Brodowski (2006) found a small proportion of biochar particles in soil to be associated with
micro-aggregates, but for this biochar to account for a rather large proportion of the carbon
that is present in such structures i.e. compared to other particulate organic matter. The
authors used this as evidence for physical protection of biochar against degradation and also
noted that biochar might act as a binding agent for organic matter in aggregate formation.
Although they did not specify whether the latter would be a purely physical interaction or a
consequence of biological activity, Watts (2005) previously found no effect of charcoal on
aggregation at low temperatures designed to preclude biological activity. In an earlier
publication Glaser (2000) found a large proportion of biochar in terra preta to be present in
unprotected fractions. Obtaining similar results, Murage (2007) noted that the misleading
impression might be gained that active soil fractions turn over more slowly in soils that are
enriched in biochar.