Jim Kling's Library tagged alternative-energy →  View Popular

The main stimulus for this interest was the work of Wim Sombroek, who died in 2003 and is still mourned in the field. Sombroek was born in the Netherlands in 1934 and lived through the Dutch famine of 1944 — the Hongerwinter. His family kept body and soul together with the help of a small plot of land made rich and dark by generations of laborious fertilization. Sombroek's father improved the land in part by strewing it with the ash and cinders from their home. When, in the 50s, Sombroek came across terra preta in the Amazon, it reminded him of that life-giving 'plaggen' soil, and he more or less fell in love. His 1966 book Amazon Soils began the scientific study of terra preta.

Since then trial after trial with crop after crop has shown how remarkably fertile the terra preta is. Bruno Glaser, of the University of Bayreuth, Germany, a sometime collaborator of Sombroek's, estimates that productivity of crops in terra preta is twice that of crops grown in nearby soils². But it is easier to measure the effect than explain it through detailed analysis.

Everyone agrees that the explanation lies in large part with the char (or biochar) that gives the soil its darkness. This char is made when organic matter smoulders in an oxygen-poor environment, rather than burns. The particles of char produced this way are somehow able to gather up nutrients and water that might otherwise be washed down below the reach of roots. They become homes for populations of microorganisms that turn the soil into that spongy, fragrant, dark material that gardeners everywhere love to plunge their hands into. The char is not the only good stuff in terra preta — additions such as excrement and bone probably play a role too — but it is the most important factor.