Terra Pretas: Charcoal Amendments Influence on Relict Soils and Modern Agriculture

Most soils found in the Amazon region are characterized by highly weathered profiles that are incapable of long-term agricultural production. However, small patches of highly fertile relict soil referred to as Terra Pretas, are also found in the Amazon region, and have maintained their integrity for thousands of years. These soils were anthropologically formed, being of pre-Columbian origin and are unique in their high amounts of charcoal and nutrients compared to the surrounding soils. The charcoal serves to stabilize the organic matter in the soil, increase cation exchange capacity, and increase water retention due to its porous structure and high surface area. Organic wastes, such as bones and manure are thought to be the source of additional nutrients. To improve the overall productive capacity of the soil in this region, slash and char has been proposed to replace the traditional practice of slash and burn to mimic the high amounts of charcoal found in Terra Pretas soils. Instead of burning the vegetation and releasing the carbon into the atmosphere, the vegetation would be charred and the carbon would be sequestered in the soil on a small scale. Furthermore, based on the stability of charcoal and its ability to sequester carbon, some scientists are suggesting we consider pyrolysis (the process that creates charcoal by heating organic material with low amounts of oxygen) and its byproducts as a solution to soil quality issues, global warming, and peak oil. This concept is very controversial and relatively unstudied; further research is needed to truly understand the feasibility and consequences of sequestering large amounts carbon in the soil and the use of biofuels formed as byproducts of pyrolysis.