LAFAYETTE, Ind. — Supported by science and spurred by emerging markets, more than 80 participants in an international workshop on carbon sequestration called on world policymakers to focus research and create fair-priced carbon offset markets that would pay farmers to adopt conservation agriculture practices that will capture carbon in the soil.
Carbon offset markets would allow farmers to sell the service of capturing and storing, sequestering, carbon from the atmosphere. In turn, that would help offset the levels of greenhouse gases emitted by human activity, essentially locking up enough carbon in the soil to cancel out airborne emissions of tons of carbon dioxide, methane and nitrogen oxide.
Currently, carbon credits from industrial sources are widely traded, but soil carbon has generally not been a marketable commodity.
The meeting, called the Conservation Agriculture Carbon Offset Consultation, was hosted by the Conservation Technology Information Center and the Food and Agriculture Organization of the United Nations at the Purdue University campus Oct. 28-30.
“To create working markets for farmers’ efforts to capture atmospheric carbon, we need to understand the science of how carbon acts in the soil, and the science behind no-till systems,” said Karen Scanlon, executive director of Conservation Technology Information Center.
“With that insight, we can quantify the effect that farmers have with specific practices and on specific soils, and create a fair compensation structure for those effects.”
After sharing their research results and field experiences from six continents, the participants spent several hours at the end of the meeting’s third day in a discussion, hammering out a position statement calling for the inclusion of soil carbon in worldwide carbon offset markets.
“This has been one of the better meetings I’ve been to because the focus has been on ‘this is what we know, these are the answers we have, this is what we can accomplish today,’ rather than focusing on the problems we have and what we don’t know,” said Dan Uthe, an industrial process consultant with Novecta in Johnson, Iowa.
The first day of the consultation was dedicated to exploring the science of soil carbon sequestration in the soil. Researchers from the South American tropics, the Australian bush, Midwestern U.S. and China presented the results of their studies on how soil carbon levels responded to various tillage regimes.
Not surprisingly, there were no simple answers. Changes in soil carbon are small — imagine finding 1,000 pounds of carbon in a mass of soil 2.5 acres in area and 3-feet deep.
Complex chemistry dictates that the soil can only sequester a limited amount of carbon per year, and that after a certain number of years — scientists believe it is 15 to 20 years — a field reaches a plateau. To make it even more complex, the soil’s capacity to store carbon depends on soil type, tillage system, the use of cover crops, cropping history and how much carbon it lost in the first place.
Research from highly degraded soils in South America put into improved pasture showed dramatic jumps in carbon levels after five years — much higher storage than Midwestern soils in the U.S.
Deep-rooted pasture plants also have the capacity to place carbon deeper into poor South American soils than annual crops do in cooler climates with richer ground. However, Corn Belt farms have the capacity to capture and store significant amounts of carbon, too.
“The higher the clay content, the more capacity there is to store carbon,” said Charles Rice of Kansas State University.
Which practices help? The less tillage used, the better the sequestration of the carbon, according to many scientists at the meeting.
Though there were discussions on definitions of terms such as “conservation agriculture” and “no-till,” the data showed tillage burns soil carbon and releases greenhouse gases. The difference in the amount of crop residue required to rebuild soil carbon stocks also varied widely.
Joao Carlos de Moraes Sa of the University of Ponta Grossa in Brazil pointed out that tropical Brazilian soils consume 9 to 14 tons of crop residue per hectare each year — often in a matter of months — while Rice’s studies in Kansas showed three tons of residue per hectare in his state was enough to yield an increase in soil carbon.
In Brazil, Telmo Amado of the Federal University of Santa Maria plants corn and a deep-rooted, perennial pasture grass called Brachiata together for great sequestration results.
Tightly planted corn quickly grows tall, while shaded Brachiata sends roots deep into the soil. The result is a tremendous amount of biomass above and below the ground — a cash crop, a grazing opportunity and plenty of residue for carbon-fixing microbes.
But just growing biomass isn’t enough, says Amado. “One side of the equation is introducing this carbon,” he noted. “The other side is how we stabilize it in the soil. Both physical and chemical protections are important.”
That means protecting the soil surface with plenty of residue, maintaining soil structure by no-tilling or minimizing tillage, keeping soil microbes healthy (again through minimal soil disturbance), fertilizing crops adequately, avoiding soil compaction and rotating crops.
Further information on the consultation, no-till farming and carbon sequestration is available at http://www.conservationinformation.org .
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