TOPICS:General research and char research aimed at returning carbon through processes | Biochar applications for carbon sequestration

TERRA PRETA: A POSSIBLE MODEL FOR CARBON SEQUESTRATION

	A sharp contrast in color and fertility between the original subsoil and the anthropic Terra Preta horizon. Notice the weeds growing on the strip where eroded Terra Preta was cached in a score.

Charcoal enriched soils (e.g. Terra Preta and Chernozem) are among the most productive soils in the world. The Terra Preta is anthropogenic and occurs in patches (of up to 300 ha in size) along the rivers in the Amazon basin. Besides the ceramics it is one of the only cultural remains of the pre-Columbian civilization. Evidence that Terra Preta was man-made, proving the feasibility to transform one of the most infertile soils into one of the most productive, inspired charcoal research.

Slash and char was described as an alternative practice to slash and burn and charcoal is currently used by some Amazonian settlers to improve soil fertility. If biomass is burned, only a very small percentage of the carbon is converted into charcoal, but when pyrolyzed, charcoal production can capture 50% of the carbon stored in biomass. Charcoal when used as a soil amendment (biochar) shows very high recalcitrance against biological or chemical decay and stores carbon over centuries or millennia.

Conservation and restoration of soil organic matter (SOM) is of crucial importance to maintain soil fertility. Biochar management holds out the prospect to rapidly increase SOM and maintain it in soils for long periods of time.

SEE ALSO:Biochar.org: Balance Carbon and Restore Soil Fertility

Left: Ceramic remains in Terra Preta. Center: Charcoal particles in Terra Preta. Right: Sharp contrasts between Terra Preta horizon and ordinary ferralsols (photos by Ilse Ackermann and William Woods)

Most potting soils, herbicides in carbon-based formulations, and culture media formulations contain charcoal or activated carbons, although the scientific rationale for these applications is not always known. Recent studies showed that biochar amendments are indeed capable of increasing soil fertility. Biochar can improve soil chemical, biological, and physical properties, but the mechanisms of fertility enhancement are not completely discerned. The effects on soil biology seem to be essential as charcoal has the potential to alter the microbial biomass and composition.

Left: Sharp contrasts between Terra Preta horizon and ordinary ferralsols. Center: Vegetable cash crop production on Terra Preta. Right: Turf cash crop production on Terra Preta

On a global scale, the total carbon release flux due to fire is almost as large as that from fossil fuel consumption. This emphasizes the potential for C management by only using biomass that would otherwise be ablaze each year. The global potential of biochar reaches far beyond slash and char. Inspired by the recreation of Terra Preta, most biochar research was restricted to the humid tropics. More information is needed on the agronomic potential of charcoal, the potential to use alternative biomass sources (crop residues) and production of byproducts to evaluate the opportunities for adopting a biochar system on a global scale. Biochar as soil amendment needs to be studied in different climate and soil types. Today, crop residue biomass represents a considerable problem as well as new challenges and opportunities.

Left: UGA researchers K.C. Das and Christoph Steiner at a typical charcoal production site in the Brazilian Amazon. Right: Char application to banana planting holes at the EMBRAPA research station in Brazil

A system converting biomass into energy (e.g. hydrogen-rich gas) and producing charcoal as a byproduct might offer an opportunity to address these problems. Charcoal can be produced by incomplete combustion from any biomass, and it is a byproduct of the pyrolysis technology used for biofuel and ammonia production. Energy from crop residues could lower fossil energy consumption and CO₂ emissions, and become a completely new income source for farmers and rural regions. The biochar byproduct of this process could serve to recycle nutrients, improve soils and sequester carbon.

UGA's Biochar Research and Outreach Group focuses on the following broad areas of work:

1. Biochar production technology that is combined with other co-products
2. Impact of production process methods on biochar properties
3. Identification of optimal properties of biochar
4. Bench-scale, greenhouse and field studies of biochar use with various crops
5. Nutrient and carbon cycling aspects of biochar use

Left: The UGA/EPRIDA biorefinery. Renewable energy production out of biomass coupled with charcoal carbon sequestration produces energy with carbon negative emissions (i.e. each unit of energy produced reduced CO2 from the atmosphere). Right: Measuring soil respiration after field application of biochar in Tifton, Georgia