The argument for encouraging biochar use as a ubiquitous household practice is compelling: Improved garden soil will increase food production where it has the most impact on energy demand. Implementing charcoal manufacture at a household level draws in a supply of yard prunings and workbench scraps that otherwise would be lost to non-charcoal alternatives. Unfortunately, finding even the most basic information on how to implement biochar use as a personal sustainability practice is discouragingly time consuming. In response I have started up a FAQ

Charcoal cannot replace the need for adding mineral nutrients.

Application of the charcoal to soils may be key to sustainability. Application of charcoal to soils is hypothesized to increase bioavailable water, build soil organic matter, enhance nutrient cycling, lower bulk density, act as a liming agent, and reduce leaching of pesticides and nutrients to surface and ground water. The half-life of C in soil charcoal is in excess of 1000 yr. Hence, soil-applied charcoal will make both a lasting contribution to soil quality and C in the charcoal will be removed from the atmosphere and sequestered for millennia.

The Godfather of Terra Preta, soil scientist Wim Sombroek (1934 - 2003) enjoyed a lifelong fascination with enhanced soil. The importance of plaggen soil in his native Netherlands impressed him at an early age, and early in the 1960's, he recognized in the Amazonian Dark Earths something familiar and precious. Before his passing, he assembled specific soil scientists challenged them to discover the process for making and sustaining a modern equivalent of the bio-char enhanced terra preta, what he termed terra preta nova. A great opportunity in answering Sombroek's challenge lies is surmounting the opacity of mutualistic rhizospheric species to traditional analytical approaches: only 1% of rhizospheric species are cultureable ala petri dish. We don't have a robust body of culture-independent studies against which to compare Terra Preta, so we are doubly challenged to reverse-engineer the phenomenon. Considering Wim Somboek's many noteworthy accomplishments, the perspective of his international leadership, and the late-in-life timing of his challenge, one senses he is pointing us to a mystery fundamental to understanding soil in new and exciting ways. This happens at a time when the soil science profession is in dynamic transition and sorely in need of a unifying vision. Wim Sombroek has given soil scientists a most welcome and worthy quest.

Peak Energy has a long post on Terra Preta that brings together what has been established on the subject. As of yet, there is no direct mention of the role of glomalin , just a minor mention of the mutualistic fungi that produce it. Glomalin is an unvalidated factor in Terra Preta formation that several of us sense will be demonstrated by soil research as fundamentally important. Spurred on by back40, I am fascinated with bio-char, Terra Preta's key soil amendment. Last summer I constructed a small charcoal retort out of a cracker tin. I used it to produce small pilot batches of low temperature charcoal. Hoping to transform my simple charcoal into a reasonably bio-char-like material, I am currently composting my bits.

Rapid turnover of organic matter leads to a low efficiency of organic fertilizers applied to increase and sequester C in soils of the humid tropics. Charcoal was reported to be responsible for high soil organic matter contents and soil fertility of anthropogenic soils (Terra Preta) found in central Amazonia. Therefore, we reviewed the available information about the physical and chemical properties of charcoal as affected by different combustion procedures, and the effects of its application in agricultural fields on nutrient retention and crop production. Higher nutrient retention and nutrient availability were found after charcoal additions to soil, related to higher exchange capacity, surface area and direct nutrient additions. Higher charring temperatures generally improved exchange properties and surface area of the charcoal. Additionally, charcoal is relatively recalcitrant and can therefore be used as a long-term sink for atmospheric CO2. Several aspects of a charcoal management system remain unclear, such as the role of microorganisms in oxidizing charcoal surfaces and releasing nutrients and the possibilities to improve charcoal properties during production under field conditions. Several research needs were identified, such as field testing of charcoal production in tropical agroecosystems, the investigation of surface properties of the carbonized materials in the soil environment, and the evaluation of the agronomic and economic effectiveness of soil management with charcoal.

The article highlights some important nuances. Terra mulata, the lighter type of terra preta, covers much more area than the celebrated black type central to the concept of terra preta.

Why people living on hills overlooking many rivers in Brazil two millennia ago devised this approach is still a subject of debate, as is how they added all the extra organic content and ensured the soil was teeming with beneficial bugs and other micro-organisms. A modern technology called low-temperature pyrolysis can produce bio-char on an industrial scale. Using wood or agricultural wastes for fuel, pyrolysis would generate heat for electricity while also actually reducing net emissions of carbon dioxide since the organic matter would otherwise decompose. "This might be the beginning of a bio-char revolution," Lehmann says.

Applying the knowledge of terra preta to contemporary soil management can decrease the amount of fertilizer needed, because bio-char helps retain nitrogen in the soil as well as higher levels of plant-available phosphorus, calcium, sulfur and organic matter. The black soil also does not get depleted, as do other soils, after repeated use. Producing and applying bio-char to soil would not only dramatically improve soil and increase crop production, but also could provide a novel approach to establishing a significant, long-term sink for atmospheric carbon dioxide.