significantly reduced electrical conductivity during the first 2 weeks,
whereas the nitrogen, compost and rockstone treated A2 biochar caused
13–160% increase compared to the untreated control. After 7 weeks the
0.1% A1 biochar amended soil showed a 24% increase in EC compared to
the control. However the higher application doses of A1 did not show
significant changes at the end of the experiment. Both the 0.5% A1 and
B1 application combined with compost or fertilizers increased the electrical
conductivity after 7 weeks.
3.2. Effects of treatments on soil microorganisms
The results of aerobic heterotrophic bacterial and fungal cell concentrations
show highly different responses to the biochar amendments.
On the other hand the results clearly demonstrate that biochar treatment
did not have negative effects on soil microbes since they can
grow in the biochar treated soils. In addition, at the end of the incubation
period, amendment with 0.5% and 1% A1 biochar (without other
additives) resulted in a slight increase (appr. 25%) of the aerobic heterotrophic
cell concentrations compared to the control (Fig. 3).
The addition of compost or NPK significantly enhanced bacterial
activity (e.g. 130% increase with 0.5% A1+ compost). The increase of
the bacterial cell concentration upon A1 biochar application could be
explained by the elevation of the low soil pH and by the available phosphorous
amount input as a result of the amendment. However, in the
case of B1 and A2 biochar we couldn't observe any significant effect
on the bacterial cell concentration after 2 and 7 weeks incubation time.
Although in most cases the biochar addition did not increase considerably
the bacterial cell concentration in soil but it did not decline either,
so the living conditions were appropriate for soil bacteria.
The values of fungal cell concentrations do not show a clear and
definite response to biochar addition (Fig. 4). The most remarkable influence
was exhibited by the A1 biochar amendment compared to the
control: the sudden increase (30–80%) at the start was followed by a
slight decrease after 2weeks,while at the end the fungal cell concentration
slightly increased (at 1% A1 rate) in comparison with the control.
The bacteria:fungi ratiowas calculated on the basis of cell concentrations
in the soil (data not shown). A shift to a higher bacteria:fungi ratio
was observed in biochar amended soils in line with expectation.
Bacteria:fungi ratio was 1.5–2.5 in soils without biochar amendment,
while in A1 treated soils this ratio ranged between 3.5 and 7.