A Perspective on Terra Preta and Biochar

Examining the controversy about terra preta reproducing itself, and what this may mean for the theory that terra preta is ancient biochar soil

The Modern Discovery of Terra Preta, and a Brief Modern History of Biochar

Is Terra Preta Charcoal Amended Soil?

Negative Priming

Electron Transfer Hypothesis

  • the geobattery mechanism, dominant in biochar produced at temperatures under 600˚C, which charges and discharges electron exchange chemical groups on its surface to exchange electrons with microbes that come in contact with these groups, and
  • the geoconductor mechanism, a much faster and much more prolific electron transfer mechanism, found in biochar produced at temperatures over 700˚C, which directly conducts electrons between microbes in contact with the char. A macroscopic piece of biochar visible to the naked eye can host millions of bacteria and archaea on its surface, along with contact to fungal hyphae. By directly conducting electrons among them, it serves as a microbial marketplace where electrons are the currency of exchange, removing the electron transfer bottleneck for all of their relevant biochemistry.

Biochar and the Natural Selection of the Terra Preta Microbiome

Co-composted Biochar

  • Biochars that were produced at lower temperatures, which are sometimes not fully devolatilized, start out hydrophobic, due to the presence of tar — condensed from the smoke released by pyrolysis. Until the tar is broken down (primarily by fungi that can digest tar) and the char is colonized by beneficial microbes, the tars have a preservative-like biocidal effect.
  • Biochars that are fully devolatilized, and especially biochars that have been exposed to reduction reactions (which we will look at in detail in later installments) have significantly higher adsorptivity, and behave like carbon filters in the soil, aggressively adsorbing and binding to nutrients, rather than loosely binding the nutrients like nutrient exchange sites in mature soil organic matter.

Speculations on the Origins of Terra Preta

Concluding Thoughts

Coming up next: The right way and the wrong way to do biomass energy



Climate drawdown and carbon sequestration in your back yard

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