2.3. CO2 release from mineralization of organic carbon and inorganic
carbonates
In this experiment 24 treatments were set with three replicates,
consisting of 6 controls with soils only and 18 treatments with permutations
of 6 soils and 3 biochars. For the controls, 5 g soil was incubated
in 40 ml sample vials. For the treatments, 5 g soil and 100 mg biochar
were thoroughly mixed in 40 ml sample vials. These treatments were
heat-treated at 160 °C for 2 h. Deionized water of 80% water holding capacity
with excessive concentration of NaN3 or HgCl2 in a mass ratio of
0.5% was added to maintain the sterile state. For soils S1, S2, and S3
(pH b 7.0), HgCl2 was added to sterilize. For the other soils (pH N 7.0),
NaN3 was used to sterilize. The headspace CO2 was measured as cumulative
CO2 release by using the method described in Section 2.3.
The CO2 release from mineralization of organic carbon was calculated
by subtracting abiotic from the total CO2 emission. The effect of biochar
application on the total CO2 emission and CO2 release from
mineralization of organic carbon was calculated as: (CT − CS)/
CS × 100%, where CT is the total C mineralized from the biocharamended
soil, CS is the amount of CO2-C evolved from the control soil.
The effect was calculated as percentage (%) of non-biochar treatment.
Furthermore, CO2 release from inorganic carbon/total CO2 emission
(IC/TC) ratio was used to calculate the contribution of abiotic process
for soils.