If you want to do something about global warming, look under your feet. Managed well, soil's ability to trap carbon dioxide is potentially much greater than previously estimated, according to Stanford researchers who claim the resource could "significantly" offset increasing global emissions. They call for a reversal of federal cutbacks to related research programs to learn more about this valuable resource.

The work, published in two overlapping studies Oct. 5 in Annual Review of Ecology, Evolution and Systematics and Global Change Biology, emphasizes the need for more research into how soil - if managed well - could mitigate a rapidly changing climate.

"Dirt is not exciting to most people," said earth system science professor Rob Jackson, lead author of the Annual Review of Ecology, Evolution and Systematics article and coauthor of the Global Change Biology paper. "But it is a no-risk climate solution with big cobenefits. Fostering soil health protects food security and builds resilience to droughts, floods and urbanization."

Humble, yet mighty
Organic matter in soil, such as decomposing plant and animal residues, stores more carbon than do plants and the atmosphere combined. Unfortunately, the carbon in soil has been widely lost or degraded through land use changes and unsustainable forest and agricultural practices, fires, nitrogen deposition and other human activities. The greatest near-term threat comes from thawing permafrost in Earth's northern reaches, which could release massive amounts of carbon into the atmosphere.

Despite these risks, there is also great promise, according to Jackson and Jennifer Harden, a visiting scholar in Stanford's School of Earth, Energy and Environmental Sciences and lead author of the Global Change Biology paper.

Improving how the land is managed could increase soil's carbon storage enough to offset future carbon emissions from thawing permafrost, the researchers find. Among the possible approaches: reduced tillage, year-round livestock forage and compost application. Planting more perennial crops, instead of annuals, could store more carbon and to reduce erosion by allowing roots to reach deeper into the ground.

Jackson, Harden and their colleagues also found that about 70 percent of all sequestered carbon in the top meter of soil is in lands directly affected by agriculture, grazing or forest management - an amount that surprised the authors.

"I think if beer bets were involved, we all would have lost," Harden said of her coauthors.

Jackson and his coauthors found a number of other surprises in their analysis. For example, plant roots are ?ve times more likely than leaves to turn into soil organic matter for the same mass of material. The study also provides the most complete estimate yet of carbon in peatland and permafrost - almost half of the world's estimated soil carbon.

"Retaining and restoring soil organic matter helps farmers grow better crops, purifies our water and keeps the atmosphere cleaner," said Jackson, Michelle and Kevin Douglas Provostial Professor in the School of Earth, Energy and Environmental Sciences.

Overcoming obstacles
The Jackson-led study describes an unexpectedly large stock of potentially vulnerable carbon in the northern taiga, an ecosystem that is warming more rapidly than any other. These carbon stocks are comparatively poorly mapped and understood.

The study warns of another danger: overestimating how the organic matter in soil is distributed. Jackson and his coauthors calculate there may be 25-30 percent less than currently estimated due to constraints from bedrock, a factor previously not analyzed in published scientific research.

While scientists are now able to remotely map and monitor environmental changes on Earth's surface, they still don't have a strong understanding of the interactions among biological, chemical and physical processes regulating carbon in soils. This knowledge is critical to understanding and predicting how the carbon cycle will respond to changes in the ecosystem, increasing food production and safeguarding natural services we depend on, such as crop pollination and underground water storage.

A rapidly changing climate - and its effects on soil - make these scientific advances all the more urgent.

"Soil has changed under our feet," Harden said. "We can't use the soil maps made 80 years ago and expect to find the same answers."

However, funding pressures such as federal cuts to climate science, combined with turnover in science staff and a lack of systematic data threaten progress on soil carbon research. Jackson, Harden and their colleagues call for a renewed push to gather significantly more data on carbon in the soil and learn more about the role it plays in sequestering carbon. They envision an open, shared network for use by farmers, ranchers and other land managers as well as policymakers and organizations that need good data to inform land investments and conservation.

"If we lose momentum on carbon research, it will stifle our momentum for solving both climate and land sustainability problems," Harden said.

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