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Carbon is the key

Research in the Amazon region suggests that ancient farmers dramatically improved poor soilsthrough the addition of charcoal-based carbon

By Paul Hepperly

Editors' note:

As New Farm Research and Training Manager at The Rodale Institute, Dr. Paul Hepperly hasbeen a regular contributor to NewFarm.org for some time, providing research updates, op-ed

pieces, and white papers on topics like carbon sequestration in organic farming systems.

Dr. Paul Hepperly

None of those venues do full justice to the range of Paul's experience, however. Paul grew up

on a family farm in Illinois and holds a Ph.D. in plant pathology, an M.S. in agronomy and aB.S. in psychology from the University of Illinois at Champaign-Urbana. He has worked for

the USDA Agricultural Research Service, in academia, and for a number of private seed

companies, including Asgrow, Pioneer, and DeKalb. He has overseen research in Hawaii,Iowa, Puerto Rico, and Chile, and investigated such diverse crops as soybeans, corn, sorghum,sunflowers, ginger, and papaya. He has witnessed the move toward biotech among the

traditional plant breeding community and the move toward organics among new wave of

upcoming young farmers. Beford coming to the Rodale Institute Paul worked with hill farmersin India to help them overcome problems with ginger root rot in collaboration with Winrock

International.

Now we've decided to give Paul his own column, in which he can report on agricultural

research from around the world and reflect on its relevance to The Rodale Institute's research

program and to the progress of sustainable agriculture more generally in light of his own broad

perspective. Enjoy.

April 20, 2005: The yellow and red soils of the Amazon Basin are infamous for their low

fertility and poor ability to provide the vital nutrients needed for optimal plant growth anddevelopment. In addition, they are notoriously leaky, rapidly shedding applied nutrients from

fertilizers and/or manures. If this wasnt bad enough, when they become acid these yellow and

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red soils make high amounts of aluminum and manganese available to plants, thus causing acute

plant toxicities resulting in poor crop production and crop failures.

Despite these seemingly insurmountable deficiencies, pre-Columbian indigenous farmers in the

Central Amazonian plains converted these infertile and incipiently toxic soils into fertile black

terrain covering an area the size of modern-day France. Today, these relict black soils have highlevels of organic matter and A horizons as deep as one to two metersin contrast to surrounding

yellow and red soils, with A horizons of just 10 to 20 centimeters. Amerindian black soils haveimportant implications for agricultures attempt to feed exploding world populations and formitigating the rise in atmospheric carbon dioxide levels.

Despite having been abandoned hundreds of years ago, these soils have retained their fertility

and crop productivity. And this productivity holds up under renewed cultivation. In fact, Petersen

and his collaborators (2001) have shown that the productivity of some of these black soils in the

West Amazon region has been sustained over 40 years of continuous cultivation even withoutfertilization. This ability to retain plant nutrients and release them slowly has researchers from

the US, Germany, Japan, Brazil and elsewhere scurrying to unearth the mechanism behind thisblack soil conversion. Their results clearly show that carbon is the key.

Testing of these tropical black soils suggests that their high carbon content comes from charcoal.

To test this theory, researchers artificially amended yellow and red soils with charcoal and foundthat plant productivity and nutrition were drastically improved. Lehman and co-workers (2003)

showed that cowpea shoot and root growth and development were doubled in a yellow soil to

which 20 percent charcoal had been added. In addition, phosphorus, potassium, calcium, zinc,and copper were doubled and toxic manganese levels halved.

These results fly in the face of prevailing agri-chemical theories which hold that simple nutrient

salts alone are the key to plant production and nutrition. Evidently, the carbon content of thesesoils plays an important role in their fertility. Practitioners of organic agriculture have long

argued that soil organic matter and carbon content is critical to plant health. These findings point

once again to the wisdom of nature and biology over industrial chemistry.

We look forward to seeing advances in natural technologies, such as composting, that willsupport real, long-term improvements in soil and plant productivity.

References

Lehmann, J., J Pereira da Silva, C. Steiner, T. Nehls, W. Zech and B. Glaser. 2003. "Nutrient

availability and leaching in an archaelogical Anthrosol and Ferralsol of the Central Amazonbasin: fertilizer, manure and charcoal amendments." Plant and Soil 249: 343-357.

Petersen, J. B., E. Neves, and M. Heckenberger. 2001. "Gift from the past: Terra Preta andprehistoric Ameriindian occupation in Amazonia."In Unknown Amazonia, C. McEwan, ed., pp.

86-105. London: British Museum.