Biochar is a type of charcoal produced from biomass. In some cases, the term is used to distinguish biomass charcoal produced via low-temperature burn process. Charcoal is the blackish residue consisting of impure carbon obtained by removing water and other volatile constituents from animal and vegetation substances. ...

Biochar is employed most commonly as a soil amendment. It has several qualities that make it suitable to this task:

• It is largely inert. Microbial composting action leaves charcoal largely unaffected.
• Highly porous. Serves both to retain water in the soil, and provide large surface area for microbes.

There is some empirical evidence that low-temperature biochar produces more robust growth in plants when compared to high-temperature biochar. It is speculated that it retains organic matter that is desirable to beneficial microbes (like mycorrhizal fungi), resulting in higher nutrient availability to the plants. Millions of years ago, trees, flowers and grasses faced many natural stresses, such as low soil fertility, drought and temperature extremes. ...

Biochar is the main (and likely key) ingredient in the formation of terra preta, or Amazonian dark earth. Terra preta (which means dark soil in Portuguese), refers to expanses of very dark soils found in the Amazon Basin. ...