One calculation by Robert Brown, director of the Office of Biorenewables Programs at Iowa State University, revealed that if the U.S. adopted a cap and trade program in CO2 emissions like the one already in place in the European Union, farmers in the Midwest could almost double their income by using corn stover—the leaves, stalks and cobs that remain after harvest—to fuel pyrolysis.
The use of char also promises to combat marine dead zones, like that in the Gulf of Mexico caused by nitrogen- and phosphorus-rich agricultural runoff. Char reduces the need for man-made fertilizers by helping the soil retain nutrients. In addition, it can be made out of the very same manure and sewage that would otherwise pollute the oceans.
Agrichar is not a recent invention. Rather, it is a modern-day attempt to re-create the terra preta, or dark soils that cover some areas of the Brazilian Amazon. These soils were created over thousands of years by pre-Columbian Indians, who covered their fields with the charred remains of domestic and agricultural trash. This practice boosted the carbon content of the soils from a meager 0.5 percent to 9 percent.
"This is actually slash-and-char agriculture," Brown notes, contrasting it with the modern day slash-and-burn variety. "Instead of biomass being burnt down to a fine ash, charcoal remains, just like after a campfire." In addition to retaining nutrients, the porous charcoal helps microorganisms colonize and build up the soil. Charcoal is known for remaining stable over long periods of time, and alternating rainy and dry seasons preserve it even more. "You basically are drying out a steak," explains Danny Day, president of Eprida, a renewable energy development company based in Athens, Ga. "So you get beef jerky, which will last you for years." Even today, the Amazonian dark earths are so fertile that farmers continue to till them.
"What we're looking at is producing those kinds of charcoals in a modern pyrolysis reactor," notes Brown, who received a $1.8 million grant from the U.S. Department of Agriculture (USDA) to attempt to recreate terra preta using corn stalks. He plans to have enough char generated by this spring to run field trials this year. By his calculations each square mile of corn farm that uses this "fiber to fertilizer" pyrolysis process can offset the emissions of 330 automobiles.
But is it Viable?
As with all new technologies, many questions about the ultimate utility of agrichar have yet to be answered. "As of now agrichar is not a uniform product," explains John Kimble, a retired USDA soil scientist. "And there's no easy way for farmers to apply it with existing equipment. They also need to know there is a large enough source of the material. Farmers are driven by profit, as is everyone, and they need to be shown that it will improve their bottom line."
Complicating debates about the costs of agrichar is the paucity of data on the subject. "No one is sure what types of biomass should be used as raw material," Kimble notes, "or exactly what production methods work best, so calculating the costs is really an exercise in speculation."
In addition, scientists are finding it hard to replicate the original terra preta soils. "The secret of the terra preta is not only applying charcoal and chicken manure—there must be something else," says Bruno Glaser, a soil scientist at Bayreuth University in Germany. Field trials in Amazonia using charcoal with compost or chicken manure find that crop yields decline after the third or fourth harvest. "If you use terra preta you have sustaining yields more or less constantly year after year," he says.
"I'm skeptical about adding just a pure carbon source," says Stanley Buol, a professor emeritus from the Department of Soil Science at North Carolina State University's College of Agriculture and Life Sciences who spent 35 years studying Amazonian soils. "It will be black and look good," but will it contain enough inorganic ions, such as phosphorus and nitrogen, essential to plant growth?"