Biochar from pyrolysis and conventional charcoal and char share key characteristics which
are related to carbon sequestration (long residence time) and soil fertility (soil conditioning
effect). This is important since there is currently a much greater amount of research for char
(Glaser et al., 2002) than for biochar. Biochar produced in association with bioenergy
generation may be more applicable in some countries than others, depending on economic
circumstance, political priorities, technology and infrastructure.
The central quality of biochar and char that makes it attractive as a soil amendment is its
highly porous structure, potentially responsible for improved water retention and increased
soil surface area. Addition of biochar to soil has also been associated with increased nutrient
use efficiency, either through nutrients contained in biochar or through physico-chemical
processes that allow better utilisation of soil-inherent or fertiliser-derived nutrients.
Importantly, it is the apparent biological and chemical stability that allows biochar to both act
as a carbon sink, as well as provide benefits to soil that are long-lived.
Using pyrolysis to turn sustainably produced biomass into a recalcitrant substance that is
decomposed at a much slower rate, constitutes both a tool for carbon sequestration and
avoided emission. It is argued that sequestration of carbon in biochar allows for a much
longer storage time compared with other terrestrial sequestration strategies, such as
afforestation (Schulze et al., 2000). The stability and carbon sequestration potential of
biochar in soil is examined in Section 3.1.2.