-poor soil requires more fertilizers to produce the same yield as carbon-rich soil). More carbon sequestered in the soil means less erosion and, of course, less emission to the atmosphere."
Researchers have estimated the amount of carbon lost from soil during the last 200 years by comparing carbon amounts in the soil of undisturbed, forested areas to amounts in land that had been cleared for pasture or agriculture. "The difference in carbon content between the two is about 10 to 20 tons per acre," Lal said. "Adding that up state-by-state and country-by-country means a pretty significant amount of carbon has gone into the atmosphere."
It's far easier in the short run to change land management practices in order to reduce carbon emissions than it is to reclaim carbon from fossil fuels, Lal said.
"It's a question of how to put carbon back into the soil," he said. "It isn't as economical or effective to retrieve the carbon that has been taken from fossil fuel as it is to replenish the carbon in soil.
"But sequestering carbon in soil is only a short-term solution," Lal said. "Soil has a finite capacity to hold carbon. If these practices were adopted today, the 'sink' would be full in 25 to 50 years."
Lal's work is funded by the U.S. Department of Agriculture; the Natural Resources Conservation Service; the Department of Energy; American Electric Power; and Battelle Pacific.#