Second, the descending inflection points in the pH dynamics of
PBV and PBS lagged strongly behind the point in the dynamics of
PBA (Fig. 3). The timescale of the inflection points of PBV and PBS
was similar to that of ascending inflection points in previous studies (Yuan and Xu, 2011), which suggests that the first few
weeks after biochar addition to soils should be a dramatic and
valuable period for studying soil acidity amendment. Liable C
fractions in the fresh biochar in the soil are decomposing during
this period, whereas those in PBa have been lost largely after
around 4 months under ventilated environmental condition (see
volatile matter and DOC contents in Table 2), because biochar
weathering occurs within several weeks when applied to soils
(Kuzyakov et al., 2009). In fact, minor differences in liable C
fractions were found between biochar PB aged for 4 months and
those aged for 10 years (unpublished result). Therefore, the
ameliorating effect of biochar on soil acidity can be prolonged,
even if it initially declines, considering that most fractions in the
biochar are inert and can stably persist in soils.