During the incubation duration, the values of Bd kept higher in the
biochar-amended soils than in the control after 21 d. Before 21 d, the
rapid increase in the control's Bd might be caused by gradual infilling of
clays into pores of the soil,which reflected that the incubated soils are stable
and approached field condition after 21 d. For the biochar-amended
soils, physical dilution effects might have caused reduced Bd levels,
which agreed with Busscher et al. (2011) who indicated that increasing
total organic carbon by the addition of organic amendments in soils
could significantly decrease Bd. Furthermore, the decrease in Bd of the
biochar-amended soils appears to have also been the result of alteration
of soil aggregate sizes, as shown by Tejada and Gonzalez (2007) who
amended the following soils by using organic amendments in Spain. In
our study,micromorphological observations of the amended soils indicated
the flocculation of soil microaggregates after the addition of biochar
(Fig. 4a; b).