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Less is more: No-till agriculture helps mitigate global warming

No-till agriculture helps soil retain carbon.
Click here for a high resolution photograph.

Using research, technology and tractors, farmers around the world are plotting and carrying out a small revolution-a revolution that has the potential to transform agriculture and use it as a tool to mitigate global warming.

The concentration of greenhouse gases—mainly carbon dioxide, CO2—is increasing in the atmosphere at unprecedented levels. No-till agriculture offers one way of slowing further increases in atmospheric CO2.

No-till agriculture produces crop yields similar to or better than those obtained with conventional tillage practices, protects soil against erosion, and results in increased storage of carbon in the soil. Researchers at Pacific Northwest National Laboratory are contributing to the no-till revolution by increasing understanding of the soil carbon sequestration process.

The buildup of CO2 in the atmosphere is a result of burning fossil fuels for energy production as well as the historical and current conversions of forests and grasslands to agricultural use.

Plants remove CO2 from the atmosphere through photosynthesis and release part of it back via respiration. This carbon cycling results in a net accumulation of plant biomass. When crops are harvested, the organic carbon in the plant residue and roots is decomposed by soil microbes, resulting in the release of CO2 back to the atmosphere. Not all the carbon is released, however. In aggrading natural ecosystems and well-managed agroecosystems, a portion of the added carbon is slowly converted into soil organic matter. Conversely, intensive tillage, erosion, inadequate nutrient management and the conversion of forests and grasslands to agriculture have led to carbon losses of up to 50 percent from that present in native ecosystems.

Carbon accumulation in agricultural soils can be greatly improved by various forms of conservation practices such as no-till agriculture, optimal nutrient management, crop rotations and converting marginal agricultural land back to native vegetation. Carbon sequestration occurs mainly when more carbon is added to the soil or when there is a decrease in soil disturbance.

"The central idea behind soil carbon sequestration is that most of the soil carbon lost worldwide due to past agricultural practices can be recovered during the next 30 to 40 years with the application of advanced agricultural technologies," said Cesar Izaurralde, senior scientist at PNNL's Joint Global Change Research Institute. "There is increasing experimental evidence to support this assertion. The challenge resides in providing incentives on a global scale for farmers to adopt no-till and other technologies. It also is necessary to develop monitoring systems to demonstrate that the accumulation of soil carbon occurs because of the adoption of these practices."

Researchers estimate that the extensive adoption of no-till agriculture, diversified rotations, cover crops, fertility management, erosion control and irrigation management can lead to the recovery of two thirds of the carbon that has been lost from the soil due to conversion of native ecosystems to agriculture and the use of conventional management practices. That amounts to 40 to 50 billion tons of carbon. As a reference, fossil fuel emissions of carbon to the atmosphere exceed six billion tons a year.

Izaurralde and colleagues at JGCRI and at PNNL's Richland, Wash., campus have developed models to better understand how carbon is sequestered in the soil. One program, supported by the U.S. Department of Energy, is Carbon Sequestration in Terrestrial Ecosystems, CSiTE; the other, supported by the U.S. Department of Agriculture, is the Consortium for Agricultural Soils Mitigation of Greenhouse Gases, CASMGS.



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