Other than chemical properties, the incorporation of biochar into
the soil has also been found to influence microbial activity. Previous
studies have used MBC as an indicator to evaluate microbial activityin soils (Chan et al., 2008; Kimetu and Lehmann, 2010). In this
study, the higher MBC contents were always found in the biocharamended
soils at 0 d, 63 d and 105 d, indicating that biochar application
could effectively increase microbial activity in the soils. In
addition, the highest microbial activity was considered to occur at
date of 21 d, even the control soil, because the highest MBC contents
were found at 21 d for each treated soil (Fig. 3). Furthermore, the result
showed that the significantly higher MBC content was still found
in the 5% biochar-amended soil at the end of the incubation (105 d).
This indicated that higher application rate of the biochar could maintain
microbial activity in the soils for a longer period. Liang et al. (2006) indicated
thatmicrobial populations could be even higher in soil rich in black
carbon. The higher MBC contents in the biochar-amended soils could be
attributed to a higher pH (5.0–6.0) in these soils than in the control. The
pH in the 5% biochar-amended soil was more suitable for the growth
of microbes, especially for fungal hyphae, which also agreed with
Wuddivira et al. (2009). That increased pH in the biochar-amended
soils lead to an increase in microbial activity was further demonstrated
by a significantly positive correlation between pH and MBC in the soils
(Table 3). Additionally, the biochar was characterized by porous structure
(Fig. 1a). Because of this porosity, higher amounts of biochar in
the treated soil increased the habitat for microbes to grow. Joseph et al.
(2010) indicated that most of biochar has a high concentration of
macro-pores that extends from the surface to the interior, and minerals
and small organic particles might accumulate in these pores.